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# Galen, On Demonstration

Matyáš Havrda, Pauline Koetschet

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Matyáš Havrda, Pauline Koetschet

**Galen, On Demonstration**
Scientia Graeco-Arabica

Herausgegeben von
Marwan Rashed

Band 43
Matyáš Havrda, Pauline Koetschet

# Galen, On Demonstration

Reconstruction of a lost treatise
from Greek and Arabic sources

With English translations by
Pauline Koetschet, Matyáš Havrda, and Sean Coughlin

DE GRUYTER
The research for this book was funded by the Czech Science Foundation, project no. 20-16937S, implemented at the Institute of Philosophy of the Czech Academy of Sciences, and by Agence nationale de la recherche, project no. 18-CE91-0004.

ISBN 978-3-11-914989-1

e-ISBN (PDF) 978-3-11-157100-3

ISSN 1868-7172

DOI https://doi.org/10.1515/9783111571003

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## Foreword

Galen's *On demonstration (Dem.)* comprised fifteen books. Had it survived, it would have filled two massive volumes of the Teubner Library, some eight-to-nine hundred pages in total. But it has not survived (as far as we know) and what we have instead is a tiny fraction. Direct quotations from the treatise, whether preserved in Greek or in Arabic, cover approximately one percent of the original bulk; and if we include material whose attribution to *Dem.* is conjectural, we will not get beyond five percent even on the most optimistic scenario. Yet our information about its contents is much more complete and nuanced than it was in 1895 when Iwan von Müller made the last attempt to put all the testimonia together. We now have more than twice as much material as he did, thanks mainly to research in Arabic sources, which has yielded more than fifty testimonia unknown to von Müller. Moreover, the conjectural but widely accepted link between *Dem.* and (at least parts of) the so-called eighth *Stromateus* by Clement of Alexandria gives us an unprecedented insight into its style and structure. A few other Greek fragments have been brought to light, notably a reference (and possibly more) in a text from the Alexandrian Neoplatonist school called *All the kinds of syllogism*. Of course, our knowledge of *Dem.* is still fragmentary and the gaps are looming large. But it is time to revisit von Müller's pioneering attempt and give a fresh overview and interpretation of the evidence available to us. We believe and hope that more material will emerge in due course, especially in the Arabic manuscripts, and our grasp of this mysterious text will continue to be refined.

In this book we present the fruit of our collaboration, which began in 2019 and brought together two lines of research that we had been pursuing for the previous decade or so. Our collaboration combined two distinct but interdependent perspectives that were both vital to the task we set out to do: the perspective of an expert on late ancient and medieval Arabic philosophy focused on the reception of Galen in the Arabic-speaking milieu; and that of a historian of Greek philosophy, whose primary focus was Galen and his methodology of science. The book consists of two parts: the introduction (Part 1), and the collection of the testimonia, accompanied by notes and a translation into English (Part 2). The introduction falls into five chapters. In the first, we briefly discuss the Greek and Arabic sources of *Dem.* in the chronological order; in the second, we review the history of modern scholarship; in the third, we consider the title, datation, purpose, and intended audience of *Dem.*, as well as its genre; in the fourth, we reconstruct its structure and contents; and finally, in the fifth, we look at the Arabic testimonia – their sources, language, and doctrinal content – against the backdrop of Arabic philosophy. The collection of the testimonia is divided into seven sections, designated as A–G. The first section contains general and unlocated testimonia, i.e. those that refer to *Dem.* in general terms or cannot be plausibly located in a specific book. The arrangement of the following sections reflects the presumed sequence of topics in *Dem.* They contain the Arabic, Greek, and (in two cases) Latin material with textual comments, notes, and translation.

<figure><img src="image_4.png" /></figure>

<footnote>Open Access. © 2025 Matyáš Havrda, Pauline Koetschet, published by De Gruyter.</footnote>

<footnote>This work is licensed</footnote>
The book is a joint work, but the responsibility for its individual parts is divided as
follows. Pauline Koetschet has written chapter 5 and co-written chapter 1 of the intro-
duction, and produced the edition of the Arabic material, mostly based on the first-hand
study of manuscripts. Matyáš Havrda has written chapters 2–4 and co-written chapter
1 of the introduction and produced the edition of the Greek and Latin material, mostly
based on modern editions. English translations are pieced together from a variety of
sources, but most of them are the result of a collaboration that, apart from the editors,
included Sean Coughlin. For details about the edition and translations see introduction
to Part 2.

We are indebted to our respective home institutions – Matyáš Havrda to the Insti-
tute of Philosophy of the Czech Academy of Sciences and Pauline Koetschet to the
National Center for Scientific Research (CNRS) and the French Institute for the Near-
East (Ifpo) – for providing facilities for our work. Preliminary results of our research
were presented at seminars organized by the Institut für Orientalistik of the University
of Vienna and the Institute of Philosophy of the Czech Academy of Sciences, as well as
at the 11th colloquium of the International Society for the History of Arabic and Islamic
Science and Philosophy (SIHSPAI). We are grateful to the participants of these events
for their useful comments, especially István Bodnár, Riccardo Chiaradonna, Klaus Cor-
cilius, Christian Gastgeber, Orna Harari, Marwan Rashed, and Elvira Wakelnig. Other
colleagues who have given us advice on various aspects of our work over the years
include Jonathan Barnes, Philip van der Eijk, Kosta Gligorijevic, Jim Hankinson, Ben
Morison, and Christina Savino. We are particularly grateful to Riccardo Chiaradonna,
who read the first part carefully and gave us valuable comments, and Marwan Rashed,
who accepted the book in his series and contributed advice on the Arabic testimonia.
He is also the editor of the *Doubts about Galen* and the *Solution to the Doubts about
Galen*, and thereby engaged closely with these texts. Iktimal Rajab, who is the co-editor
of Abū al-‘Alā’ ibn Zuhr’s *Solution to the Doubts about Galen* with Pauline Koetschet,
read through all the Arabic testimonia. Robert Bostock revised our English in the first
part of the book. Pavel Nývlt provided us with editorial assistance and compiled the
index of citations. Finally, our thanks are due to De Gruyter’s Torben Behm and Florian
Ruppenstein for the exceptionally fast and thoughtful preparation of the manuscript
for printing. The book has been produced with the generous support of our national
research funders, Czech Science Foundation<fnref n="1" /> and Agence nationale de la recherche<fnref n="2" />.

<footnote n="1">1 Project GA 20-16937S.</footnote>

<footnote n="2">2 Project ANR-18-CE91-0004.</footnote>
# Contents

Foreword — V

Abbreviations — IX

## Part I Introduction

1 The sources of *On demonstration* — 3

2 Modern scholarship — 16

3 Title, date, purpose, audience, and genre — 24

4 Galen's *On demonstration*: Reconstruction of the contents — 34

5 The Arabic *On demonstration*: Transmission, translation, and interpretation — 71

## Part II The testimonia

Introduction to the edition of the testimonia — 91

Text / Translation — 95

Section A: General and Unlocated Testimonia — 96/97

Section B: Books I–III and Related Testimonia — 122/123

Section C: Book IV — 144/145

Section D: Book V — 160/161

Section E: Books VIII–IXa and Related Testimonia — 168/169

Section F: Books IXb, XI–XII, and Related Testimonia — 184/185

Section G: Books XIII–XIV — 194/195

Bibliography — 219

Sources of the Testimonia — 229

Index locorum — 233
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Abbreviations

ad loc. ad locum

add. addidit

Aët. Aëtius, *Placita philosophorum*

Ar. Arabic

Alex. Aphr. Alexander of Aphrodisias

Arist. Aristotle

C Coughlin

CAG Commentaria in Aristotelem Graeca

CCTC Cambridge Classical Texts and Commentaries

CGT Cambridge Galen Translations

Clem. Alex. Clement of Alexandria

CMG Corpus medicorum Graecorum

corr. correctum

del. delevit

DL Diogenes Laertius, *Lives of Eminent Philosophers*

fol. folio

Gal. Galen

H Havrda

K Kühn (1821–1833)

Ko Koetschet

lac. ind. lacunam indicavit

LCL Loeb Classical Library

lect. ... def. lectionem...defendit

LS A. A. Long & D. N. Sedley, *The Hellenistic Philosophers I–II* (Cambridge: Cambridge University Press 1987).

LSJ H. G. Liddell, R. Scott & H. S. Jones (eds.), *A Greek-English Lexicon: ninth edition, with a revised supplement* (Oxford: Oxford University Press 1996).

ms. manuscript, *liber manu scriptus*

mss. manuscripts

om. omisit

PhA Philosophia Antiqua

Philo Alex. Philo of Alexandria

Plat. Plato

prooem. prooemium

s.v. sub voce

SAM Studies in Ancient Medicine

sec. *secuta, secuti, secutus*

secl. *seclusit, secluserunt*

Simpl. Simplicius

SM Galeni Scripta minora

suppl. *supplevit*

SVF Hans F. A. von Arnim (ed.), *Stoicorum veterum fragmenta* (Leipzig: Teubner 1903–1924)

W Wakelnig

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Part I **Introduction**
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# 1 The sources of On demonstration

*On demonstration* (hereafter abbreviated as *Dem.*) is reconstructed from a multiplicity of sources, Greek and Arabic, starting from Galen and his near contemporaries and ending with Ibn Rušd and Maimonides in the 12th century. Many of these testimonies are mediated by other sources, now lost, most notably perhaps some works by Alexander of Aphrodisias. Of authors quoting from *Dem.* who apparently had access to the original text, or some of its parts, the latest are dated to the 6th century (the Alexandrian Neoplatonists), although we know that more than half of the treatise was still available in the 9th century, when it was translated into Syriac and Arabic. The last author who seems to quote directly from the Arabic translation is Abū al-‘Alā’ ibn Zuhr in the 12th century. In what follows, we offer a brief chronological overview and evaluation of all the sources we draw on in our reconstruction.

## Galen

Galen refers to *On demonstration* about forty times in twenty different works. This alone indicates how much importance he attached to the treatise. In his late bibliographic essays, and throughout his *oeuvre*, he explains why. He regards *Dem.* as a starting point for the study of his medical works, as well as the medical doctrines of other schools (A4, see also A6–7).<fnref n="3" /> He describes it as a compendium and training tool of “logical”, “rational” or “demonstrative” methods intended for students of medicine.<fnref n="4" /> His references to *Dem.* naturally occur for the most part in methodological sections of his works, for instance in the first book of *The therapeutic method (MM)* or the second book of *The doctrines of Hippocrates and Plato (PHP)*. The tenets invoked involve the method for dealing with a particular issue set up for inquiry, variously called τὸ ζητούμενον, τὸ προκείμενον πρᾶγμα/σκέμμα, τὸ προβεβλήμενον, τὸ πρόβλημα, etc. They include instructions about the order of inquiry, in which the starting point is the notion of the thing being sought – a notion agreed on by everyone – followed by the definition of the substance of the thing in question (A16–A19). They also include instructions about demonstrations and their premisses, namely, the requirement for these premisses to be scientific and appropriate (A20–A26); and about the first principles, which are things evident to the intellect or sense-perception (A12–A16). They also include remarks about induction (A27–A28).

<figure><img src="image_9.png" /></figure>

<footnote n="3">3 Throughout the book, we refer to the testimonia of *Dem.* under the section letter (A-G) and the testimonium's number within that section in the present collection. For instance, A4 is testimonium 4 in section A.</footnote>

<footnote n="4">4 See A4, A7, A13, A16, A18, and A28. We will discuss the intended audience and the purpose of the treatise in more detail below (Chapter 3).</footnote>
Apart from this methodological content, referred to in brief and general terms, Galen also mentions specific issues discussed in *Dem.*: embryology (B3); generation and corruption (C1); objects of vision (D1–D3); causes of vision (G10, G25–G27); the elements (G1, G2); and syllogisms (F2, F5). These references, too, are brief and, taken by themselves, provide meagre and inconclusive evidence about the actual contents of the treatise.

## Clement of Alexandria (2<sup>nd</sup>–3<sup>rd</sup> centuries)

This early Christian writer, one of the founding fathers of “Christian philosophy”, was Galen’s younger contemporary, active in Alexandria towards the end of the 2<sup>nd</sup> century (the first book of his *Stromateis* was written after 192 and he probably died before 221). He never mentions Galen by name, but an argument has been made that he used *Dem.* (or its parts, or an abridged version of it) as a source for the composition of philosophical notes preserved, along with other material, under the title “The eighth *Stromateus*”.<sup>5</sup> For the sake of convenience, we refer to these notes, covering pages 346<sup>v</sup>–361<sup>r</sup> of the Florentine manuscript Plut. 5.3, as *Liber logicus*.<sup>6</sup> After a brief (Christian) introduction (α), they include discussions about demonstration (β), the method of discovery (γ), two sections about ἐποχή (δ, ζ), and chapters on division and definition (ε), the categories (η), and causes (θ).<sup>7</sup> Although it has been argued that the whole of *Liber logicus* could be based on *Dem.*, the argument is more compelling (and more commonly accepted) in relation to sections β and γ than to the rest of the material.<sup>8</sup> We have found the internal and external evidence for these two sections strong enough to warrant including them among the testimonia of *Dem.* To distinguish them from direct testimonia, however, we mark them with an asterisk.<sup>9</sup> Additional evidence from Nemesius allows us to locate the source of these testimonia within the first three books of *Dem.*<sup>10</sup>

<footnote n="5">5 See M. Havrda, “Galenus Christianus? The Doctrine of Demonstration in *Stromata* VIII and the Question of Its Source,” *Vigiliae Christianae* 65 (2011), pp. 343–375; idem, *The So-Called Eighth Stromateus by Clement of Alexandria: Early Christian Reception of Greek Scientific Methodology* (Leiden: Brill 2016), pp. 34–50.</footnote>

<footnote n="6">6 For the text, see Havrda, *The So-Called Eighth Stromateus*, pp. 86–127.</footnote>

<footnote n="7">7 See Havrda, *The So-Called Eighth Stromateus*, pp. 27–28.</footnote>

<footnote n="8">8 This corresponds to *Lib. log.* (= *Strom.* VIII) 2.3.1–5.15.1 (81,9–88,33 Stählin–Havrda). See further below, pp. 17–18.</footnote>

<footnote n="9">9 See below, B6* and B7*. For the Galenic parallels, see the comments on the Greek text.</footnote>

<footnote n="10">10 For sections β and γ of *Lib. log.* (= B6* and B7* of the present collection) as drawing on one (or more) of the first three books of *Dem.*, see below, pp. 35–37.</footnote>
Alexander of Aphrodisias (2<sup>nd</sup>–3<sup>rd</sup> centuries)

Alexander, too, was Galen's younger contemporary, with a *floruit* of ca. 200.<fnref n="11" /> He refers to Galen by name (*In Top*. VIII.5, 549,24 Wallies) and Galen is probably his polemical target in the last part of his *De anima*, which discusses the location of the ruling part of the soul (*De an*. 94–100 Bruns–Sharples).<fnref n="12" /> In his (lost) commentary on Aristotle's *Physics*, Alexander countered Galen's criticism of Aristotle's argument in *Phys*. VII.1 on the prime mover.<fnref n="13" /> A more detailed version of Alexander's polemic against Galen about the unmoved mover (whether from the *Physics* commentary or from an independent treatise, as the Arabic tradition suggests) is preserved in an Arabic translation.<fnref n="14" /> Further, there is a report by Ibn al-Nadīm (10th century) that Alexander wrote a treatise against Galen on time and place, issues dealt with in Aristotle's *Physics* IV.<fnref n="15" /> Some scholars believe that a part of this treatise is identical with Alexander's *On time*, a short polemical text edited by A. Badawī (which, however, never mentions Galen by name).<fnref n="16" />

<footnote n="11">11 See D. Frede, "Alexander of Aphrodisias," in E. N. Zalta (ed.), *The Stanford Encyclopedia of Philosophy* (*Winter 2017 Edition*), <https://plato.stanford.edu/archives/win2017/entries/alexander-aphrodisias/>.</footnote>

<footnote n="12">12 T. Tieleman, “The Hunt for Galen’s Shadow: Alexander of Aphrodisias, *De An*. pp. 94.7–100.17 Bruns Reconsidered,” in K. Algra, D. T. Runia, and P. W. van der Horst (eds.), *Polyhistor: studies in the history and historiography of Greek philosophy presented to Jaap Mansfeld on his 60th birthday*, (Leiden: Brill 1996), pp. 265–283. For Alexander’s reception of Galen see the bibiliography in P. N. Singer, “Galen and the philosophers: philosophical engagement, shadowy contemporaries, Aristotelian transformations,” in P. Adamson, R. Hansberger, and J. Wilberding (eds.), *Philosophical Themes in Galen* (London: Institute of Classical Studies 2014), pp. 7–38, here pp. 21–22 n. 43.</footnote>

<footnote n="13">13 This is reported by Simplicius, *In Phys*. VII.1 (1039,13–1040,12 Diels); and confirmed by a Byzantine scho-
lion on Aristotle’s *Physics*, published by Marwan Rashed: see M. Rashed, *Alexandre d’Aphrodise, Commen-
taire perdu à la Physique d’Aristote (Livres IV–VIII: Les scholies byzantines*, de Gruyter 2011, p. 424, schol. 432.</footnote>

<footnote n="14">14 Alexander's polemic against Galen regarding on the first mover is preserved in two partly over-
lapping manuscripts Istanbul Carullah 1279 and Escorial 798; the texts are edited and translated by N.
Rescher and M. E. Marmura, *The Refutation by Alexander of Aphrodisias of Galen's Treatise on the Theory
of Motion* (Islamabad: Islamic Research Institute 1965).</footnote>

<footnote n="15">15 This is reported by Ibn al-Nadīm, *Kitāb al-Fihrist* 7.1 (253 Flügel), referring to Alexander's treatise against Galen on time and place. See also E3.</footnote>

<footnote n="16">16 A. Badawī, *Commentaires sur Aristote perdus en grec et autres epitres*, Beirut 1971, 19–24. The text is preserved in the Arabic manuscript Tashkent 2385. For its supposed connection with Alexander’s polemical treatise against Galen, see R. W. Sharples, “Alexander of Aphrodisias, *On Time*,” *Phronesis* 27 (1982), pp. 58–81, here pp. 72–73; P. Adamson, “Galen and al-Rāzī on Time,” in R. Hansberger, M. A. al-Haytham and C. Burnett (eds.), *Medieval Arabic Thought: Essays in Honour of Fritz Zimmermann* (London: Warburg Institute 2012), pp. 1–14, here p. 6 and n. 28; A. Lammer, *The Elements of Avicenna’s Physics: Greek Sources and Arabic Innovations* (Berlin/Boston: de Gruyter 2018), pp. 23–24. See, however, S. Pines, “A Tenth Century Philosophical Correspondence,” *Proceedings of the American Academy for Jewish Research* 24 (1955), pp. 103–136, here pp. 111–112 n. 43, according to whom everything points to these works not being identical. G. Théry, who edited Gerard of Cremona’s Latin translation of *On time*, suggests that it could have been an excerpt from Alexander’s *Physics* commentary: see G. Théry, *Autour du décret de 1210: II, Alexander d’Aphrodise, Aperçu sur l’influence de sa noétique* (Kain: Le Saulchoir 1926), p. 97.</footnote>
Other fragments of Alexander's polemic against Galen have been preserved in Arabic.<fnref n="17" />

None of these reports and translations refer to Galen's *Dem*. Nevertheless, it is significant that the main topics of these polemics – time, place, and the unmoved mover – were all discussed in that treatise. For time, there is evidence in Simplicius (E1a), which – as is generally accepted – extends also to place. There is no evidence that Galen dealt with these issues anywhere else, and so it is almost certain that Alexander's background text was *Dem*.<fnref n="18" /> The situation is somewhat different with the unmoved mover, since Galen wrote a separate treatise on this topic, and Alexander may have drawn his arguments from that work.<fnref n="19" />

Alexander's treatise *On time* responds to various anonymous objections against Aristotle's definition of time as “the number of motion with respect to the earlier and the later”. Irrespective of whether it forms part of Alexander's polemic against Galen about time and place mentioned by Ibn al-Nadīm, the very fact that Alexander wrote that polemic makes it plausible to suppose that some of the objections addressed in *On time* are Galen's. Some of them do in fact resemble Galen's objections against Aristotle's definition of time in E1–E4.<fnref n="20" /> If they do go back to Galen, then their source is most likely *Dem*. We regard the Galenic provenance of these passages as less certain than in the case of B6* and B7*. Nonetheless, it is plausible enough in our view to merit their inclusion as presumed testimonia in section E.

## Themistius (317-ca. 388)

Themistius mentions Galen three times in his paraphrase of the fourth book of Aristotle's *Physics*, citing and criticising Galen's polemic against Aristotle on time and place (E1, E2, E6). Unlike Simplicius, who refers to *Dem.* in a parallel passage (E1a), Themistius never cites the source of his information. As noted by R. B. Todd, his paraphrase generally appears to be “fairly close” to Alexander of Aphrodisias' *Physics* commen-

<footnote n="17">17 Cf. A. Pietrobelli, “Galen’s Early Reception (Second–Third Centuries),” in P. Bouras-Vallianatos and B. Zipser (eds.), *Brill’s Companion to the Reception of Galen* (Leiden: Brill 2019), pp. 11–38, here pp. 21–22.</footnote>

<footnote n="18">18 Cf. H. B. Gottschalk, “Aristotelian Philosophy in the Roman World from the Time of Cicero to the End of the Second Century A.D.,” in W. Haase (ed.), *Aufstieg und Niedergang der Römischen Welt* II.36.2 (Berlin/New York: de Gruyter 1987), pp. 1079–1175, here p. 1168; M. Rashed, “Alexandre d’Aphrodisse et la ‘Magna Quaestio’.” Rôle et indépendance des scholies dans la tradition byzantine du corpus aristotélicien,” *Les études classiques* 63 (1995), pp. 295–351, here pp. 322–323.</footnote>

<footnote n="19">19 See further below, pp. 59–60.</footnote>

<footnote n="20">20 See R. Chiaradonna, “Le traité de Galien *Sur la démonstration* et sa postérité tardo-antique,” in R. Chiaradonna and F. Trabattoni (eds.), *Physics and Philosophy of Nature in Greek Neoplatonism* (Leiden: Brill 2009), pp. 43–77, here p. 56 n. 65; Adamson, “Galen and al-Rāzī on Time,” pp. 6–7; Sharples, “Alexander of Aphrodisias, *On Time*,” pp. 64–66. See further below, pp. 56–57.</footnote>
tary,<fnref n="21" /> and it seems a reasonable guess that his knowledge of Galen is mediated by Alexander.<fnref n="22" />

## Nemesius (late 4th century)

In his treatise *On the nature of man*, the bishop of Emessa refers to Galen or his works numerous times.<fnref n="23" /> These references include one precious quotation from the third book of *Dem.* (B2) and a testimonium regarding ἀποδεικτικοὶ λόγοι, which arguably concerns the same treatise and the same book (B5).<fnref n="24" />

## Simplicius (ca. 480–560)

Simplicius’ voluminus commentaries on Aristotle contain a mere seven references to Galen, six of them in the *Physics* commentary. One of these probably refers to *Mixtures* (*In Phys.* II.3, 325,23–26 Diels) and the remaining five to passages where Galen criticizes Aristotle on time, place, and the unmoved mover.<fnref n="25" /> Passages on time and place are the same as those quoted by Themistius (E1 and E2); indeed, one of them (E2a) refers to Themistius and his response to Galen’s critique. Yet unlike Themistius, Simplicius specifies that the passage comes from the eighth book of *Dem.*, which indicates that he was not dependent on Themistius for information about it.<fnref n="26" /> Thus he either had direct access to *Dem.* or knew about it through a different intermediary. Since he quotes exactly the same passages as Themistius, and does not refer to *Dem.* anywhere else in his works, it appears more likely that he quotes these passages from an intermediate source, probably the same source that Themistius himself used. Once again, Alexander is the most plausible candidate.<fnref n="27" /> As far as the passage on the unmoved mover is concerned, Simplicius almost certainly quotes it from Alexander, whose response to Galen’s criticism

<footnote n="21">21 Cf. R. B. Todd, “Introduction,” in R. B. Todd, *Themistius on Aristotle Physics 4* (London: Bloomsbury 2003), pp. 1–5, here p. 2.</footnote>

<footnote n="22">22 See Rashed, “Alexandre d’Aphrodise et la ‘Magna Quaestio’,” pp. 322–323; Chiaradonna, “Le traité,” p. 57 with n. 66.</footnote>

<footnote n="23">23 Cf. R. W. Sharples and P. J. van der Eijk, “Introduction,” in R. W. Sharples and P. J. van der Eijk, *Nemesius On the Nature of Man* (Liverpool: Liverpool University Press 2008), pp. 1–32, here pp. 12–13; P. Bouras-Vallianatos, “Galen in Byzantine Medical Literature,” in P. Bouras-Vallianatos and B. Zipser (eds.), *Brill’s Companion to the Reception of Galen* (Leiden: Brill 2019), pp. 86–110, here pp. 86–88.</footnote>

<footnote n="24">24 See below, pp. 35–37.</footnote>

<footnote n="25">25 E1a, E2a, E6a. For the unmoved mover, see Simplicius, *In Phys.* VII.1 (1039,13–15 Diels); the passage is quoted below, p. 60 n. 276.</footnote>

<footnote n="26">26 Cf. Chiaradonna, “Le traité,” p. 54.</footnote>

<footnote n="27">27 For Simplicius’ use of Alexander, see S. Menn, *Simplicius On Aristotle Physics 1–8: General Introduction to the 12 Volumes of Translations* (London et al.: Bloomsbury 2022), pp. 13–14. For Alexander as the</footnote>
immediately follows. It is an open question whether the testimonium goes back to *Dem.*
or to Galen's separate treatise about the unmoved mover.<fnref n="28" />

Alexandrian Neoplatonists (6th century)

Simplicius’ knowledge of *Dem.* seems to depend on the commentary tradition on Aris-
totle’s *Physics*, most probably Alexander of Aphrodisias. There is no other mention of
*Dem.* among the Athenian Neoplatonists. In contrast, there are several indications that
the treatise, or its parts, was available in the Alexandrian Neoplatonist school in the 6th
century. There is an extensive quotation from book four in John Philoponus (C4). There
is also a reference to *Dem.* in the anonymous treatise *All the kinds of syllogism* (F4),
preserved in Parisinus graecus 2064, a 10th–11th-century manuscript containing, among
other texts, Ammonius’ commentary on *Prior analytics*. Jonathan Barnes and Benjamin
Morison, who have recently reedited the text, suggest that “it is a sequence of extracts
from an essay which was written in the ‘school of Ammonius’. That essay,” they add,
“was itself derivative, some of it at least coming from much older writings (and notably
from Galen’s *On proof*).”<fnref n="29" /> Next, there is a puzzling note in ‘Elias’, a 6th-century commen-
tator from the school of Olympiodorus, according to which Galen reduced the number
of Aristotelian categories to five (A30). Elias’ testimonium has no parallel in Galen’s
extant works and its veracity has been questioned.<fnref n="30" /> Yet Elvira Wakelnig has drawn our
attention to a passage in Ibn al-Ṭayyib’s commentary on the *Categories* (11th century),
where a similar reduction is attributed to Galen and specifically linked to *Dem.* (A29).
We may add that three other reports of Galen’s views, which cannot be traced back to
any known work, are found in the Alexandrian Neoplatonists. Two of them appear in
David’s commentary on Porphyry’s *Isagoge* and one in Olympiodorus.<fnref n="31" /> It is possible
(and there are some inconclusive indications to this effect) that some of them at least
go back to *Dem*.<fnref n="32" />

<footnote>source of both Themistius and Simplicius, see Rashed, “Alexandre d’Aphrodise et la ‘Magna Quaestio’,”
pp. 322–323; Chiaradonna, “Le traité,” p. 57 and n. 66.</footnote>

<footnote n="28">28 See further below, pp. 59–60.</footnote>

<footnote n="29">29 J. Barnes and B. Morison, *Galen, Introduction to Logic*, forthcoming with Oxford University Press.
The quotation is from the introduction to the Appendix, which includes the edition and commentary of
*All the kinds of syllogism*.</footnote>

<footnote n="30">30 See C. Prantl, *Geschichte der Logik im Abendlande*, II (Leipzig: S. Hirzel 1855), p. 564; I. von Müller, “Über Galens Werk vom wissenschaftlichen Beweis,” *Abhandlungen der königlichen bayerischen Akademie der Wissenschaften, philosophisch-historische Klasse* 20 (1895), pp. 403–478, here p. 451.</footnote>

<footnote n="31">31 David, *In Porph. Isag.* 19 (154,30–31 Busse) and 21 (163,22–24 Busse); *Olympiodorus, Proleg.* 1 (4,15–18 Busse).</footnote>

<footnote n="32">32 See below, pp. 48–50.</footnote>
## Ḥunayn ibn Isḥāq (809–873)

Ḥunayn ibn Isḥāq was the main translator of Galen's treatises from Greek into Syriac and to Arabic.33 He is the author of the Syriac translation of *Dem.*, which was then translated into Arabic in his circle. In his *Epistle*, a text he wrote to outline the translations of Galen that were produced in his circle or that he knew of, he sheds light on the complex transmission of *Dem*. in Arabic.34 Apparently, in spite of Ḥunayn's continuous efforts, *Dem*. has never been made available to Arabic readers in its entirety.

## Isḥāq ibn ‘Alī al-Ruhāwī (9th century)

Al-Ruhāwī was a 9th-century physician, described by Ibn Abī Uṣaybi'a in his book *Classes of physicians* as well-versed in the Galenic corpus. He mentions the treatise *The conduct of the physician* (*Adab al-ṭabīb*),35 from which our two testimonia are extracted,36 as well as several compendia of Galenic texts. *The conduct of the physician*, the only text to survive, is a deontological treatise which sets out certain rules of conduct and generally describes the behaviour expected, and the knowledge required, of the physician.

## Abū Bakr al-Rāzī (865–925)

Until recently, the majority of the Arabic fragments of *Dem*. had been extracted from Abū Bakr al-Rāzī's *Doubts about Galen*, a medico-philosophical treatise in which Rāzī engages with around a hundred passages from more than twenty Galenic treatises, on topics ranging from the eternity of the world to the different types of pulse.37

Rāzī is a central figure in the history of Islamic philosophy and science. Whereas his medical treatises are well preserved and bear witness to his thorough knowledge

<footnote n="33">33 See for example U. Vagelpohl, “The User-Friendly Galen: Ḥunayn ibn Isḥāq and the Adaptation of Greek Medicine for a New Audience,” in P. Bouras-Vallianatos and S. Xenophontos (eds.), *Greek Medical Literature and Its Readers. From Hippocrates to Islam and Byzantium* (Abingdon/New York: Routledge 2018), pp. 113–130.</footnote>

<footnote n="34">34 Ḥunayn ibn Isḥāq, *Epistle on what was translated* 115 (47–48 Bergsträsser) = A2.</footnote>

<footnote n="35">35 For a full translation of this treatise, see M. Levey, “Medical Ethics in Medieval Islam, with Special reference to al-Ruhāwī’s ‘Practical Ethics’,” *Transactions of the American Philosophical Society, n.s.* 57.3 (1967), pp. 1–100, here pp. 18–97.</footnote>

<footnote n="36">36 We wish to thank Elvira Wakelnig for alerting us to these two passages.</footnote>

<footnote n="37">37 See P. Koetschet, *Abū Bakr al-Rāzī: Doutes sur Galien. Introduction, édition et commentaire* (Berlin/Boston: de Gruyter 2019). The testimonia have been collected in G. Strohmaier, “Bekannte und unbekannte Zitate in den Zweifeln an Galen des Rhazes,” in K.-D. Fischer, D. Nickel, and P. Potter (eds.), *Text and Tradition: Studies in Ancient Medicine and its Transmission Presented to Jutta Kollesch* (Leiden: Brill 1998), pp. 263–287, here pp. 271–274. See further below, pp. 16–17 and 79–83.</footnote>
of Galenic texts, the same cannot be said of his philosophical and theological ideas. However, previous scholarship has shown that Galen's writings, and in particular *Dem.* and *UP*, also had a pervasive presence in Rāzī's philosophical ideas.<fnref n="38" /> In the opening section of the *Doubts*, Rāzī describes *Dem.* as “the most exalted and the most useful of the books, after those sent by God”.<fnref n="39" /> In sections 2 to 6, he quotes *Dem.* in relation to various philosophical topics, going from the demonstration of the eternity of the world to the first substrate (G3), time and void (G6), and vision (G11, G13, G16, G18–G22).

Rāzī's engagement with *Dem.* is not limited to the *Doubts*. According to Bīrūnī, he was also the author of several books on logic, among which a *Book on demonstration (Kitāb al-Burhān)*, as well as a *Book on how sign-inference proceeds (Kitāb fī Kayfīya al-istidlāl).*<fnref n="40" /> Both are lost, but some fragments re-emerged in Ğābir ibn Ḥayyān's *Kitāb al-Taṣrīf* that probably comes from Rāzī's *Kitāb al-Burhān*, where references to *Dem.* were also made.<fnref n="41" />

## Ps.-Ğābir ibn Ḥayyān (9ᵗʰ–10ᵗʰ centuries)

Four testimonia of *Dem.* have been identified in what is known as “the Ğābirian corpus”. In his monumental work,<fnref n="42" /> Paul Kraus has reevaluated the traditional historiography of Ps-Ğābir ibn Ḥayyān and showed that this corpus was, in fact, the work of several authors, most probably alchemists. According to him, the earliest works of Ps.-Ğābir may be placed in the first half of the 9th century, and by the end of the 10th century, the whole collection was established.<fnref n="43" />

Two fragments (C8 and F8) are found in the *Book of morphology* (*Kitāb al-Taṣrīf*). According to our previous research, these fragments are quotations from a logical treatise by Rāzī.<fnref n="44" /> This conclusion is in line with Kraus’ dating, which dates the *Book of balances*, the collection to which the *Book of morphology* belongs, at the beginning of the 10th century.<fnref n="45" />

<footnote n="38">38 P. Adamson, *Al-Rāzī (Oxford: Oxford University Press 2021); Koetschet, Abū Bakr al-Rāzī: *Doutes sur Galien*, pp. xi–cxxxii.*</footnote>

<footnote n="39">39 Rāzī, *Doubts* 2.1 (6,15–17 Koetschet) = A3.</footnote>

<footnote n="40">40 Al-Bīrūnī, *Epistle on Abū Bakr al-Rāzī’s Writings*, p. 14 Kraus.</footnote>

<footnote n="41">41 P. Koetschet, “Abū Bakr al-Rāzī et le signe. Fragment retrouvé d’un traité logique perdu,” *Arabic Sciences and Philosophy* 27 (2017), pp. 75–114.</footnote>

<footnote n="42">42 P. Kraus, *Jābir ibn Ḥayyān. Contribution à l’histoire des idées scientifiques dans l’Islam*, I–II (Cairo: L’Institut français d’archéologie orientale 1942–1943).</footnote>

<footnote n="43">43 Kraus, *Jābir ibn Ḥayyān*, I, p. LXV.</footnote>

<footnote n="44">44 See note 41.</footnote>

<footnote n="45">45 On the datation of the *Book of balances*, see Kraus, *Jābir ibn Ḥayyān*, II, p. vii. For a discussion of the chronological relation between Rāzī’s and Jābir’s writings, see Kraus, *Jābir ibn Ḥayyān*, I, pp. LX–LXII.</footnote>
The other two testimonia by Ps.-Ğābir (E7 and E8) are found in the *Book of research (Kitāb al-Baḥt)*, an extensive treatise devoted to the justification of theurgy.<fnref n="46" /> According to Kraus, it is one of the last treatises of the corpus.<fnref n="47" /> In F10, Ps.-Ğābir mentions both Galen's book *On the first mover* – also lost – and *Dem*. A few pages later, he quotes a longer passage from *Dem*. Kraus believes that these testimonia were mediated by an intermediary source – something that is frequent in the Ğābirian corpus. Moreover, as already mentioned, the two testimonia of *Dem*. found elsewhere in the corpus come from a source other than Galen, namely Rāzī. Kraus suggests Alexander of Aphrodias' treatise *Response to Galen's attack on Aristotle's view that everything that moves is moved by something*, which is lost in Greek but was found and edited in Arabic after Kraus' death.<fnref n="48" /> However, we have not been able to locate a parallel passage in this treatise, although the context is similar. Another possible source is Alexander's commentary on *Physics* VII – lost in Greek and Arabic. Two scholia of the collection gathered and studied by Marwan Rashed evoke respectively the controversy with Galen on the first mover, and the argument ascribed to Plato that the first mover is moved.<fnref n="49" />

## Abū Naṣr al-Fārābī (ca. 873–950)

Abū Naṣr al-Fārābī stands out as one of the most prominent medieval Arabic philosophers, and the best-known representative of the ‘Aristotelian turn’ taken by Arabic philosophy in the wake of the 10th century. He was a member of the ‘School of Baghdad’ which was primarily concerned with the commentaries and the teachings of the Aristotelian logical corpus. Galen, as a philosopher and a logician – and specifically his *Dem*. – represented an obstacle in the way of the Aristotelian movement. However, this did not prevent Galen’s works from being extensively studied by Fārābī.<fnref n="50" />

One of Fārābī's major contributions was his systematic exposition of Aristotle's *Organon* (including the *Rhetoric* and the *Poetics*) in treatises of various kinds. First, he wrote long commentaries, of which unfortunately only the *Long commentary on De interpretatione* survives in an extant form.<fnref n="51" /> Of his short commentaries, we have access to an extensive version of his *Short commentary on De interpretatione* and the

<footnote n="46">46 On this treatise, see Kraus, *Jābir ibn Hayyān*, I, pp. 142–146.</footnote>

<footnote n="47">47 Kraus, *Jābir ibn Hayyān*, I, p. 144.</footnote>

<footnote n="48">48 See Rescher and Marmura, *The Refutation by Alexander*.</footnote>

<footnote n="49">49 M. Rashed, *Alexandre d'Aphrodise, Commentaire perdu à la Physique d'Aristote (Livres IV–VIII): Les Scholies Byzantines. Édition, Traduction et Commentaire* (Berlin/Boston: de Gruyter 2011), pp. 424–427 and 428–429.</footnote>

<footnote n="50">50 See F. Zimmermann, “Al-Fārābī und die philosophische Kritik an Galen von Alexander zu Averroes,” in A. Dietrich (ed.), *Akten des VII. Kongresses fur Arabistik und Islamwissenschaft, Göttingen, 15. bis 22. August 1974* (Göttingen: Vandenhoeck & Ruprecht 1976), pp. 401–414.</footnote>

<footnote n="51">51 It was translated and published by F. Zimmermann along with the short commentary on the same</footnote>
*Short commentary on the Prior analytics.*<sup>52</sup> Of his other commentaries, only fragments or indirect sources exist. The remaining fragment of his *Long commentary on the Prior analytics* was edited and published by Daneshpazuh.<sup>53</sup> According to the Alexandrian scheme followed by Fārābī, the heart of logic lay in the science of demonstration, as expounded in the *Posterior analytics*.

Four testimonia of our collection go back to Fārābī. Two of them are found directly in Fārābī's treatises (F10 and F11) and two are mediated by Maimonides (F12) and Ibn Rušd (C16), respectively.<sup>54</sup>

## Ibn Abī Saʿīd al-Mawṣilī, via Yaḥyā ibn ʿAdī (873–974)

A passage on Galen's conception of time is found in a correspondence between Ibn Abī Saʿīd al-Mawsilī and the well-known philosopher of Baghdad Yaḥyā ibn ʿAdī (873–974). In this correspondence, which was first studied by Shlomo Pines,<sup>55</sup> the former asked the latter to give his opinion on various issues in Aristotle's *Physics*. Their discussion involved a criticism attributed to Galen of Aristotle's definition of time, with a reference to Alexander's *Treatise against Galen on time and place* (E3).<sup>56</sup>

## Abū al-Ḥassan Aḥmad b. Muḥammad al-Ṭabarī (d. around 985)

One testimonium is found in a handbook called *Hippocratic treatments* (Al-Muʿlağāt al-Buqrāṭīya), which was composed around 950. It is attributed to Abū al-Ḥassan Aḥmad b. Muḥammad al-Ṭabarī, a physician in the service of the Buyid ruler Rukn al-Dawla (r. 936–972).<sup>57</sup> This handbook is composed of ten books, further divided into chapters. Our testimonium is located in the introductory book, where the author aims to reinforce the scientific framework of his work. Books 2 to 10 deal with the diseases of the human body, presented traditionally from the head downwards. Throughout the handbook,

<footnote>treatise: F. Zimmermann, *Al-Fārābī's Commentary and Short Treatise on Aristotle's De interpretatione* (London: Oxford University Press 1981).</footnote>

<footnote n="52">52 N. Rescher, *Al-Fārābī's Short Commentary on Aristotle's Prior Analytics* (Pittsburgh: University of Pittsburgh Press 1963).</footnote>

<footnote n="53">53 Fārābī, *Al-Manṭiqyāt lil-Fārābī*, II, pp. 263–553 Daneshpazuh.</footnote>

<footnote n="54">54 See further below, pp. 84–85.</footnote>

<footnote n="55">55 Pines, “A Tenth Century Philosophical Correspondence.”</footnote>

<footnote n="56">56 Alexander's treatise is also mentioned in Ibn al-Nadīm, *Kitāb al-Fihrist* 7.1 (253 Flügel) = 2.609 Dodge. On this, see below, pp. 54–56.</footnote>

<footnote n="57">57 We wish to thank Elvira Wakelnig for drawing our attention to this testimonium.</footnote>
al-Tabari makes many references to previous physicians, and in particular to Galen, who is the most quoted author.<fnref n="58" />

## Ibn al-Ṭayyib (980–1043)

A logical passage from *Dem.* was transmitted by Ibn al-Ṭayyib.<fnref n="59" /> Abū al-Ḥarağ ‘Abdallah ibn al-Ṭayyib is one of the last representatives of scholars who, following Mattā ibn Yūnus and Yaḥyā ibn ‘Adī, wrote commentaries on Aristotle’s works by studying the Greek commentaries of Late Classical Antiquity (Porphyry, Ammonius, Olympiodorus, Simplicius, Philoponus, and Elias). His testimonium of *Dem.* has a parallel in Elias, but neither its (somewhat puzzling) content nor the context in which it is preserved indicates that Elias is its source. Although Ibn al-Ṭayyib is thought to be the author of a commentary of the entire *Organon*, only his commentary of the *Categories*, as well as a summary of the commentary of the *Posterior analytics*, have been preserved.<fnref n="60" />

## Abū Saʿīd ‘Ubaydallah ibn Buḥṭīšū’ (980–1060)

Our only testimonium mentioning book eleven comes from a treatise entitled *On the fact that the physician has to consider the states of the soul and that love is an illness*, by Abū Saʿīd ‘Ubaydallah ibn Buḥṭīšū’. One of the last representatives of the Buḥṭīšū’ family, a famous line of physicians, Abū Saʿīd ‘Ubaydallah ibn Buḥṭīšū’ is the author of very few treatises, even fewer of which have been edited. In the above-mentioned treatise, Ibn Buḥṭīšū’ collects a large number of quotations from Hippocrates, Plato, Aristotle, and Galen.

## Abū al-‘Alā’ ibn Zuhr (d. 1130)

In addition to the testimonia from Rāżī’s *Doubts*, which were already known, this collection provides us with over twenty hitherto unpublished passages coming from another and more detailed source related to the *Doubts*, namely the *Solution to the Doubts about*

<footnote n="58">58 For a review of all the references in the treatise, see L. Ambjörn, “Book-Titles Mentioned in the 10th Century Medical Encyclopaedia Mu’ālağāt al-Buqrātīya,” *Galenos, Rivista di filologia dei testi medici antichi* 5 (2011), pp. 103–111.</footnote>

<footnote n="59">59 Again, we owe this information to Elvira Wakelnig, who also kindly provided us with the translation of the testimonium and its immediate context.</footnote>

<footnote n="60">60 C. Ferrari, “Ibn al-Ṭayyib,” in H. Lagerlund (ed.), *Encyclopedia of Medieval Philosophy* (Dordrecht: Springer 2011).</footnote>
Galen by Abū al-‘Alā’ ibn Zuhr.<fnref n="61" /> Abū al-‘Alā’ ibn Zuhr was a doctor who lived in 12th-cen-
tury Cordoba. He belonged to a family of physicians, the Banu Zuhr, and was the father
of the well-known ‘Abd al-Malik ibn Zuhr (Avenzoar).<fnref n="62" /> He wrote several medical trea-
tises, among which the *Solution*. Responding to Rāzī’s *Doubts* had become a genre in
itself: Ibn Abī Ṣādiq, Ibn Riḍwān, Abū al-‘Alā’ ibn Zuhr, and ‘Abdul-Laṭīf al-Baġdādī each
authored a treatise also called *Solution to the Doubts about Galen*. However, the treatise
by Abū al-‘Alā’ is the only one that has come down to us.<fnref n="63" /> In his *Solution*, Abū al-‘Alā’s
main line of defense against Rāzī – called “The Sophist” throughout the book – is that
the latter gives a biased account of what Galen says. This prompts Abū al-‘Alā’ to system-
atically give a quotation of the same passage which he claims to be literal. Wherever we
could compare Abū al-‘Alā’s quotations with Arabic translations of the same passages,
we found that his rendering was indeed very close to the source.

The *Solution* is divided into “questions” (*mas’ala*), each of them starting with a quo-
tation from the *Doubts*, preceded by “the Sophist said” (*qāla al-sūfīṣṭā’ī*). As Abū al-‘Alā’
explains in the introduction, he cannot admit that Rāzī is indeed the author of these
*Doubts*, considering how shameful they are. Interestingly, Abū al-‘Alā’’s quotations are
introduced in defense of Galen and not in a polemical context, which is not true of most
of our Arabic testimonia. In addition to enriching our knowledge of *Dem*. itself, Abū
al-‘Alā’ provides us with additional information on the Arabic reception of *Dem*.<fnref n="64" />

Ibn Bāğğa (1085–1138)

Ibn Bāğğa is a later source to *Dem*. Like Abū al-‘Alā’, Ibn Rušd, and Maimonides, he is an Andalusian philosopher. He wrote a *Commentary on Aristotle’s Physics*, where he refers to Galen’s theory of time (see E4).<fnref n="65" /> Unlike Abū al-‘Alā’, his testimonium of *Dem*. does not seem to come from a direct reading of the treatise but depends ultimately on Alexander of Aphrodisias.

<footnote n="61">61 Edition of the treatise is under preparation by Pauline Koetschet and Iktimal Rajab.</footnote>

<footnote n="62">62 To distinguish Abū al-‘Alā’ ibn Zuhr from his son, we refer to him either by the full name or as “Abū al-‘Alā” in this book.</footnote>

<footnote n="63">63 Fragments of Ibn Abī Ṣādiq’s treatise survive through an indirect tradition.</footnote>

<footnote n="64">64 See below, pp. 72–74.</footnote>

<footnote n="65">65 P. Lettinck, *Aristotle’s Physics and Its Reception in the Arabic World: With an Edition of the Unpublished Parts of Ibn Bajja’s Commentary on the Physics* (Leiden/New York: Brill 1994).</footnote>
### Ibn al-Ṣalāḥ (1090–1153)

One mention of *Dem.* (F1) is found in the introduction to the logical treatise *On the fourth figure of the categorical syllogism attributed to Galen* by Ibn al-Ṣalāḥ, a Persian physician and mathematician.<fnref n="66" />

### Ibn Rušd (1126–1198)

Ibn Rušd (Averroes), among many other achievements, was a prolific commentator of Aristotle, which led him to engage occasionally and indirectly with *Dem.* Two testimonia in this volume come from his commentaries. In the first (C16), he quotes Fārābī as his source, whereas the second (E1b) seems to be based on the Greek commentary tradition.

### Maimonides (1138–1204)

Maimonides is an indirect witness to *Dem.*, quoting an (otherwise lost) passage from Fārābī's *Long commentary on the Prior analytics*, where *Dem.* is mentioned (F12).<fnref n="67" />

### Albertus Magnus (d. 1280)

The only Latin medieval author in our collection ascribes to Galen an interesting argument about time being in the soul by virtue of the motion of the soul (E1c). However, as shown by U. R. Jeck, this passage is based on Ibn Rušd's *Commentary on Aristotle's Physics*, where a similar argument is associated with Plato, not Galen.<fnref n="68" /> Albertus' "testimonium" thus seems to be the result of a misunderstanding or creative reinterpretation of his source, namely the Latin translation of Ibn Rušd. It was probably inspired by E1b.

<footnote n="66">66 The treatise is edited and translated in N. Rescher, *Galen and the Syllogism* (Pittsburgh: Pittsburgh University Press 1966), pp. 52–87. On the Arabic debate on the fourth figure of the syllogism, see below, p. 87.</footnote>

<footnote n="67">67 See above, pp. 11–12 (on Fārābī).</footnote>

<footnote n="68">68 See U. R. Jeck, *Aristoteles contra Augustinum: Zur Frage nach dem Verhältnis von Zeit und Seele nach den antiken Aristoteleskommentatoren, im arabischen Aristotelismus und im 13. Jahrhundert* (Amsterdam/Philadelphia: B. R. Grüner 1994), pp. 245–249.</footnote>
## 2 Modern scholarship

### The sources

The history of the modern debate on *Dem.* is closely linked to the gradual discovery of the relevant sources. In his monumental edition of Hippocratic and Galenic works published in the 17th century, René Chartier included testimonia found in Nemesius (B2, B5), John Philoponus (C4), Simplicius (E1a, E2a, E6a), and Ibn Rušd (C16, E1b).<fnref n="69" /> In his 1869 monograph on *Al-Fārābī*, Moritz Steinschneider cited passages from *Hunayn* (A2), Ibn Rušd (C16), and Maimonides (F12).<fnref n="70" /> But a decisive breakthrough came in 1895, when Iwan von Müller published his study “Über Galens Werk vom wissenschaftlichen Beweis”.<fnref n="71" /> Von Müller’s aim was not simply to collect the available testimonia, but to reconstruct the actual contents and argument of the lost treatise. He collected thirty-one passages from Galen, nine from later Greek sources (Nemesius, Themistius, Simplicius, and Philoponus) and five from Arabic sources.<fnref n="72" /> However, he does not present them as a collection of numbered texts; instead, he embeds them directly in the main text of his dense prose or cites them in footnotes alongside parallels and other relevant passages from the Galenic corpus.

Von Müller’s study remains the only attempt to date to assemble all the available testimonia in one place, but the amount of relevant material has significantly increased, especially in the last few decades. In 1998 Gotthard Strohmaier published, in German translation, citations from Galen’s works in Abū Bakr al-Rāzī’s *Doubts about Galen*. He listed over twenty citations from *Dem.*, which mostly come from the fourth and the thirteenth books of the treatise.<fnref n="73" /> This line of inquiry has been followed by Pauline Koetschet, who edited the Arabic text of Rāzī’s *Doubts* and discovered a wealth of other

<figure><img src="image_10.png" /></figure>

<footnote n="69">69 R. Chartier, *Opera Hippocratis Coi et Galeni Pergameni, medicorum omnium principum*, II (Paris 1638), pp. 59–60 (Philoponus), 67–68 (Simplicius), and 70–71 (Ibn Rušd); vol. V (Paris 1639), pp. 1–3 (Nemesius). Chartier does not link all these quotations with *Dem.*, often calling them simply “fragments”.</footnote>

<footnote n="70">70 M. Steinschneider, *Al-Farabi (Alpharabus): Des arabischen Philosophen Leben und Schriften* (St.-Pétersbourg: L’Académie Impériale des Sciences 1869), pp. 27, 32–33, and 134.</footnote>

<footnote n="71">71 *Abhandlungen der königlichen bayerischen Akademie der Wissenschaften, philosophisch-historische Klasse* 20 (1895), pp. 403–478.</footnote>

<footnote n="72">72 Apart from A2, C16, E1b, and F12 already mentioned, von Müller adds G30, citing personal communication with Steinschneider. Von Müller quotes the Arabic material in Latin or Steinschneider’s German translations.</footnote>

<footnote n="73">73 G. Strohmaier, “Bekannte und unbekannte Zitate in den Zweifeln an Galen des Rhazes,” in K.-D. Fischer, D. Nickel and P. Potter (eds.), *Text and Tradition: Studies in Ancient Medicine and its Transmission Presented to Jutta Kollesch* (Leiden: Brill 1998), pp. 263–287, here pp. 271–274. Strohmaier lists 24 citations, but one of them is misattributed, as it refers to Aristotle rather than Galen (S. 9,20 on p. 272), and two others are Rāzī’s interpretations, rather than citations (S. 11,2–4 on p. 273 and S. 14,9f. on p. 274).</footnote>
material in a previously unpublished response to it by Abū al-‘Alā’ ibn Zuhr.<fnref n="74" /> Abū al-‘Alā’ covers more or less the same parts of *Dem.* as Rāzī, but adds a number of illuminating details.

Arabic sources have also yielded more information about the discussion of time which, as we know from Simplicius, was located mainly (if not exclusively) in the eighth book of *Dem.* Already in 1955, Schlomo Pines drew attention to Yaḥyā ibn ‘Adī’s reference to Galen’s polemic against Aristotle’s definition of time (E3).<fnref n="75" /> The passage refers to Alexander (probably of Aphrodisias) as its source and includes details about Galen’s position unknown from the Greek commentators. It has been studied in connection with their reports, as well as with Alexander’s *On time*, by specialists on the reception history of Aristotle’s *Physics*.<fnref n="76" /> This research is of course of paramount importance for the study of *Dem*.<fnref n="77" /> For, although it is never mentioned in these sources, *Dem.* was almost certainly where Galen’s polemic took place.<fnref n="78" /> In his attempt to reconstruct Galen’s precise position regarding time (and its possible influence on Rāzī’s notion of absolute time), Peter Adamson takes account of all the material just mentioned and adduces two further parallels from Arabic sources (E1b and E4).

Yet Greek texts have also delivered new information. Studies on the so-called eighth *Stromateus* (*Liber logicus*) by Clement of Alexandria have drawn attention to the relevance of this text to the enquiry about Galen’s method, and specifically about *Dem*.<fnref n="79" /> In 2011, one of us advanced the hypothesis that two sections in particular (β and γ of *Lib*.

<footnote n="74">74 P. Koetschet, *Abū Bakr al-Rāzī: Doutes sur Galien. Introduction, édition et commentaire* (Berlin/Boston: de Gruyter 2019); eadem, “Galien, al-Rāzī, et l’éternité du monde. Les fragments du traité *Sur la démonstration*, IV, dans *Les doutes sur Galien*,” *Arabic Sciences and Philosophy* 25 (2015), pp. 167–198.</footnote>

<footnote n="75">75 S. Pines, “A Tenth Century Philosophical Correspondence,” *Proceedings of the American Academy for Jewish Research* 24 (1955), pp. 103–136.</footnote>

<footnote n="76">76 See esp. M. Rashed, “Alexandre d’Aphrodise et la ‘Magna Quaestio’. Rôle et indépendance des scholies dans la tradition byzantine du corpus aristotélicien.” *Les études classiques* 63 (1995), pp. 295–351, esp. pp. 318–327.</footnote>

<footnote n="77">77 Cf. R. Chiaradonna, “Le traité de Galien *Sur la démonstration* et sa postérité tardo-antique,” in R. Chiaradonna and F. Trabattoni (eds.), *Physics and Philosophy of Nature in Greek Neoplatonism* (Leiden: Brill 2009), pp. 43–77, here p. 56 and n. 65.</footnote>

<footnote n="78">78 Rāzī and Abū al-‘Alā’ ibn Zuhr do in fact locate Galen’s discussion of time in *Dem*. (G6 and G7); however, their statements pertain to the thirteenth book, not to the eighth, which contained the polemic against Aristotle. See below, pp. 66–67.</footnote>

<footnote n="79">79 Cf. W. Ernst, *De Clementis Alexandrini Stromatum libro VIII. qui fertur* (Göttingen: Hubert 1910), pp. 11–24; F. Solmsen, “Early Christian Interest in the Theory of Demonstration,” in W. den Boer, P. G. van der Nat, C. M. J. Sicking and J. C. M. van Winden (eds.), *Romanitas et Christianitas: Studia J.H. Waszink Oblata* (Amsterdam: North-Holland 1973), pp. 281–291; T. Tieleman, *Galen and Chrysippus On the Soul: Argument and Refutation in De placitis, Books II–III* (Leiden/New York/Köln: Brill 1996), esp. pp. 20, 24–25, 30, 104, and 127; M. Havrda, “Galenus Christianus? The Doctrine of Demonstration in *Stromata* VIII and the Question of Its Source,” *Vigiliae Christianae* 65 (2011), pp. 343–375; idem, *The So-Called Eighth Stromateus by Clement of Alexandria: Early Christian Reception of Greek Scientific Methodology* (Leiden: Brill 2016), pp. 34–50.</footnote>
log. = Strom. VIII 2.3.1–5.15.1) draw directly on Dem.; and a commentary on *Liber logicus*, published in 2016, added further support to this view.<fnref n="80" /> The hypothesis has been well received.<fnref n="81" /> Another Greek source for the study of Dem. unknown to von Müller is the above-mentioned anonymous essay *All the kinds of syllogism*, first edited in 1899, which includes at least a reference to, and possibly also extensive material from, Dem.<fnref n="82" />

## Interpretation

Von Müller’s 1895 paper is the most ambitious attempt so far to reconstruct the contents of Dem., their sequence and distribution, and to grasp the overall purpose of the treatise. As far as the purpose is concerned, von Müller explains it in light of Galen’s familiar story of his own education; his frustration at the failure of philosophical schools to justify their doctrines; his salvation from the Pyrrhonic ἀπορία through geometrical proof; and his desire to create, after the model of geometry, a rigorous method of inquiry applicable to medical problems.<fnref n="83" /> For reconstructing the content, von Müller uses three types of source: Galen’s own references and allusions to the treatise; quotations by later authors; and – most controversially perhaps – the list of works written after Dem., in which, as Galen says, he “provides a broader treatment of what was discussed concisely in that work” (A9).<fnref n="84" />

<footnote n="80">80 The argument about these two sections is presented in Havrda, “Galenus Christianus?”; it is summarized and further complemented in idem, *The So-Called Eighth Stromateus*, pp. 34–41.</footnote>

<footnote n="81">81 See, e.g., P. van der Eijk, “Galen and Early Christians on the Role of the Divine in the Causation and Treatment of Health and Disease,” *Early Christianity* 5 (2014), pp. 337–370, here p. 355 n. 47; A. Le Bouluec, “Clément d’Alexandrie,” in G. Dorival and A. Le Boulluec, *L’Abeille et l’Acier: Clément d’Alexandrie et Origène* (Paris: Les Belles Lettres 2019), pp. 13–163, here p. 127 and n. 442; T. Tieleman, “Galen’s Notion of Dialectic,” in R. J. Hankinson and M. Havrda (eds.), *Galen’s Epistemology: Experience, Reason, and Method in Ancient Medicine* (Cambridge: Cambridge University Press 2022), pp. 136–155, here p. 139 n. 10; R. Chiaradonna, *Ontology in Early Neoplatonism: Plotinus, Porphyry, Iamblichus* (Berlin/Boston: de Gruyter 2023), p. 126. At an international workshop dedicated to *Liber logicus*, held in Prague in April 2017 and including, among others, Jonathan Barnes, Riccardo Chiaradonna, Jim Hankinson, Katerina Ierodiakonou, and Teun Tieleman, the participants agreed that the Galen hypothesis was convincing with regard to sections β and γ. As regards the other sections of *Liber logicus*, the Galenic trace was considered less distinct.</footnote>

<footnote n="82">82 See Barnes and Morison quoted above, p. 8.</footnote>

<footnote n="83">83 I. von Müller, “Über Galens Werk vom wissenschaftlichen Beweis,” *Abhandlungen der königlichen bayerischen Akademie der Wissenschaften, philosophisch-historische Klasse* 20 (1895), pp. 403–478, here pp. 414–416. Von Müller’s main point of reference is *Lib. prop.* 14.1–6 (164,1–165,13 Boudon-Millot / 11, 115,21–117,16 von Müller / XIX.39–40 K). The passage immediately precedes A1, being in fact an introduction to, and advertisement of, *Dem*.</footnote>

<footnote n="84">84 Von Müller, “Über Galens Werk,” p. 416, referring to *Lib. prop.* 14.17 (167,14–16 Boudon-Millot / 11, 119,10–12 von Müller / XIX.43 K). The third source was more controversial for von Müller than it is for us. For, based on Ambrisianus Q3, which reads τῶν ἐν ἑκεῖνοις συντόμως εἰρημένων (“what was</footnote>
Von Müller offers a reconstruction of the following books: I–V, VIII, XIII and XIV. All the testimonia available to him are incorporated into this division based on his assumptions about the structure of Galen’s exposition. One of these assumptions is that Galen expounded the theory of demonstration and demonstrative inquiry in a systematic manner, and did so in the early parts of the treatise. In fact, von Müller draws a sharp distinction between two parts of *Dem.*: one (represented by books I–V) where Galen lays the foundations of his theory of scientific knowledge, and another (starting probably with book VIII) where he tests the theory by applying it to problems that famous philosophers and doctors attempted to solve.<fnref n="85" /> But even within the first half, von Müller places all the important elements of the doctrine in the first three books.

This explains the striking discrepancy between the length of von Müller’s analysis of books I–III, and the actual number of testimonia referring to them. Von Müller dedicates more than forty-two pages to this part of the treatise, in contrast to less then sixteen pages covering books IV–XIV.<fnref n="86" /> This is surprising, considering how little information he had about the first three books. There is one brief reference to book one (B1) and one citation from book three (B2), and that is all. For book two, discussed by von Müller over a span of twenty pages, there is not a single testimonium! The explanation of course is that most testimonia do not have accompanying information about their specific location in the text; yet von Müller locates almost all of them in one of the first three books and weaves them – with the help of allusions and parallels in the Galenic corpus – into a coherent argument.

As noted, there are only two reliable clues to reconstructing the contents of the first three books: B1 indicates that the first book was an exhortation to method; and B2 shows that, in the third book, Galen dealt with a case of homonymy in physiology, namely with the ambiguous use of the word καρδία. Von Müller contextualizes B2 in an ingenious manner (which, as we shall see, is largely confirmed by our findings). The upshot of his argument is that, in book three, having presented the general theory of demonstration, Galen turns to the method of solving particular problems. While doing so, von Müller suggests, Galen pursues a similar line of exposition as in *PHP*, distinguishing four types of premisses – scientific, dialectical, rhetorical, and sophistic – and explaining their difference.

As far as the first book is concerned, von Müller believes that, in its exhortative part, it included a critique of those who reason without proof; an exposition of the dis-

<footnote>discussed concisely in those books”), von Müller interprets the passage as referring not to *Dem.*, but rather to Galen’s commentaries, composed in his youth, on the logical works of Aristotle, Theophrastus, Eudemus, and Chrysippus, which are mentioned in the previous sentence; cf. *Lib. prop.* 14.17 (167,6–14 Boudon-Millot / 11, 119,2–18 von Müller / XIX.43 K); von Müller, “Über Galens Werk,” p. 416. However, the ms. Vlatadon 14, followed by Boudon-Millot, reads τῶν ἐν ἑκείνῃ (*scil*. πραγματείᾳ), thus unambiguously referring to *Dem*.</footnote>

<footnote n="85">85 Von Müller, “Über Galens Werk,” pp. 467–468.</footnote>

<footnote n="86">86 Von Müller, “Über Galens Werk,” pp. 417–460 (I–III); pp. 460–476 (IV–XIV).</footnote>
agreement (διαφωνία) among medical schools; and the endorsement of demonstrative expertise as the capacity to recognize what is true and what is false in every doctrine.<fnref n="87" /> In addition (and much less plausibly), von Müller proposes that, in the same book, Galen situated himself with respect to the Peripatetic tradition (cf. A24); provided an outline of the syllogistic theory; criticized syllogisms “by additional assumption” (F5); discussed possible and mixed syllogisms (F9–F12, A9); and different types of syllogisms more generally (A9); dealt with the number of syllogistic figures (F2); and identified the limits of induction (A27, A28).<fnref n="88" />

Von Müller’s account of the second book of Dem. also covers a large number of topics. It starts with epistemology, encompassing the first principles and the criteria of knowledge, the axioms, the relation between reason and experience, the common notions, and scepticism. It continues with complex methodological and metaphysical issues, such as the appropriate starting points of inquiry, notional and essential definitions, division, the categories, form and substance.<fnref n="89" />

Taken together, the first three books, as conceived by von Müller, comprise what he calls Galen’s “positive methodology” (“die positive Methodik”).<fnref n="90" /> They are complemented by books four and five, whose reconstruction covers a mere eight pages. We know that book four dealt with the contested question of the eternity of the world (von Müller cites C1, C4, and C16). For von Müller, this is an example of an issue that cannot be solved in a strictly scientific manner, but only on the basis of plausible premises derived from experience. The fourth book then, he argues, was an essay about the limits of knowledge, which may have also included discussions about the substance of the soul (B5) and embryology (B3) – the latter on account of the mysterious nature of the formative capacity responsible for organogenesis.<fnref n="91" /> The fifth book, which dealt with sense-perception (D1–3), is a supplement to the teaching about the criteria (which include sense-perception) and a “warning”, as von Müller puts it, against erroneous descriptions of the capacities of individual senses.<fnref n="92" />

Whatever the contents of books six and seven were (we know nothing of them), the eighth book, according to von Müller, begins the second half of the treatise, which did not present any theory, but discussed significant philosophical and medical questions and the solutions to them proposed by particular thinkers. In von Müller’s view, the sequence of topics in this part is not determined by their content, but rather by the chronology of thinkers in question. In book eight, where Galen criticizes Aristotle’s definition of time (and probably also place), his opponent is Aristotle, whereas in book

<footnote n="87">87 Von Müller, “Über Galens Werk,” pp. 417–422.</footnote>

<footnote n="88">88 Von Müller, “Über Galens Werk,” pp. 422–430.</footnote>

<footnote n="89">89 Von Müller, “Über Galens Werk,” pp. 430–451.</footnote>

<footnote n="90">90 Von Müller, “Über Galens Werk,” p. 416.</footnote>

<footnote n="91">91 Von Müller, “Über Galens Werk,” pp. 460–465.</footnote>

<footnote n="92">92 Von Müller, “Über Galens Werk,” p. 465.</footnote>
thirteen, dealing with the elements and the physiology of sight (and possibly also in book fourteen, dealing with digestion), it is Asclepiades of Bithynia.<fnref n="93" />

Von Müller's command of Galenic works is impressive and some of his insights about *Dem.* are enduring.<fnref n="94" /> His article continues to be a useful resource for the study of Galen's methodology. However, his attempt to compress all the doctrinal elements into the first three books is unfounded and implausible.<fnref n="95" /> It is unlikely for an introductory treatise addressed primarily to doctors (A8) to start with technical discussions about syllogistics and, given Galen's expansive style of writing and obsession with clarity, it is hard to believe that he would cover so many complex issues in such a small space. Indeed, he emphasizes that he has dealt with these issues "clearly and extensively" (σαφῶς τε ἄμα καὶ διὰ πολλῶν).<fnref n="96" /> Moreover, as we shall see, new findings allow us to locate some of these discussions much later in the treatise.

Another question concerns the presence of problems whose relevance to the theory of demonstration is far from obvious (especially if the theory was supposed to be useful for medical students): the eternity of the world, time and place, the elements, vision, etc. Why are they included, why in this particular order, and how are they relevant to medicine? As we have seen, von Müller proposes that the majority of these topics (i.e. those appearing from book eight on) are test cases for the efficacy of the demonstrative method, and that they are chosen as significant questions to which particular thinkers believed to have provided an answer. The situation is different with book four, in which topics are used to illustrate the limits of scientific knowledge. Commenting on von Müller's reconstruction, Jonathan Barnes notes that "he pays too much attention to those odd items".<fnref n="97" /> Barnes' point is that discussions of such issues as perception, time, and elements could not have been the main agenda of the later books of *Dem.* But he does not offer an alternative explanation of why they were discussed at all. In an important article on *Dem.* – the first study after von Müller to focus exclusively on this treatise – Riccardo Chiaradonna supplements Barnes' criticism with just such an explanation.<fnref n="98" />

<footnote n="93">93 Von Müller, “Über Galens Werk,” pp. 467–468; for book fourteen, see p. 476.</footnote>

<footnote n="94">94 This is particularly true about the dating of *Dem.* and the contents of book 3. Also, von Müller's suggestions about the exhortatory part of the first book are entirely plausible.</footnote>

<footnote n="95">95 Cf. J. Barnes, “Galen on Logic and Therapy,” in R. J. Durling and F. Kudlien (eds.), *Galen's Method of Healing: Proceedings of the 1982 International Galen Symposium* (Leiden: Brill 1991), pp. 50–102, here p. 69 n. 61; Chiaradonna, “Le traité,” pp. 46–47. Chiaradonna suggests that von Müller's interpretation is due to the conventions of philosophical prose of von Müller's own time: a comprehensive theoretical exposition at the beginning being followed by a historical section or an overview of earlier theories.</footnote>

<footnote n="96">96 A27.</footnote>

<footnote n="97">97 Barnes, “Galen on Logic and Therapy,” p. 69 n. 61.</footnote>

<footnote n="98">98 Chiaradonna, “Le traité.”</footnote>
Chiaradonna's starting point is Galen's pragmatic (use-based) approach to logic, a feature already emphasized by Barnes.<fnref n="99" /> For Galen, logic, while constituting a part of philosophy, is a tool to be used by medicine: Galen's epistemology is an applied epistemology, the areas of its application being the study and practice of medicine.<fnref n="100" /> How does this explain the presence of the “odd items” in *Dem.?* Chiaradonna agrees with von Müller that the discussion of vision, for instance, is connected to the doctrine of the criteria. However, rather than seeing it as a supplement to that doctrine, Chiaradonna regards it as a part of its exposition, carried out with particular reference to medicine, on the basis that natural criteria like visual perception are the foundations of scientific knowledge in medicine.<fnref n="101" /> The questions of the eternity of the world or of the substance of the soul serve the purpose of distinguishing between problems that allow for scientific demonstration and those that do not.<fnref n="102" /> Here, Chiaradonna again agrees with von Müller but emphasizes the functionality of these discussions with regard to scientific practice. Likewise, Galen's polemic about time draws attention to the limits of definitions, time being an example of an item that cannot be defined in a strictly scientific manner.<fnref n="103" /> However, if Galen's concern was medicine, we may ask why he turns to more general issues of natural philosophy. Chiaradonna responds that some of these issues (e.g. the theory of the elements) are in fact directly relevant to medicine, whereas others (like the ones mentioned earlier) are useful for “clarifying epistemological problems inherent to medicine”.<fnref n="104" />

Chiaradonna presents a more coherent account of the various issues discussed in *Dem.* than von Müller and integrates them more closely with the agenda of the treatise. Other proposals have been made about the particular choice of these topics, not conflicting with Chiaradonna's explanations, but adding more nuance to them. Referring to the part about the elements in book thirteen, Benjamin Morison notes that *Dem.* “did not just discuss logical theory in the narrow sense of how to construct deductions, but rather discussed which axioms are the correct ones for science”.<fnref n="105" /> According to this

<footnote n="99">⁹⁹ J. Barnes, “Galen and the Utility of Logic,” in J. Kollesch and D. Nickel (eds.), *Galen und das helle-nistische Erbe: Verhandlungen des IV. Internationalen Galen-Symposiums* (Stuttgart: Franz Steiner 1993), pp. 33–52.</footnote>

<footnote n="100">¹⁰⁰ Chiaradonna, “Le traité,” pp. 49–52.</footnote>

<footnote n="101">¹⁰¹ Chiaradonna, “Le traité,” pp. 52–53. We might object that this does not pertain specifically to medicine; nor is the interest in perception peculiar to the pragmatic approach to logic. So the principle of applied epistemology does not really help to explain the presence of this particular issue. Moreover, Chiaradonna does not distinguish between the discussions of vision in books five and thirteen, whose aims were probably different. Nonetheless, in our view his argument that the discussion in book five is part of the exposition about the criteria is convincing.</footnote>

<footnote n="102">¹⁰² Chiaradonna, “Le traité,” p. 54.</footnote>

<footnote n="103">¹⁰³ Chiaradonna, “Le traité,” pp. 60–62.</footnote>

<footnote n="104">¹⁰⁴ Chiaradonna, “Le traité,” p. 59 n. 75.</footnote>

<footnote n="105">¹⁰⁵ B. Morison, “Logic,” in R. J. Hankinson (ed.), *Cambridge Companion to Galen* (Cambridge: Cambridge University Press 2008), pp. 66–115, here p. 74.</footnote>
view, then, Galen's focus on (at least) some of the issues of natural philosophy could be due to his interest in the principles. Finally, in a paper published in 2015, one of us argued that Galen's choice of topics, made for didactic and training purposes, was largely traditional and could have been influenced by a sceptic source similar to the one used by Sextus Empiricus. This could be explained by the anti-sceptic agenda of the treatise and its aim to teach doctors, using illustrative examples, how to hold onto plain phenomena and resist the snares of false reasoning, whether it be sceptic or dogmatic.<fnref n="106" /> We will further refine these suggestions in the next two chapters.

<footnote n="106">106 M. Havrda, "The Purpose of Galen's treatise *On Demonstration*," *Early Science and Medicine* 20 (2015), pp. 265–287.</footnote>
# 3 Title, date, purpose, audience, and genre

## Title

The treatise was called περὶ ἀποδείξεως<fnref n="107" /> and so referred to as τὰ περὶ ἀποδείξεως, where the plural denotes ὑπομνήματα or βιβλία (both referring to “books” in the sense of divisions of the treatise).<fnref n="108" /> Alternatively, Galen inserts the definite article in the title (D1) and refers to the work by its content as: ἡ περὶ τῆς ἀποδείξεως πραγματεία (A1, A6, A8, A9, A12, A14, A17, D3, F5, G27); τὰ περὶ τῆς ἀποδείξεως ὑπομνήματα (A16, A22, A24, A28, G1) or βιβλία (A17); or αἱ περὶ τῆς ἀποδείξεως μεθόδοι (A21, where μεθόδοι probably means “inquiries”). Other forms of reference include: τὰ περὶ τῶν ἀποδείξεων ὑπομνήματα (A13: “books on demonstrations”); τὰ ὑπέρ ἀποδείξεως (ὑπομνήματα) (A15, A18c: “books about demonstration”); αἱ ἀποδεικτικαὶ μεθόδοι (A7: “demonstrative methods/inquiries”); or ἡ λογικὴ θεωρία (A23: “the study of reasoning”). Later Greek sources never use the original title, referring to *Dem.* rather as οἱ ἀποδεικτικοὶ λόγοι (B5) or, more commonly, ἡ ἀποδεικτικὴ (πραγματεία) (B2, C4, E1a, F4); the latter description is already found in Galen (A5).

The name περὶ ἀποδείξεως was traditional, or understood as such. Galen uses it as an alternative title of *Posterior analytics*, one that is closer to Aristotle’s own description of the subject matter of that work.<fnref n="109" /> Galen refers to his own περὶ ἀποδείξεως as a place where, as he puts it, he explained “clearly and extensively” the statements that “the ancients” (οἱ παλαιοὶ) made in “the [books] on demonstration” (ἐν τοῖς περὶ ἀποδείξεως) (A25). It is clear from the context (A24) that “the ancients” are Theophrastus and Aristotle (mentioned in this order) and their “books on demonstration” are their respective

<figure><img src="image_11.png" /></figure>

<footnote n="107">107 See esp. A4, A26, D1, D2, G2, G25, and G26.</footnote>

<footnote n="108">108 A16, A18, A18a, A18b, A25, A27, B1, B3, F6, and F9. When referring to a multivolume treatise, Galen typically describes it in the plural, each individual volume being called ὑπόμνημα, βιβλίον, γράμμα, σύγραμμα, λόγος, etc. The singular description of a multivolume treatise is usually πραγματεία. Thus it is somewhat surprising that, on two occasions (A19, C1), Galen refers to *Dem.* by a singular phrase ἐν τῷ περὶ ἀποδείξεως, where the referent is masculine or neuter, presumably λόγος or γράμμα. One would expect that this form would be accompanied by a reference to a specific volume (as in D2, G2, etc).</footnote>

<footnote n="109">109 *PHP* II.3.12 (112,7 De Lacy / V.222 K): ἐν δὲ τοῖς περὶ ἀποδείξεως, ἀ δὴ καὶ δεύτερα ἀναλυτικὰ ἐπιγράγουσι. See also *Diff. puls.* IV.17 (VIII.765 K). For Aristotle, see *Lib. prop.* 14.12 (Boudon-Millot 166,11–15 / 11, XIX.42 K), referring probably to *An. pr.* I.4, 25b26–31. That the names “Prior” and “Posterior” (common in Alexander of Aphrodisias) were not yet established in Galen’s time and place is evidenced by his references to *An. post.* not as ὑστερα (“posterior”), but as δεύτερα (“second”). In his commentary on *Prior analytics*, Alexander uses the phrase περὶ ἀποδείξεως to distinguish the contents of *An. post.* from *An. pr.*, the latter being περὶ συλλογισμοῦ. See Alexander of Aphrodisias, *In An. pr.* I, prooem. (6,14–15 and 32–34 Wallies) *et passim*. Nothing suggests that περὶ ἀποδείξεως was also used as a title. However, in his commentary on *Metaphysics*, he does refer to *An. post.* with the phrase ἐν τοῖς περὶ ἀποδείξεως as if it were a title. See Alexander of Aphrodisias, *In Met.* Γ.3 (266,22 and 268,3 Hayduck). The standard reference to *An. post.* in the later Platonist commentary tradition is τὰ ἀποδεικτικά.</footnote>
*Posterior analytics*. Hence by calling the treatise περὶ ἀποδείξεως, Galen situates it in the same tradition.

## Date

There is no explicit statement in Galen about when he wrote the treatise. But there are several indications pointing to an early period of his career. First of all, it must have been written before the first book of *The therapeutic method (MM)*; and – more importantly – it was almost certainly written prior to the second book of *The doctrines of Hippocrates and Plato (PHP)*. This is not only because the latter two texts refer to *Dem*. – cross-references are not a secure indication of chronology, as they could have been added later by Galen’s own hand –,<fnref n="110" /> but also because they presuppose a general description of the method by which they proceed in tackling particular issues, and there is no doubt that such a description was provided by *Dem*.<fnref n="111" /> Now the first six books of *PHP* were composed during Galen’s first stay in Rome, which lasted from 162 to 166.<fnref n="112" /> (The first six books of *MM* appeared about a decade later.)<fnref n="113" /> So (unless a massive revision of *PHP* II took place in later years) *Dem*. must have been written either in the same period or earlier. But there are reasons to think that it does not belong among the writings composed during Galen’s first stay in Rome. In *His own books* Galen gives a detailed report of his literary output during this time, and it would be strange if he failed to mention a treatise of the size and importance of *Dem*.<fnref n="114" /> Furthermore, as von Müller points out, in *PHP* II–III Galen refers four times to *The correctness of names*, a lost piece consisting of three books; but Galen tells us (A9) that *The correctness of names* belongs among works written after *Dem*.<fnref n="115" /> All in all, it seems – as von Müller concludes and as we are convinced – that *Dem*. was composed before Galen’s first arrival to Rome; but

<footnote n="110">110 There are several instances showing that, while revising his earlier works, Galen added references to treatises written later. See J. Ilberg, “Über die Schriftstellerei des Klaudios Galenos,” *Rheinisches Museum für Philologie, N.F.* 44 (1889), pp. 207–239, here pp. 217–218; P. De Lacy, “Introduction,” in *Galeni De placitis Hippocratis et Platonis I–V* (Berlin: Akademie Verlag 2005 [1977]), pp. 12–60, here pp. 47–48.</footnote>

<footnote n="111">111 See A21, A24, A25, and A26 (for *PHP* II); and A15, A16, A22, and A23 (for *MM* I).</footnote>

<footnote n="112">112 See De Lacy, “Introduction,” pp. 46–47, referring to Ilberg, “Über die Schriftstellerei,” p. 228. For the dates of Galen’s first visit to Rome, see also V. Boudon-Millot, *Galien de Pergame: Un médecin grec à Rome* (Paris: Les Belles Lettres 2012), pp. 101–102 and 121–122.</footnote>

<footnote n="113">113 See Ilberg, “Über die Schriftstellerei,” p. 229; V. Lorusso, “Introduzione,” in: V. Lorusso (ed.), *Galeno: Metodo terapeutico libri I–II* (Roma: Edizioni di Storia e Letteratura 2018), pp. xxi-lxxiii, here p. lxix; Boudon-Millot, *Galien de Pergame*, p. 364.</footnote>

<footnote n="114">114 *Lib. prop.* 1.1–18 (136,25–140,8 Boudon-Millot / 93,19–97,2 von Müller / XIX.11–16 K); I. von Müller, “Über Galens Werk vom wissenschaftlichen Beweis,” *Abhandlungen der königlichen bayerischen Akademie der Wissenschaften, philosophisch-historische Klasse* 20 (1895), pp. 403–478, here p. 412.</footnote>

<footnote n="115">115 Von Müller, “Über Galens Werk,” p. 412. As mentioned above, cross-references are not reliable indicators of chronology; nevertheless, in this case too, they are deeply integrated into the text. In particular,</footnote>
probably not long before he left his post as a doctor for gladiators in Pergamum, held between 157 and 161.<fnref n="116" /> If this is correct he wrote the treatise around the age of thirty.<fnref n="117" />

## Purpose

We learn the most about the purpose and intended audience of *Dem.* from Galen's auto-biographical bibliographies. In *His own books* (A1) Galen mentions *Dem.* in the chapter dealing with "books useful for demonstrations". The chapter starts with an autobiographical sketch where Galen describes his quest for a method "by learning which, when someone else presents a demonstrative argument, we could accurately recognize whether it really is one, or whether, as a counterfeit coin, it resembles the genuine, but is in fact fake. At the same time we would be able to find a solution of everything sought by applying a certain procedure."<fnref n="118" /> Galen claims that none of the famous Stoics and Peripatetics to which he entrusted himself "at that time" (κατ' ἑκεῖνον χρόνον) was able to offer anything useful in that regard.<fnref n="119" /> What saved him from the Pyrrhonean ἀπορία, then, were mathematical disciplines and, in particular, their application in astronomy (prediction of eclipses) and architecture (construction of sun dials and water clocks).<fnref n="120" /> This familiar story, whether or not it resembles anything in Galen's life, is designed pri-

Galen's famous critique of Chrysippus' etymology of ἑγώ seems to draw heavily on this treatise: see esp. *PHP* II.2.7 (104,20–22 De Lacy / V.214 K).

<footnote n="116">116 Von Müller, “Über Galens Werk,” pp. 412–414.</footnote>

<footnote n="117">117 Galen was born in August/September 129; see V. Nutton, “The Chronology of Galen’s Early Career,” *The Classical Quarterly* 23 (1973), pp. 158–171, here pp. 159–161. The traditional dating of *Dem.* has been questioned by J. Jouanna, “Médecine et philosophie: la réception de la science aristotélicienne chez Galien,” in Y. Lehman (ed.), *Aristoteles Romanus: La réception de la science aristotélicienne dans l’Empire gréco-romain* (Turnhout: Brepols 2013), pp. 159–181, here pp. 171–172. Jouanna finds it hard to believe that a treatise to which Galen later attached so much wisdom and importance would have been composed at such a young age. Unfortunately, Jouanna does not engage with (or cite) von Müller’s arguments. The objection based on youth is perhaps not too serious. Galen attended philosophical lectures from the age of fourteen; and, irrespective of the date of *Dem.*, he wrote a number of philosophical works in his twenties, and some even earlier; see *Lib. prop.* 14.16 (167,6–14 Boudon-Millot / 11, XIX.43 K). See below, p. 27. Another potential objection against the early date (not raised by anyone to our knowledge) is our testimonium C15a, Rāzī’s quotation from *Dem.* referring to *De usu partium* (probably book XVII). *UP* (except for the first book) was written early in Galen’s second period in Rome, which started in 169. See Boudon-Millot, *Galien de Pergame*, p. 372. Perhaps some parts of *Dem.* were finished only at that time. But a better explanation is that Galen added the reference as he revised his earlier work; see above, p. 25 n. 110.</footnote>

<footnote n="118">118 *Lib. prop.* 14.2 (164,9–16 *Boudon-Millot* / 11, XIX.39 K).</footnote>

<footnote n="119">119 It is not clear what period of his life Galen has in mind (assuming that his narrative is not simply a literary fiction); he could mean the early years of his philosophical formation, i.e. between the fourteenth and sixteenth years of age. See Boudon-Millot, *Galien de Pergame*, pp. 35–44.</footnote>

<footnote n="120">120 *Lib. prop.* 14.3–5 (164,14–165,7 Boudon-Millot / 11, XIX.39–40 K).</footnote>
marily to introduce the notion of demonstration and to promote the treatise written on this issue. “Therefore,” Galen concludes, “I advise anyone who wants to be trained (ἀσκηθῆναι) in linear demonstrations to be educated in them and then read my treatise *On demonstration*.”<fnref n="121" />

Of course, *Dem.* was neither about astronomy nor architecture and the connection between these disciplines and the agenda of *Dem.* is not explained. Yet it is at least hinted at in the immediately following lines where Galen lists a number of thematically related commentaries he wrote to “exercise himself” (γυμνάζων ἐμαυτόν): three volumes on Aristotle’s *De interpretatione*; eight on *Prior analytics* (four on each book); eleven on *Posterior analytics* (six on the first book and five on the second); six on Theophrastus’ *On affirmation and negation*; and a commentary on Eudemus (of Rhodes)’s *On expression*.<fnref n="122" /> The structure of the chapter suggests that these commentaries were written before *Dem.* For, in the next section Galen goes further back in the past and mentions a commentary on Chrysippus’ syllogistics he composed “while still a child” (ἔτι παῖς ὦν);<fnref n="123" /> and many other essays made by him as a “youngster” (μειράκιον).<fnref n="124" /> Then he turns to works written after *Dem.*<fnref n="125" /> Apparently, then, *Dem.* is the center around which the chapter is organized, first listing works which precede it, and than those which follow it. Now Galen tells us that, when writing his commentaries on Aristotle, Theophrastus, and Eudemus, he exercised himself. When this is read in light of

<footnote n="121">121 *Lib. prop.* 14.8 (165,19–23 Boudon-Millot / 11, XIX.41 K) = A1.</footnote>

<footnote n="122">122 *Lib. prop.* 14.11–14 (166,8–22 Boudon-Millot / 11, XIX.41–42 K).</footnote>

<footnote n="123">123 This was probably after Galen turned fourteen. See *Lib. prop.* 14.16 (167,6–10 Boudon-Millot / 11, XIX.43 K), on writing the commentary when he started attending lectures on Stoic logic; and *Aff. dig.* 8.3 (28,9–11 De Boer / V.41 K), where Galen specifies that he started attending these lectures “having completed the fourteenth year” (ὑποπληρώσας τετταρεσκαιδέκατον ἔτος). See also *Ord. lib. prop.* 4.4 (99,24 Boudon-Millot / XIX.88 K): “...when we were in our fifteenth year” (ἰγνίκα πεντεκαιδέκατον ἔτος ἤγομεν). The word παῖς normally refers to a boy until the age of fourteen; see P. Singer, *Time for the Ancients: Measurement, Theory, Experience* (Berlin: de Gruyter 2022), pp. 46–51, esp. the table on p. 50. This could mean one of three things: (a) until the completion of the thirteenth year (i.e. until one turns fourteen by inclusive reckoning); (b) until the completion of the fourteenth year (i.e. until one turns fourteen by exclusive reckoning); (c) until the completion of the fifteenth year (i.e. including the year when one is fourteen by exclusive reckoning). For inclusive vs. exclusive reckoning of age, see T. G. Parkin, *Old Age in the Roman World* (Baltimore/London: Johns Hopkins University Press 2003), pp. 26–35. Galen apparently uses the word παῖς in the last mentioned sense; see also Boudon-Millot, *Galien de Pergame*, p. 40.</footnote>

<footnote n="124">124 *Lib. prop.* 14.16 (167,6–13 Boudon-Millot / 11, XIX.43 K). It is not clear whether these ὑπομνήματα (which may refer to commentaries, but also to any other texts) include those mentioned earlier or not. The upper age limit of μειράκιον is not certain; in the Hippocratic traditon, it is the third hebdomas, i.e. until twenty-one. But Galen is never specific about this. See Singer, *Time for the Ancients*, pp. 35–66, with the tables on pp. 42 and 50. For the semantic range of ὑπομνήματα see P. van der Eijk, “Galen and the Scientific Treatise: A Case Study of ‘Mixtures’,” in M. Asper and A.-M. Kanthak (eds.), *Writing Science: Medical and Mathematical Authorship in Ancient Greece* (Berlin/Boston: de Gruyter 2013), pp. 145–175, here p. 149.</footnote>

<footnote n="125">125 *Lib. prop.* 14.18–23 (167,14–169,12 Boudon-Millot / 11, XIX.43–45 K) = A9.</footnote>
the story about the quest for method, a picture emerges of a student who approaches
ancient Peripatetic texts about logic with one goal in mind: to find a connecting link
between geometrical proof and philosophy, a link he has been missing in his philosoph-
ical education. By reading and commenting upon these texts, he “exercises himself”
presumably in the sense that he critically engages with them and learns to articulate his
own view with their help. In other words, he rediscover s ancient Peripatetic logic from
the methodological point of view, measuring it by the ideal of geometric proof.

Now Dem. was also conceived as an exercise; but, unlike the commentaries (not
meant for publication, as Galen emphasizes), it was conceived as an exercise for others.
Galen consistently describes the proper way of studying Dem. as training.<fnref n="126" /> As he puts
it in the *Order of his own books*, if a reader not only learns the methods expounded
in Dem. but also trains himself in them, “he will discover the truth in every instance
of the things [under inquiry]” (A4). Thus the methods taught in Dem. are the methods
of discovery, and the purpose of the study is to learn how to apply them to particular
issues.<fnref n="127" /> This is no doubt part of the reason why Galen deals with a number of natu-
ral-philosophical problems in Dem.: they serve as training material, as examples on
which the method, or particular aspects of it, are supposed to be not only understood
but also practised. It does not mean, however, that all these problems must be success-
fully solved – or even solvable. We have already seen that some of these issues, e.g. the
question of the eternity of the world, cannot be solved demonstratively in Galen’s view.
Here is how Abū al-‘Alā’ ibn Zuhr explains the presence of these topics in the treatise
(C11):

For Galen mentions in the treatise *On demonstration* methods of demonstration, using as examples what his predecessors Plato and Aristotle said on topics where a path to perfect certainty has not been found, because it is reasonable to be guided by what they have said. Moreover, since he taught us how demonstrative premisses should be acquired and how to construct syllogisms that draw their conclusion correctly, it is up to him to start from any example that suits him, and it is up to the one who learns this general method to contemplate if this example conforms to the rules or whether it is open to doubt.<fnref n="128" />

<footnote n="126">126 See A4, A6, A7, A13, A27, using the cognates of γυμνάζω. Jaap Mansfeld interestingly suggests that Galen wrote *Dem.* in his youth “to educate himself”, but later came to expect that the treatise “would help the best physicians of the future to educate themselves as well”; see J. Mansfeld, *Prolegomena: Questions to be Settled Before the Study of an Author, or a Text* (Leiden: Brill 1994), p. 126. However, it follows from A27 that Galen conceived of *Dem.* as a training for others from the start.</footnote>

<footnote n="127">127 This is emphasized by R. Chiaradonna, “Le traité de Galien *Sur la démonstration* et sa postérité tardo-antique,” in R. Chiaradonna and F. Trabattoni (eds.), *Physics and Philosophy of Nature in Greek Neoplatonism* (Leiden/Boston: Brill 2009), pp. 43–77; see above, p. 22.</footnote>

<footnote n="128">128 Abū al-‘Alā’ ibn Zuhr, *Solution to the Doubts about Galen*, ed. Koetschet–Rajab (in preparation), fol. 3a, ll. 18–23.</footnote>
Importantly, in accordance with our interpretation, Abū al-‘Alā’ describes these topics as examples (Ar. *mitāl*). Further, he points out that their purpose is not only to demonstrate the successful application of the method, but also to teach the students how to distinguish between cases to which the method can be applied and those to which it cannot. In other words, they serve to develop their independent judgment.

However, Galen’s choice of topics may have been influenced by yet another factor. At least some of them (and the majority of those about which we are informed) belong among the famously controversial issues around which various collections of philosophical δόξα were organized. This is true of the questions of whether the embryo is an animal; in which part of the body the ruling faculty of the soul is; what the substance of the soul is (all probably discussed in books two and three);<fnref n="129" /> whether the world is generated (book four);<fnref n="130" /> issues like time, place, and motion (dealt with in book eight and possibly nine);<fnref n="131" /> the elements and the causes of vision (discussed in book thirteen).<fnref n="132" /> It seems that Galen chose these topics precisely because they were well-known, controversial, and encrusted by batteries of arguments supporting various opinions. This provided him with enough material for a critical assessment of arguments (an important part of the demonstrative expertise, as we have seen); and at least in some cases an opportunity to test the strength of the demonstrative method in resolving these issues.<fnref n="133" /> Individual cases will be discussed in the next chapter.

## Intended audience

In the *Order of his own books* Galen also provides clear indications about his intended audience. This short auto-bibliographic essay is addressed to Eugenianus, a doctor and most probably one of Galen’s students, who is also the addressee of the second part

<footnote n="129">129 Aët. IV.3 (the substance of the soul), IV.5 (the location of the ruling part); V.15 (whether the embryo is an animal).</footnote>

<footnote n="130">130 See Aët. II.4.</footnote>

<footnote n="131">131 See Aët. I.19 (place), I.21–22 (time), I.23 (motion); Sextus, M. X.1–36 (place); 37–168 (motion); time (169–247). However, Galen probably did not deal with motion as such but rather in relation to the question of whether the prime mover is unmoved. In addition, his discussions of these issues seem to be focused exclusively on Aristotle’s *Physics*.</footnote>

<footnote n="132">132 Aët. I.3 (principles and elements); IV.13 (how we see); Sextus, M. X.310–318 (elements).</footnote>

<footnote n="133">133 For Galen’s use of doxographic sources, see T. Tieleman, “Galen and Doxography,” in J. Mansfeld and D. T. Runia (eds.), *Aetiana IV: Papers of the Melbourne Colloquium on Ancient Doxography* (Leiden/Boston: Brill 2018), pp. 453–472, with references to the earlier works by Jaap Mansfeld and Teun Tieleman ibid., pp. 453–454 n. 1. However, the importance of this type of literature for Galen should not be exaggerated; he is primarily dealing with arguments studied first-hand in the original sources, not with textbook opinions. In his choice of topics Galen could have been influenced by a sceptic source (a predecessor of Sextus); see Galen, *Di. dec.* I.5 (IX.794 K); M. Havrda, “The Purpose of Galen’s treatise *On Demonstration*,” *Early Science and Medicine* 20 (2015), pp. 265–287, here p. 279 and n. 62.</footnote>
of *The therapeutic method*.<fnref n="134" /> Galen proposes two starting points for the study of his medical works, one being *On schools (De sectis)*, followed by other texts subtitled “for beginners” (τοῖς εἰσαγομένοις); and the other the lost *On the best school*, followed by *Dem*. The latter route is intended for “those who are both naturally intelligent and disciples of truth” (όσοι καὶ φύσει συνετοὶ καὶ ἀληθείας ἐταῖροι) and who want to become ἀποδεικτικοί, “skilled in demonstration”.<fnref n="135" /> These include specialists in medicine like Eugenianus himself, who are intelligent enough to attain “precise knowledge of things”, rather than relying on correct opinion based on Galen’s reputation.<fnref n="136" /> However, Galen clearly has other readers in mind as well. Whereas *De sectis* is about *medical schools*, the treatise *On the best school* had a more general agenda: its aim was not to praise any particular school of thought, whether medical or philosophical, but “only to indicate what method one might use to construct (@a τις ἂν ... συστήσαιτο) the best school, whether of the medical, philosophical or any other art”.<fnref n="137" /> So the treatise was supposed to be useful not only for doctors, but for specialists in any field, including philosophy. Likewise, it was supposed to provide a general rule for the criticism of any established school of thought: “I have said and shown in that work ... that, whoever wishes to be a fair judge of schools, has to become an expert on demonstration first.”<fnref n="138" /> Here, too, the word “school” (*αἴρεσις*) is not limited to medicine but includes philosophy or any other discipline. This treatise, then, is followed by *Dem.*, whose scope is equally broad:

> One will do well if he wishes to read these books (*sc. On the best school*) first of all; and if, having been persuaded by them, he wants to become skilled in demonstration before embarking on the study of *all the schools* and making a judgement about them, then he has the treatise written by me, the one *On demonstration*.<fnref n="139" />

<footnote n="134">134 For Eugenianus being a doctor, see esp. *Ord. lib. prop.* 3.4 (99,13–14 Boudon-Millot / XIX.88 K); S. P. Mattern, *Galen and the Rhetoric of Healing* (Baltimore: Johns Hopkins University Press 2008), p. 20. See further P. N. Singer, “Galen’s Pathological Soul: Diagnosis and Therapy in Ethical and Medical Texts and Contexts,” in C. Thumiger and P.N. Singer (eds.), *Mental Illness in Ancient Medicine: From Celsius to Paul of Aegina* (Leiden: Brill 2018), pp. 381–420, here p. 414 and n. 56; for Galen’s intended audience more generally, see the bibliography ibid. p. 413 n. 51. For the motif of writing at the request of friends, see J. König, “Conventions of Preparatory Self-Presentation in Galen’s *On the Order of My Own Books*,” in C. Gill, T. Whitmarsh, and J. Wilkins (eds.), *Galen and the World of Knowledge* (Cambridge: Cambridge University Press 2009), pp. 35–58.</footnote>

<footnote n="135">135 *Ord. lib. prop.* 2.1, 2.3 (91,13–15 and 92,4–5 Boudon-Millot / XIX.83 K), and 1.12 (91,1–2 Boudon-Millot / XIX.82 K) = A4.</footnote>

<footnote n="136">136 *Ord. lib. prop.* 3.4 (99,13–18 Boudon-Millot / XIX.88 K) and 2.2–3 (91,15–92,4 Boudon-Millot; XIX.83 K). For the two orders of study, see Mansfeld, *Prolegomena*, pp. 117–126.</footnote>

<footnote n="137">137 *Ord. lib. prop.* 1.6 (89,18–20 Boudon-Millot / XIX.81 K). The word “construction” (*σύστασις*) refers to the way a particular art holds together as a system of thoughts and practices; to “construct” an art then means either to produce an art as a system or, more likely, to understand it as such from its principles; see e.g. Galen, *CAM prooem.* 4–9 (54,14–56,17 *Fortuna* / I.225–227 K).</footnote>

<footnote n="138">138 *Ord. lib. prop.* 1.7 (89,21–90,1 Boudon-Millot / XIX.81 K).</footnote>

<footnote n="139">139 *Ord. lib. prop.* 1.12–2.1 (90,23–91,4 Boudon-Millot / XIX.82 K) = A4.</footnote>
Later on, Galen mentions works that are no longer suitable for medical students but for “those engaged in philosophy” (δόσιοι φιλοσοφία σχολάζουσι).<fnref n="140" /> These works include those dealing with philosophical issues listed in *His own books*.<fnref n="141" /> According to Galen, this purely philosophical part of his œuvre should also be studied after *Dem*.<fnref n="142" /> It follows that he regards *Dem* as an introduction not only to medicine but also to philosophy.

## Genre

According to Galen, then, *Dem.* was an introductory treatise; but it was quite unlike other works he wrote for beginners.<fnref n="143" /> The latter are concise and systematic, providing the reader with a clear and memorable overview of a given topic, usually a summary of the knowledge achieved to date, without polemic or argumentation.<fnref n="144" /> By its length and complexity, *Dem.* rather resembled Galen’s writings for advanced readers (what we might call “scientific treatises”), often consisting of multiple volumes, in which great care is taken to justify every step of the argument, but which also contain his characteristic polemics and digressions.<fnref n="145" /> However, *Dem.* was probably less coherent than, for example, *The therapeutic method, The use of parts, or The power of simple drugs*, since it dealt with a number of disparate issues, whose selection and arrangement seems more or less accidental. Of Galen’s extant writings, *PHP* appears to be the closest to *Dem.* in this respect.<fnref n="146" /> Another feature that the two works must have had in common was the extensive engagement with philosophical material, approached in a largely polemical manner. To use a popular but vague designation, both writings may be described as

<footnote n="140">140 *Ord. lib. prop.* 4.2 (99,15–16 Boudon-Millot / XIX.88 K).</footnote>

<footnote n="141">141 See *Ord. lib. prop.* 4.7 (100,17–20 Boudon-Millot / XIX.89 K), referring to *Lib. prop.*</footnote>

<footnote n="142">142 *Ord. lib. prop.* 4.7 (100,16–17 Boudon-Millot / XIX.89 K).</footnote>

<footnote n="143">143 For the list of works “for beginners” see *Ord. lib. prop.* 2.4 (92,7–3 Boudon-Millot / XIX.84 K). For Galen’s introductory works, see V. Boudon, “Les œuvres de Galien pour les débutants (‘De sectis’, ‘De pulsibus ad tirones’, ‘De ossibus ad tirones’, ‘Ad Glauconem de methodo medendi’ et ‘Ars medica’): médecine et pédagogie au IIe s. ap. J.-C.,” in W. Haase (ed.), *Aufstieg und Niedergang der Römischen Welt II.37.2: Wissenschaften (Medizin und Biologie [Forts.])* (Berlin/New York: de Gruyter 1994), pp. 1421–1467.</footnote>

<footnote n="144">144 See C. Petit, “Galien et le discours de la méthode. Rhétorique(s) médicale(s) à l’époque romaine (Ier–Ile siècle de notre ère),” in J. Coste, D. Jacquart, and J. Pigeaud (eds.), *La rhétorique médicale à travers les siècles : actes du colloque international de Paris, 9 et 10 octobre 2008* (Droz: Paris, 2013), pp. 49–75, here pp. 66–67; eadem, *Galien de Pergame ou la rhétorique de la Providence: Médecine, littérature et pouvoire à Rome* (Leiden: Brill 2018), p. 33. The description does not apply to *De sectis*, except for its brevity, clarity, and simplicity of style, praised already by Photius; see Petit, *Galien de Pergame*, p. 15.</footnote>

<footnote n="145">145 For the style of Galen’s scientific prose see esp. van der Eijk, “Galen and the Scientific Treatise”; Petit, *Galien de Pergame*.</footnote>

<footnote n="146">146 For the order of composition in Galen’s major treatises, see the splendid overview by R. Flemming, “Galen’s Imperial Order of Knowledge,” in J. König and T. Whitmarsh (eds.), *Ordering Knowledge in the Roman Empire* (Cambridge: Cambridge University Press 2007), pp. 241–277; for *PHP* see ibid., pp. 251–252.</footnote>
philosophical miscellanies.<fnref n="147" /> Both were loosely structured discussions dealing with a variety of (mainly philosophical) sources from the perspective of an overarching agenda: in *PHP*, to prove that the most important doctrines of Hippocrates and Plato were in agreement, and to confirm them with scientific argument; in *Dem.*, the agenda was more general, focusing on the universal method of inquiry and proof. Our testimony do in fact indicate that there was significant overlap between *PHP* VII and *Dem*. XIII, and there was also some degree of overlap between *PHP* II and *Dem*. III, and between *PHP* VII and *Dem*. V. Reading these books of *PHP* probably brings us as close to *Dem.* as any Galenic treatise, although certain methodological issues, such as the distinction between four kinds of premisses, were probably discussed at much greater length in *Dem.* than they were in *PHP*.

Another indicator of the genre of *Dem.* is arguably the *Liber logicus* by Clement of Alexandria. The parts selected as B6* and B7* give us precisely what we would expect of an introduction to a philosophical topic, whose aim is not just to present a summary of knowledge, but to bring the reader to an understanding of the subject matter in successive steps. It starts with a distinction between the meaning of the name by which the thing proposed for inquiry is called, the existence of the thing signified, and the substance of that thing, and applies it to the object of the present διδασκαλία, namely, ἀπόδειξις (“demonstration”).<fnref n="148" /> The notion of a proper order (τάξις) is emphasized in this connection, just as it is in other places of Galen’s works where the same successive steps of inquiry or teaching are being described.<fnref n="149" /> The background, of course, is Aristotelian.<fnref n="150" /> The argument is accompanied by illustrative examples.<fnref n="151" /> Its aim is not only to explain how things are, but also to provide guidelines for a particular practice, which is to investigate a problem and find its solution. This is again shown by concrete examples, one of which is discussed in detail in B7*.<fnref n="152" /> At one point the argument imitates a real-life exchange with an opponent. Two types of conversation are considered: a dialogue in the form of questions and answers (κατ’ ἑρώτησίν τε καὶ ἀπόκρισιν) and then, when it fails (because the opponent refuses to cooperate, exposing himself as a sophist), an

<footnote n="147">147 For scientific miscellanism in Galen’s time see J. König, *Greek Literature in the Roman Empire* (London etc.: Bloomsbury 2009), pp. 66–76. Although König includes Galen in the chapter on “Science and Miscellanism”, he does not describe him as a miscellanist himself; however, works like *PHP* arguably have some features in common with this manner of writing. See also König, “Conventions,” pp. 35–40.</footnote>

<footnote n="148">148 Clement of Alexandria, *Lib. log.* (= *Strom.* VIII) 2.3.3–4 and 3.4.3–5.1 (81,17–24 and 82,2–14 Stählin–Havrda) = B6*[2] and [4].</footnote>

<footnote n="149">149 See M. Havrda, *The So-Called Eighth Stromateus by Clement of Alexandria: Early Christian Reception of Greek Scientific Methodology* (Leiden: Brill 2016), p. 151, on *Lib. log.* (= *Strom.* VIII) 2.3.4 (81,23f. Stählin–Havrda).</footnote>

<footnote n="150">150 See Havrda, *The So-Called Eighth Stromateus*, pp. 149–150.</footnote>

<footnote n="151">151 See B6*[4], on the definition of the Sun; B6*[5], on the meaning of ἄνθρωπος.</footnote>

<footnote n="152">152 See Clement of Alexandria, *Lib. log.* (= *Strom.* VIII) 4.9.7–13.8 (85,14–88,16 Stählin–Havrda) = B7*[3–10], on whether the embryo is an animal or not.</footnote>
exposition (κατὰ διέξοδον), which takes into account and preempts reasonable objec-
tions.<fnref n="153" /> Even if these fragments do not come directly from *Dem.*, they are representa-
tive of the type of didactic prose that must have characterized *Dem*.

<footnote n="153">153 *Lib. log.* (= *Strom*. VIII) 4.11.4 (86,27–29 Stählin–Havrda) = B7*+[7]. For parallels see Havrda, *The So-Called Eighth* Stromateus, p. 189, on 86,28f.</footnote>
## 4 Galen's On demonstration: Reconstruction of the contents

New material gathered since von Müller's pioneering study allows us to revisit the question of the thematic structure of *Dem.* and the contents of each book. This chapter summarizes the results of our investigations in the hope that we will be able to replace von Müller's reconstruction of the whole of Galen's work with an updated picture that will last at least until new discoveries lead to further additions, refinements, or corrections. What, then, do we know about the contents of individual books?

The starting-points of the puzzle are, of course, the testimonia that explicitly mention the number of the cited book. The majority of these belong to books IV and XIII, both of which are extensively quoted by Rāzī and Abū al-'Alā' ibn Zuhr.<fnref n="154" /> As for the rest, we have one reference to book I (B1), one to book III (B2), two to book V (D1 and D2), one to book VIII (E1a), two to book IX (E8 and F1), one to book XI (F3), one to book XII (F7), and two to book XIV (G30 and G31). Based on this, a few other pieces can be put into place, some with certainty, others according to a reasoned estimate. The resulting picture according to our current state of knowledge is as follows.

### The first three books

Von Müller describes the first book as written in the tone of a λόγος προτρεπτικός. It was not, he thinks, an exhortation to arts and sciences (as the extant fragment of Galen's *Protrepticus* is), but "an invitation to become acquainted with the rules of scientific thought and to become practised in them".<fnref n="155" /> This corresponds with Galen's note that, in the first book of *Dem.*, he "encouraged (παρεκάλουν) anyone who attempts to give a demonstration of anything (ἔστις ὅτιοῦν ἀποδεικνύειν ἐπιχειρεῖ) to train themselves in this method first" (B1).<fnref n="156" /> This indicates that his targeted audience are people of a rationalist persuasion, rather than, for example, the Empiricists, of whom it could hardly be said that they attempt to give a demonstration of anything.<fnref n="157" /> In the first book, then, Galen encouraged these people to train themselves in methodology. While doing so, he

<figure><img src="image_12.png" /></figure>

<footnote n="154">154 Galen refers to book XIII by number five times: G1, G2, G10, G25, and G26. Rāzī does so once (G3), but then he specifies his citations as coming also from "this book", "further on", etc. As for the fourth book, it is explicitly mentioned by Philoponus (C4), by Rāzī (C9), and by Abū al-'Alā' ibn Zuhr (C3).</footnote>

<footnote n="155">155 I. von Müller, “Über Galens Werk vom wissenschaftlichen Beweis,” *Abhandlungen der königlichen bayerischen Akademie der Wissenschaften, philosophisch-historische Klasse* 20 (1895), pp. 403–478, here p. 417.</footnote>

<footnote n="156">156 *PHP* II.2.3 (102,26–104,2 De Lacy / V.213 K).</footnote>

<footnote n="157">157 See Galen, *SI* 5 (11,1–2 Helmreich / 1,77 K), on the Empiricists: “...they say that there is no demonstration at all (οὐδὲ τὴν ἀρχὴν ἀπόδειξιν εἶναι φασι).”</footnote>
probably complained about those who produce arguments about medical or philosophical issues without being trained in logic, as he often does in his extant works;<fnref n="158" /> and he may have promoted demonstrative methods as a way of resolving disagreements among schools.<fnref n="159" />

The next secure piece of the puzzle comes from the third book of *Dem*. There, as Nemesius tells us (B2), Galen spoke of the mouth of the stomach as the organ of distress (λύπη), and pointed out that the ancients called the mouth of the stomach “the heart” (καρδία), even thought the actual heart is situated higher up.<fnref n="160" /> This passage, as von Müller points out, is paralleled in *PHP* II, where it is part of the discussion about different kinds of premisses used to solve the problem of the location of the ruling part of the soul (τὸ ἡγεμονικόν).<fnref n="161" /> Among arguments proposed by Galen’s opponents (especially the Stoics) in favour of the cardiocentric view, there is one from “the biting pain in distress” ( Ange� tES en taES λύπαις δήξεως), which these opponents “refer” (ἀναφέρουσιν) to the heart. Since, according to Galen, the pain in distress is located at the mouth of the stomach, there are two explanations of this argument: either the biting pain is associated with the heart because the mouth of the stomach is *close* to the heart; or because they mistakenly think that the biting pain is actually felt *in* the heart. The latter mistake could be explained by the use of the word “heart” (καρδία) to refer to the mouth of the stomach, as documented by quotations from Nicander, Thucydides, and Hippocrates.<fnref n="162" /> Two of these sources (Thucydides and Hippocrates) are also mentioned in B2 and in other respects too both passages are very similar.

The parallel in *PHP* II is probably indicative of the original context of B2. Two considerations speak in favour of this. First, *PHP* II is framed by the distinction of four kinds of premisses: scientific, dialectical, rhetorical, and sophistic; while discussing various cardiocentric arguments proposed by the Stoics, Galen uses them as examples of non-scientific (“inappropriate”) premisses. In the introduction to *PHP* II, he makes several references to *Dem.*, mentioning specifically the discussion of non-scientific premisses such as those produced by Chrysippus (A24 and A25, see also A21 and A26). It is quite probable, then, that some of the Stoic arguments dealt with in *PHP* II were already used for the same purpose in *Dem*. Second, the last section of B7* – the material from *Liber logicus* by Clement of Alexandria – abruptly ends after introducing the

<footnote n="158">158 See e.g. *MM* I.4.15 (52,5–10 Lorusso / X.37 K).</footnote>

<footnote n="159">159 See von Müller, “Über Galens Werk,” pp. 418–422, citing useful parallels in this regard. For Galen’s concern about disagreement, see M. Havrda, “The Purpose of Galen’s treatise *On Demonstration*,” *Early Science and Medicine* 20 (2015), pp. 265–287, here pp. 273–275.</footnote>

<footnote n="160">160 Nemesius, *Nat. hom.* 21 (82,5–13 Morani) = B2.</footnote>

<footnote n="161">161 See von Müller, “Über Galens Werk,” pp. 458–459. For the context, see T. Tieleman, *Galen and Chrysippus On the Soul: Argument and Refutation in De placitis, Books II–III* (Leiden/New York/Köln: Brill 1996), pp. 3–129.</footnote>

<footnote n="162">162 *PHP* II.8.4–13 (158,7–160,2 De Lacy / V.275 K).</footnote>
problem “in which part of the body is the ruling faculty of the soul” (B7*[12–13]).<fnref n="163" /> If B7* goes back to *Dem.*, as we believe it does, this note suggests that in *Dem.* the problem of the location of the ruling part of the soul was discussed after the material excerpted in B7*. But if the ἡγεμονικόν problem was discussed in *Dem.*, we can safely assume that the original context of B2 was precisely that discussion.

Once we bring *Liber logicus* into play, the gaps between B1 and B2 begin to close quite easily. Before introducing the ἡγεμονικόν issue, B7* discusses the problem of “whether the embryo is an animal or not”. That Galen dealt with this problem in *Dem.* is confirmed by B3, Galen’s own report in *De usu partium*.<fnref n="164" /> The definition of ‘animal’ proposed in *Dem.* – as reported by Rāzī in B4 – perhaps comes from the same context.<fnref n="165" /> Now B7* enables us to locate this discussion in *Dem.* It must have taken place before the ἡγεμονικόν issue came up. And since (as B2 indicates) the ἡγεμονικόν issue was dealt with in book three, it follows that Clement excerpted B7* either from an earlier part of book three or from book two of *Dem.* Further, in *Liber logicus*, the discussion about the embryo (B7*) is preceded by B6*, an introduction to the teaching of demonstration. Again, if B6* comes from *Dem.*, it was most probably excerpted from one of the first two books of *Dem.* Now, as we know, the first book was, at least partly, an exhortation to the theory and practice of demonstrative methods. Since B6* is the beginning of the exposition of the teaching of demonstration, not an exhortation to it, we conclude that B6* is most probably excerpted from the second book of *Dem.*

In an important part of B7*, there is a classification of problems based on the distinction between the substance (οὐσία) and the attributes (ἔργα, παθῆ, δυνάμεις) of the thing under investigation (τὸ ζητούμενον). Several kinds of problems are distinguished, relative to which part of the thing is known in advance, and which part is being looked for. With some problems we know the substance and are looking for some of its attributes; for instance, in the case of stones, plants, and animals, whose activities we do not know (B7*[2]).<fnref n="166" /> These are examples from pharmacology, which inquires about the activities of certain substances and the causes of these activities. The question in this type of inquiry is not what these substances are, but rather what they do and why.<fnref n="167" /> Another kind of problems are those where we know some of these attributes but do not know, and inquire about, the substances. Here belongs the inquiry about the soul:

<footnote n="163">163 Clement of Alexandria, *Lib. log.* (= *Strom.* VIII) 4.14.4–5.15.1 (88,25–33 Stählin–Havrda).</footnote>

<footnote n="164">164 *UP* XV.5 (357,24–28 Helmkreich / IV.238–239 K).</footnote>

<footnote n="165">165 Rāzī, *Doubts* 13.1 (84,1–13 Koetschet).</footnote>

<footnote n="166">166 Clement of Alexandria, *Lib. log.* (= *Strom.* VIII) 4.9.1–3 (85,1–13 Stählin–Havrda). See the commentary on this passage in M. Havrda, *The So-Called Eighth Stromateus by Clement of Alexandria: Early Christian Reception of Greek Scientific Methodology* (Leiden: Brill 2016), pp. 179–181.</footnote>

<footnote n="167">167 See, e.g., Galen, *SMT* II.5 (XI.474–475 K) and references below, *ad loc.* The problem of the embryo also belongs to this category, for here the question ultimately is whether the thing known as the embryo has certain attributes, namely, the capacity to perceive and move by impulse; see Clement of Alexandria, *Lib. log.* (= *Strom.* VIII) 4.9.8–9 (85,18–21 Stählin–Havrda) = *Dem.* B7*[3].</footnote>
we know its affections, for example, but we do not know what it is (B7*[2]). The question of the bodily location of the ruling part of the soul is introduced as an example of a problem belonging to this class (B7*[12]).<fnref n="168" /> Now Nemesius informs us that Galen mentioned the substance of the soul in *Dem.*, saying “that he would prefer not to assert anything about it” (B5). In light of B7*[12], we can assume that this issue was addressed in the third book of *Dem.*, in connection with the question of the ἡγεμονικόν.

Moving on to somewhat shakier ground, the following observation can be added. As we shall see further on, it is possible that other parts of *Liber logicus* than those listed as B6* and B7* go back to *Dem*. This could be true of two sentences at the very beginning of *Liber logicus*:

ἀλλ' οὐδὲ οἱ παλαίτατοι τῶν φιλοσόφων ἐπὶ τὸ ἀμφισβητεῖν καὶ ἀπορεῖν ἑφέροντο. (...) οἱ μὲν γὰρ νεώτεροι τῶν παρ' Ἕλλησι φιλοσόφων ὑπὸ φιλοτιμίας κενῆς τε καὶ ἀτελοῦς ἐλεγκτικῶς ἄμα καὶ ἑριστικῶς εἰς τὴν ἄχρηστον ἐξάγονται φλυαρίαν.

However, the most ancient philosophers did not indulge in disputing and puzzling over things. (...) For the more recent Greek philosophers, under the sway of vain and ineffectual ambition, are sidetracked into useless verbal quibbling by refutations and contentious arguments. (*Lib. log.* = *Strom.* VIII.1.1.1, 80,3–8 Stählin–Havrda).<fnref n="169" />

The omitted part between these sentences is Clementine and Christian: “So how could we [indulge in these things], we who cling to the really true philosophy and whom Scripture outright commands to seek for the sake of finding, so that we investigate?” But the sentences themselves possibly come from the same source as the excerpts starting with our B6*. The contrast between οἱ παλαίτατοι τῶν φιλοσόφων and οἱ νεώτεροι τῶν φιλοσόφων is not found anywhere else in Clement, but is typical of Galen (even though not limited to him).<fnref n="170" /> In *MM* I.4.15, Galen draws this contrast specifically in connection with the theory of demonstration and the attitude to its principles. First he refers to the views of “ancient philosophers” (οἱ παλαιοὶ φιλόσοφοι) about two kinds of plainly manifest things (τὰ φαινόμενα); this passage, which includes a reference to *Dem.*, is our testimonium A15. Later on, Galen contrasts the ancient philosophers with “certain combative philosophers” (ἔνιοι τῶν φιλόσοφων ἑρίζοντες) who “dispute” (ἀμφισβητοῦσιν) rational principles and argue that “the only thing of which they have firm knowledge is that nothing can be demonstrated” (αὐτὸ γοῦν τοῦτο βεβαίως ἐπίστανται, τὸ μηδὲν ἀποδειχθῆναι δύνασθαι).<fnref n="171" /> It is quite possible that, in these two sentences, Clement preserves a fragment of Galen’s polemic against these deniers of demonstration. This contention is supported by the vocabulary used, in particular the rare (and distinctly

<footnote n="168">168 *Lib. log.* (= *Strom.* VIII) 4.14.4 (88,27–30 Stählin–Havrda).</footnote>

<footnote n="169">169 Havrda’s 2016 translation revised with the help of Robert Bostock.</footnote>

<footnote n="170">170 See Havrda, *The So-Called Eighth Stromateus*, pp. 130–131.</footnote>

<footnote n="171">171 *MM* I.4.15 (52,1–5 Lorusso / X.37 K).</footnote>
Galenic) expression ἄχρηστος φλυαρία.<fnref n="172" /> If so, the fragment would most suitably be placed either in the first book of *Dem.* or somewhere near the beginning of the second.

Putting these pieces together, we arrive at a coherent and relatively detailed picture of the first three books of *Dem.*, which (apart from the beginning) is quite different from the picture drawn by von Müller. The first book was an invitation to the study and practice of rational methods of inquiry and proof, which Galen describes as demonstrative. Mastering these methods qualifies a person as ὁ ἀποδεικτικὸς ἀνήρ (“the man skilled in demonstration”).<fnref n="173" /> A significant aspect of this skill is its universality, i.e., the applicability of the demonstrative methods to “everything capable of being demonstrated” (A12). Details escape us, but similarly motivated passages from other writings of Galen (as well as some unplaced testimonia) allow us to get a rough idea of the content and tone of the first book. It probably raised the issue of the disagreement among schools, and criticized those who attempted to make demonstrations without understanding what it entails.<fnref n="174" /> It probably praised geometrical proofs, and emphasized the importance of training in this area.<fnref n="175" /> It probably included the defence of the very possibility of demonstration, partly based on the authority of “the ancients”, and a preliminary account of the criteria, according to which demonstration is a “technical” criterion of knowledge.<fnref n="176" />

This “exhortatory” part was followed – most likely in the second book – by an introduction to the teaching of demonstration, an abridged version of which is preserved in Clement’s excerpts (B6*). The starting point of this teaching (ἀρχὴ τῆς διδασκαλίας) is the meaning of the word ἀπόδειξις, as understood by all native speakers of Greek. This is accompanied by the question of whether the word does actually have a meaning, or whether it is simply like the word βλίτυρι, a meaningless sound. The question of meaning is closely linked to the question of the existence of the thing signified by the word. The word is used in different contexts (juridical, rhetorical, philosophical) and the way it is used, namely as referring to something real, attests to its meaning, and possibly also to the existence of the thing signified (B6*[1]).

In any case, the text distinguishes three stages of inquiry applied to everything investigated (πᾶν τὸ ζητούμενον): starting with the meaning of the proposed word, the

<footnote n="172">172 Cf. Galen, *Adv. typ. scr.* 1 (VII.476,13 K); *Hipp. Epid. III*, II.4 (82,4 Wenkebach / XVIIa.611 K); the only other instance is found in Cyril of Alexandria. For further details on this and similar expressions, see Havrda, *The So-Called Eighth* Stromateus, p. 131 n. 14. Other elements of the sentence, while not exclusively Galenic, are paralleled in Galen; for ἀμφισβητεῖν καὶ ἀπορεῖν (used in connection with the principles), cf. Galen, *SMT* II.2 (XI.462,15f. K): οὐτως ἂν οὐτ’ ἄπορον οὐτ’ ἀμφισβητούμενον ἦν οὐδέν.</footnote>

<footnote n="173">173 See A1, A4, B6*[14]. For ἀποδεικτικὸς ἀνήρ, see Havrda, *The So-Called Eighth* Stromateus, p. 173 n. 146.</footnote>

<footnote n="174">174 See von Müller, “Über Galens Werk,” pp. 418–422; Havrda, “The Purpose,” pp. 273–275.</footnote>

<footnote n="175">175 See *Lib. prop.* 14.8 (165,19–23 Boudon-Millot / 11, XIX.41 K) = A1; above, pp. 28–29.</footnote>

<footnote n="176">176 See above, for the appeal to the “most ancient philosophers”, which is closely related to the doctrine of the criteria; see A15. For the authority of the ancients, see also A24. For the criteria, see A14 and below, p. 47.</footnote>
researcher proceeds to investigate whether the thing signified by the word exists or not, and finally inquires about the nature (φύσις) or substance (οὐσία) of the thing signified (B6*[2]). The discussion of demonstration loosely follows this model, insofar as it proposes a definition of the meaning of the word ἀπόδειξις agreed by all, and then elaborates this definition in order to grasp more precisely what demonstration is. The definition describes demonstration as "an argument that furnishes credence from something agreed to something disputed" (B6*[4]). The subsequent elaboration focuses on the notion of credence (πίστις) and distinguishes two kinds of credence, one that produces scientific knowledge, and one that produces mere persuasion (B6*[5]). Scientific demonstration of course furnishes the scientific kind of credence. This and other details help narrow the definition down to valid syllogisms based on things evident to perception or the intellect (B6*[8–11]).

After this part, which has no doubt reached us in an abridged form (occasionally glossed by Clement), a more extensive version of B7* must have followed. It is quite possible that this section of Clement's excerpts comes from the same book of *Dem.* as B6*. It introduces the notion of a problem (πρόβλημα) and outlines the method of solving problems by means of two procedures: definition of the thing set forth (τὸ προβληθέν) and the search for appropriate premisses (B7*[1]).<sup>177</sup> Having drafted the above-mentioned classification of problems, the author then puts forward a particular example: whether the embryo is an animal or not (B7*[2–3]). A large part of the discussion is taken up by the task of defining the predicate as “that which is capable of perception and motion by impulse”. This definition having been reached, the problem can be reformulated in such a way as to show what premisses allow us to solve it: simply put, we have to find out if the thing called “embryo” is capable of perceiving and moving by impulse (B7*[3–9]). Grasping the problem in this way is to “recognize” it (γνωρίζειν τὰ προβλήματα) (B7*[3]). At the very end, another problem is enunciated: in which part of the body the ruling faculty of the soul is (B7*[12]). In B7*, this discussion is cut short after one sentence, but in *Dem.* it probably went on.<sup>178</sup>

We have seen (based on B2) that the discussion of the ἡγεμονικόν started or continued into the third book of *Dem.*, perhaps somewhat along the lines of the second book of *PHP*. As in *PHP*, the discussion may have served the purpose of illustrating different sorts of inappropriate premisses, although it need not have been limited to that.<sup>179</sup>

<footnote n="177">177 For definition as the starting point, see A15–A19. For appropriate premisses, see M. Havrda, “Galen on Logic and Scientific Method,” in P. N. Singer and R. M. Rosen (eds.), *The Oxford Handbook of Galen*. Oxford: Oxford University Press 2024, pp. 229–249, here p. 235.</footnote>

<footnote n="178">178 For a detailed commentary on B6* and B7*, see Havrda, *The So-Called Eighth Stromateus*, pp. 145–199.</footnote>

<footnote n="179">179 See A24–A26. The correct argument about the ἡγεμονικόν (summarized in *PHP* VIII.1.22, 484,35–486,2 De Lacy / V.655 K) was quite possibly also presented in *Dem*. Although we have no direct evidence, A25 could be hinting in this direction.</footnote>
Book IV

In his book *On decay*, Galen makes the following reference to *Dem.*:

The [proposition] that every generated [thing] will by all means be corrupted does not involve a scientific or necessary consequence. Rather, as was demonstrated in *On demonstration*, it goes as far as the persuasive, even though nearly everyone who points out that aging happens necessarily to animals uses precisely this reason, claiming that aging is the path to corruption following of necessity to all generated [things].<fnref n="180" />

Testimonia from John Philoponus and Rāzī, further complemented by Abū al-‘Alā’ ibn Zuhr, allow us to locate this discussion in the first half of book four and reconstruct its context.<fnref n="181" /> Galen dealt with the proposition “every generated thing will be corrupted” in connection with an argument about the eternity of the world. The argument has been analysed by Riccardo Chiaradonna and Pauline Koetschet and what follows draws heavily on their work.

The question of the eternity of the world is discussed by Galen's Middle Platonist contemporaries, and it is also one of the “doxographic” commonplaces.<fnref n="182" /> Galen's motivation in picking it up in *Dem*. IV, however, seems to be linked to particular arguments about this issue, specifically Aristotle's arguments in the first book of *De caelo*. According to Philoponus, Galen said that

> the thought of the eternal (ή νόησις τοῦ ἀίδιου) is composite (σύνθετος), because it [i.e., the thought] is ungenerated and incorruptible (ἀγένητος καὶ ἄφθαρτος), and each of the two entails the other. (C4)<fnref n="183" />

The sentence involves a metonymic shift whereby the two objects of thought – “ungenerated” and “incorruptible” – are predicated of the thought itself. But that need not detain us.<fnref n="184" /> The thought is composite because its object, “the eternal” (τό ἀίδιον), is thought of as two mutually entailing things: “ungenerated” (ἀγένητος) and “incorruptible” (ἄφθαρτος). In this passage Galen paraphrases Aristotle’s proposition defended at length in *De caelo* I.12.<fnref n="185" /> One of Aristotle’s objectives in defending this proposition is to

<footnote n="180">180 *De marcore* 2 (VII.671–672 K) = C1.</footnote>

<footnote n="181">181 According to Ḩunayn's report in A2, only the first half of the fourth book was available in Arabic translation; so presumably all passages cited by Rāzī and Abū al-'Alā' ibn Zuhr come from the first half of the book.</footnote>

<footnote n="182">182 For the Middle Platonist context, see R. Chiaradonna, “Galen and Middle Platonists on Dialectic and Knowledge,” in T. Bénatouïl and K. Ierodiakonou (eds.), *Dialectic after Plato and Aristotle* (Cambridge: Cambridge University Press 2019), pp. 320–349, here pp. 332–333; for doxographic accounts, see Aët. II.4 with J. Mansfeld and D. T. Runia, *Aetiana* V.2 (Leiden: Brill 2020), pp. 794–815.</footnote>

<footnote n="183">183 Philoponus, *Aet. mund*. XVII.5 (600,3–5 Rabe).</footnote>

<footnote n="184">184 For metonymic shifts of this kind see Havrda, *The So-Called Eighth Stromateus*, pp. 179 and 234.</footnote>

<footnote n="185">185 See esp. *Cael*. I.12, 282a30–b2; cf. Chiaradonna, “Galen and Middle Platonists,” p. 335.</footnote>
demonstrate the impossibility of there being an incorruptible yet generated thing, such as the world according to Plato's *Timaeus*.<fnref n="186" /> Galen is interested in the mutual entailment of the two concepts: while acknowledging that ungenerated entails incorruptible, he argues that the converse statement – that incorruptible entails ungenerated – requires further differentiation of the meanings of “incorruptible”; he distinguishes two: that which “does not admit the account of corruption at all”; and that which is by nature corruptible but eternally restored.<fnref n="187" /> In the second sense of “incorruptible” (which is Platonic, as Galen proves from the *Timaeus* and the *Statesman*) the proposition does not hold (C4).<fnref n="188" />

Having made this distinction, Galen seems to have turned to the question of whether the world is incorruptible in the sense required by Aristotle's argument, i.e. in the sense of not admitting the account of corruption at all. As the Arabic testimonia show, this part of Galen's discussion was based mainly on *De caelo* I.3.<fnref n="189" /> Galen first mentions Aristotle's arguments based on the circular shape and motion of the spheres and planets, according to which they are ungenerated “because they have no contrary”.<fnref n="190" /> It is not clear how he assessed these arguments. Nonetheless he immediately moves to the argument from preception (διά τῆς αἰσθήσεως) in *Cael*. I.3, 270b13–17, which runs as follows:

> But this result also follows sufficiently enough through perception, at any rate for (one might almost say) merely human conviction. For in all of past time, according to the record people have handed down one to another, nothing appears to have changed either in the whole of the outermost heaven or in the parts proper to it.<fnref n="191" />

Galen's version of the argument, as related in C6, C7, and C8, is more detailed but essentially the same:

> If the cosmos could be corrupted, the [celestial] bodies it contains would not remain in one and the same state, nor would the distances between them, or their sizes, or their movements. The water of the sea that existed before us would also have to disappear. But none of these things have ever

<footnote n="186">186 See *Cael*. I.10, 280a30–31; I.12, 283a4–7.</footnote>

<footnote n="187">187 “Not admitting the account of corruptible at all” means “not being compatible with the notion of corruptible under any circumstance”; in other words: “being incorruptible by definition”. Cf. *Philoponus, Aet. mund.* XVII.3 (598,1–4 Rabe). For the expression “have the λόγος of X”, see *Simplicius, In Phys.* VIII.10 (1331,11–12 Diels), quoting *Philoponus*: τὰ δὲ σύνθετα λόγον ἔχει λύσεως, τὰ δὲ λόγον ἔχοντα λύσεως λόγον ἔχει φθορᾶς. See also *Chiaradonna, Galen and Middle Platonists*,* p. 335.</footnote>

<footnote n="188">188 Cf. *Chiaradonna, Galen and Middle Platonists*, pp. 336–337.</footnote>

<footnote n="189">189 As pointed out by P. Koetschet, “Galien, al-Rāżī, et l’éternité du monde. Les fragments du traité *Sur la démonstration*, IV, dans *Les doutes sur Galien*,” *Arabic Sciences and Philosophy* 25 (2015), pp. 167–198. Abū al-‘Alā’ ibn Zuhr’s precious C6 starts in the middle of a sentence, mentioning Plato and then immediately turning to Aristotle. The content of the missing discussion of Plato can be supplemented from *Philoponus’ report*.</footnote>

<footnote n="190">190 See Aristotle, *Cael*. I.3, 270a13–23.</footnote>

<footnote n="191">191 Trans. C. D. C. Reeve: *Aristotle, De Caelo* (Indianapolis/Cambridge: Hackett 2020), p. 7.</footnote>
departed from their initial state or changed, even though astronomers have been observing them for many thousands of years. It follows, therefore, that the world does not age, and therefore is not subject to corruption.<fnref n="192" />

Now, according to Galen, this argument from astronomical observations supports the view that the world is incorruptible. Rāzī complains that if Galen accepts it, then he must also accept that the world is ungenerated, because he states that what is incorruptible is also ungenerated. But this conflicts with other passages where Galen denies having firm knowledge of whether the world is eternal or generated, and even claims that obtaining such knowledge is impossible. This seems like a blatant inconsistency on Galen's part.<fnref n="193" /> Abū al-'Alā' ibn Zuhr defends Galen against this charge. He points out that Galen does not accept the statement "what is incorruptible is also ungenerated" without qualification, but only after certain "determinations and distinctions".<fnref n="194" /> Here Abū al-'Alā' hints at the distinction between two meanings of "incorruptible" reported by Philoponus. The point is that even if Galen accepts the argument from astronomical observations, he may still be undecided at to what kind of incorruptibility it proves.

In any case, Galen seems to have emphasized that the argument from astronomical observations does not *demonstrate* that the world is ungenerated. As Abū al-'Alā' reports,

> Galen is not satisfied with demonstrations based on such statements because of his rigorous approach to this issue, since every opinion that would result from them is approximate: some [statements] produce something approximating certainty, and this is dialectical credence, and some [produce] something which persuades the soul, and this is rhetorical credence. Demonstration, however, corresponds to neither.<fnref n="195" />

This important testimonium recalls the distinction between four kinds of premisses mentioned above: scientific, dialectical, rhetorical, and sophistic. More specifically, it draws a contrast between demonstration, on the one hand, and arguments based on dialectical or rhetorical premisses on the other. Both the dialectical and rhetorical premisses produce some kind of credence (here the Arabic *taṣḍīq* probably translates the Greek *πίστις*): the dialectical credence is close to certainty, whereas the rhetorical

<footnote n="192">192 Rāzī, *Doubts* 2.1 (8,2–6 Koetschet = C6). For the observations of astronomers, see Aristotle, *Cael*. II.12, 292a8–9. Galen’s version of the argument may have been informed by an intermediate source, but we do not know which. For some parallels see Chiaradonna, “Galen and Middle Platonists,” p. 338 n. 51.</footnote>

<footnote n="193">193 Rāzī, *Doubts* 2.2 (8,7–15 Koetschet = C9, see also C2). For Galen’s agnosticism about this issue, see esp. *Prop. plac.* 2.1–3 (Garofalo-Lami); for other passages, see Mansfeld and Runia, *Aetiana* V.2, p. 808.</footnote>

<footnote n="194">194 Abū al-‘Alā’ ibn Zuhr, *Solution to the Doubts about Galen*, ed. Koetschet-Rajab (in preparation), fol. 3b, ll. 9–13 (= C10), referring to C3.</footnote>

<footnote n="195">195 Abū al-‘Alā’ ibn Zuhr, *Solution to the Doubts about Galen*, ed. Koetschet-Rajab (in preparation), fol. 3b, ll. 13–21 = C13.</footnote>
one is mere persuasion. But demonstration is something else, no doubt because it produces firm knowledge.<fnref n="196" />

Now, according to Abū al-‘Alā’, Galen described the opinion arising based on astronomical observations as “proximate”. This probably means that he regarded this argument as dialectical rather than rhetorical.<fnref n="197" /> In any case, he did not regard it as scientific.<fnref n="198" /> This is confirmed by Galen’s own words, cited at the beginning of this section:

> ... the [proposition] that every generated [thing] will by all means be corrupted does not involve a scientific or necessary consequence. Rather, as was demonstrated in *On demonstration*, it goes as far as the persuasive. (C1)

The word “persuasive” (πιθανόν) is by no means limited to rhetorical premisses. Galen described the dialectical premisses as persuasive too.<fnref n="199" /> To all appearances, then, the argument from astronomical observations is an example of a dialectical argument. The reason why Galen discussed it is not difficult to find. It is for the same reason he discussed the Stoic arguments about the ἡγεμονικόν in *PHP* II and probably also in *Dem*. III. It was for the purpose of training in the demonstrative skill, an essential part of which is the ability to “discover and recognize the differences of premisses” (A26). As Abū al-‘Alā’ puts it:

> Galen mentions in the treatise *On demonstration* methods of demonstration, using as examples what his predecessors Plato and Aristotle said on topics where a path to perfect certainty has not been found, because it is reasonable to be guided by what they have said. Moreover, since he taught us how demonstrative premisses should be acquired and how to construct syllogisms that draw their conclusion correctly, it is up to him to start from any example that suits him, and it is up to

<footnote n="196">196 There is a parallel to this use of πίστις in Clement, *Lib. log.* (= *Strom*. VIII) 3.5.3 (82,16–18 Stählin–Havrda) = B6*[5]: “...demonstration in the proper sense is the one that instils scientific credence (ἐπιστημονικὴν πίστιν) into the souls of students, whereas the other kind produces mere opinion. For the meaning of πίστις in this context see Havrda, *The So-Called Eighth* Stromateus, p. 154 (*ad* 81,30–82,1) and p. 158 (*ad* 82,16–18). See also the contrast drawn in *Lib. log.* 3.7.7 (83,33–84,2 Stählin–Havrda) = B6*[9]: “...there are two kinds of credence (πίστις) and demonstration: one producing mere persuasion in the souls of the auditors and one producing scientific knowledge.”</footnote>

<footnote n="197">197 For the characterization of dialectical premisses as “proximate”, see Galen, *PHP* VIII.1.8 (482,6–7 De Lacy / V.651 K), on arguments discussed in *PHP* II: “...some of them were close, namely those that Aristotle habitually calls ‘dialectical’ (τούς μὲν ἑγγύς αὐτῶν, οὖς διαλεκτικούς ἔθος ἐστὶν Ἀριστοτέλει καλεῖν)”.</footnote>

<footnote n="198">198 This is not to say that astronomical observations do not, according to Galen, prove that the world is incorruptible. But he maintains that they do not yield scientific premisses with respect to the conclusion that the world is ungenerated, which is the point at issue in the present discussion. This is because the axiom on the basis of which we could prove that the world is ungenerated requires a different kind of incorruptibility than that which follows from astronomical observations. We are grateful to Riccardo Chiaradonna for pressing us on this issue.</footnote>

<footnote n="199">199 See esp. Galen, *PHP* VIII.1.8 (482,4–8 De Lacy / V.651 K); T. Tieleman, “Galen’s Notion of Dialectic,” in R. J. Hankinson and M. Havrda (eds.), *Galen’s Epistemology: Experience, Reason, and Method in Ancient Medicine* (Cambridge: Cambridge University Press 2022), pp. 136–155, here p. 145.</footnote>
the one who learns this general method to contemplate if this example conforms to the rules or whether it is open to doubt. (C11)<fnref n="200" />

However, it would be rash to conclude that Galen's interest in dealing with these cosmological issues was merely methodological. Abū al-'Alā' attests that Galen followed Aristotle in making the eternal substance in the celestial sphere – the subject matter of the first book of *De caelo* – an object of his own investigation (C15).<fnref n="201" /> He asked four questions about it: (1) Does it exist? (2) Is it sentient? (3) Is it knowledgeable? (4) Is it skillful?<fnref n="202" /> Surprisingly, Galen suggests that three of these questions (1, 3, and 4) can be explored scientifically, because it is possible to find appropriate premisses for them: in Galen's terminology, appropriate premisses are premisses of a scientific argument. No such argument can be made about the second question, presumably because the celestial sphere is too far away for such an investigation. In contrast, in Galen's view, the existence of the eternal substance can be established. Abū al-'Alā' refers to “the arguments described above”, probably referring to Aristotle's arguments in *De caelo*. As to the third and fourth questions, Galen claims that appropriate premisses can be taken from the study of animals and from astronomy (C15). No doubt the study of animals was supposed to reveal the functional organization of bodily parts (later discussed in detail in *UP*), which Galen seems to have causally attributed to the substance of the highest heavenly sphere, without determining what this substance is.<fnref n="203" /> Sadly, we do not know

<footnote n="200">200 Abū al-‘Alā’ ibn Zuhr, *Solution to the Doubts about Galen*, ed. Koetschet–Rajab (in preparation), fol. 3a, ll. 13–25.</footnote>

<footnote n="201">201 Abū al-‘Alā’ ibn Zuhr, *Solution to the Doubts about Galen*, ed. Koetschet–Rajab (in preparation), fol. 3b, l. 26–fol. 4a, l. 15.</footnote>

<footnote n="202">202 The passage is also discussed below, pp. 75–78.</footnote>

<footnote n="203">203 Rāżī says that Galen referred to Aristotle's *Parts of animals*, *Theophrastus' On plants*, and Galen's own *Use of parts* in connection with the claim that “[the circle of the zodiac] is the cause of the generation of animals, plants, and what is found in them of art and wisdom.” The references are puzzling, because: (a) there is no mention of the circle of the zodiac in Aristotle's *PA*; (b) *UP* was most probably written after *Dem*. On (a): In an earlier publication, Pauline Koetschet suggested that Galen actually meant Aristotle's *Generation of animals*, where similar claims are made or hinted at (see *GA* IV.10, 777b18–778a5); P. Koetschet, *Abū Bakr al-Rāżī: Doutes sur Galien. Introduction, édition et commentaire* (Berlin/Boston: de Gruyter 2019), p. XLII. Independently, the same explanation has been proposed to us by Kosta Gligorijević. However – supposing that Rāżī's Arabic correctly represents Galen's Greek –, it is hard to explain why Galen, who quotes *GA* several times in his treatise *On semen*, citing specific books and mentioning that it consists of five books overall, should refer to a passage from *GA* as coming from *PA*. Possibly the references do not concern the particular claim about the causal role of the zodiacal sphere; their point rather is that these treatises provide sufficient premisses in favour of this conclusion, by demonstrating the skill involved in the construction of animals and plants. On the other hand, it is true that, in *UP* XVII, Galen considers the causal role of heavenly bodies in the formation of animals. On (b): The reference to *UP* could have been added by Galen years after the original composition of *Dem.*, a practice abundantly attested in other cases (see above, p. 25 n. 110).</footnote>
whether he developed these interesting points any further in the fourth book or what its other contents were.

## Book V

All three references to book five come from Galen, *PHP* VII, a book dealing with the causes of vision, which to some extent mirrors the discussion of *Dem*. XIII. Hunayn had not got hold of the fifth book, and so apparently it was never translated into Syriac or Arabic. Whereas in *Dem*. XIII, Galen focused specifically on vision and its causes, in book five he discussed the objects of sight, as well as of other senses. The central question of all three testimonia (D1–3) concerns the capacity of sight to discern the size, shape, and distance of the perceived object. Galen argues that, apart from colour, which is its primary sensible,<fnref n="204" /> sight can also perceive the shape and size of the coloured body; in addition, it perceives its position and distance, in other words, it sees the object where it actually is.<fnref n="205" /> For Galen, these capacities belong to sight alone and do not require the cooperation of any other capacity, such as memory and reason.<fnref n="206" /> This is in conflict with the standard Aristotelian view, according to which size, shape, and distance are common sensibles.<fnref n="207" /> As far as size and shape are concerned, touch can sometimes discern them as well, but it does so accidentally.<fnref n="208" /> For touch, the proper sensibles are, firstly, sharpness and bluntness;<fnref n="209" /> then hotness and coldness; but size and shape, just as motion and number, are *accidental* to touch, as they also require memory and deduction.<fnref n="210" /> As far as distance is concerned, Galen disagrees with some Aristotelians who think that it can also be perceived by hearing and by smell.<fnref n="211" /> The proper sensibles of hearing and smell are sounds and scents, respectively, as neither of these, according to

<footnote n="204">204 See Aristotle, *De an*. II.7, 418a29–b2.</footnote>

<footnote n="205">205 *PHP* VII.5.35–37 and 39–41 (460,11–16 and 22–28 *De Lacy* / V.625–626 K) = D1[3–4] and [6–7].</footnote>

<footnote n="206">206 *PHP* VII.5.34–37 (460,8–16 *De Lacy* / V.625–626 K) = D1[3–4]; for deduction and memory, see also *PHP* VII.6.24 (466,27 *De Lacy* / V.634 K) = D3[4].</footnote>

<footnote n="207">207 For shape and size, see Aristotle, *De an*. III.1, 425a16; distance was probably included among common sensibles by Theophrastus and certainly by Alexander of Aphrodisias; see P. Gregoric, *Aristotle on the Common Sense* (Oxford: Oxford University Press 2007), p. 31 n. 11. According to Aët. IV.8.6, shape is the common sensible of sight and touch; distance is the common sensible of sight and hearing; and size is one of the common sensibles of all senses. For sight and touch, see Themistius, *In De an*. V.1 (82,36–37 Heinze); for sight and hearing, see Alexander of Aphrodisias, *De an*. 50,24–25 Bruns–Sharples. These and other parallels are noted by J. Mansfeld and D. T. Runia, *Aetiana* V.3 (Leiden: Brill 2020), pp. 1556–1557.</footnote>

<footnote n="208">208 *PHP* VII.5.36 (460,13 *De Lacy* / V.626 K) and 6.24 (466,27–28 *De Lacy* / V.634 K) = D1[3] and D3[4].</footnote>

<footnote n="209">209 For Aristotle, sharp and blunt, too, are common sensibles; see *De sensu* 4, 442b2–6.</footnote>

<footnote n="210">210 According to Aristotle, all common sensibles are accidental to the individual senses: see *De an*. II.6, 418a9–11; Gregoric, *Aristotle on the Common Sense*, p. 29.</footnote>

<footnote n="211">211 For hearing, see above, n. 207.</footnote>
Galen, “bring with them an indication of their place of origin”.<fnref n="212" /> Galen must have produced detailed arguments to support these conclusions. Those concerning sight seem to have been based on Euclidean optics and the study of the reflection of the visual ray through mirrors.<fnref n="213" />

We cannot be sure what the context of these discussions was. But it is noteworthy that, in this book, Galen presented his own view about a particular issue, rather than analysing an argument; and that this issue, while essentially physiological, is relevant to the theory of demonstration:

> It was demonstrated in [On demonstration] that the starting points of every demonstration are things evidently manifest to sense perception and intellection. (A16)<fnref n="214" />

> Now ancient philosophers claim that there are two is of manifest things: one kind, also acknowledged by the Empiricists, of those discerned by a particular sensation, such as pale, dark, hard, soft, warm, cold, and the like; and the other undemonstrated kind of things that present themselves immediately to intellection. (A15)<fnref n="215" />

The discussion of the proper sensibles is directly related to the question of the primary objects of perception, and thus also of the principles of demonstration. Galen's examples of principles in A15 are proper objects of touch; likewise, scents, sounds and flavours, if they present themselves to the senses as “plainly manifest” (ἐναργῶς φαινόμενα), will count as principles. Galen's arguments about sight, then, could serve the purpose of delimiting the competence of sight in this regard.<fnref n="216" />

If this was the context in which the question of the proper sensibles was raised, then perhaps the fifth book was where the systematic exposition of the theory of demonstration actually only began. No doubt the basic tenets had already been outlined earlier, probably in the second book, as we have seen. However, it seems that a more detailed exposition of these tenets came only later, after the reader had already been familiarized, on the basis of concrete examples, with the methods of analysing problems and distinguishing between different kinds of premisses. After all, this was the core of the demonstrative practice the reader was supposed to master; and it would make very

<footnote n="212">212 PHP VII.7.5 (470,20–21 De Lacy / V.638 K) = D2[6].</footnote>

<footnote n="213">213 PHP VII.5.40 (460,27–28 De Lacy / V.627 K) = D1[7]. Much of this material is discussed by K. Ierodiazonou, “On Sense Perception: Galen in Dialogue with Plato and the Stoics,” in R. J. Hankinson and M. Havrda (eds.), *Galen’s Epistemology: Experience, Reason, and Method in Ancient Medicine* (Cambridge: Cambridge University Press 2022), pp. 218–231.</footnote>

<footnote n="214">214 MM I.5.1 (54,9–10 Lorusso / X.30 K).</footnote>

<footnote n="215">215 MM I.4.14 (50,9–13 Lorusso / X.36 K).</footnote>

<footnote n="216">216 Cf. von Müller, “Über Galens Werk,” p. 465; R. Chiaradonna, “Le traité de Galien *Sur la démonstration* et sa postérité tardo-antique,” in R. Chiaradonna and F. Trabattoni (eds.), *Physics and Philosophy of Nature in Greek Neoplatonism* (Leiden: Brill 2009), pp. 43–77, here pp. 52–53.</footnote>
good sense from a pedagogical point of view if a more detailed explanation of the theo-
retical aspects of the method came at a later stage.

Nor would it be surprising if one of the first topics addressed by Galen at this stage
was the criteria of the discovery of scientific premisses. Galen distinguishes two kinds
of criteria, natural and artificial. As he explains in his polemic against Favorinus, the
theory of demonstration is an artificial criterion of true and false statements, based on
the natural criteria of our senses and mind.<fnref n="217" /> In *PHP* he refers to *Dem.* for a detailed
exposition of this matter:

So then, I will now show how someone can discover the starting point of the discovery of what is
being sought, recalling the [issues] which I discussed at length both in the treatise *On demonstration* and in certain others. For if we possess no natural criterion, we will not be able to discover
a technical one either. But if we have natural criteria, we could also discover a technical one. So
then, do all we human beings possess some common natural criteria? (...) I declare that you all
have natural criteria and I say this as one reminding you, not teaching it or demonstrating it or as
making an assertion on my own authority. What are they? Those who have eyes in accordance with
nature that see visible objects, those who have ears in accordance with nature that hear audible
objects, a tongue that tastes flavours, nostrils [that smell] scents, and the entire skin [that touches]
the objects of touch; and besides these, mind or thought or whatever one wants to call it, by which
we discern what is entailed and what is incompatible and other things that fall under them, among
which are division, composition, and similarity and dissimilarity...<fnref n="218" />

Considering that these issues were discussed in *Dem.* and that they included sense per-
ception, it seems reasonable to suppose that the place where this discussion properly
began was the fifth book.<fnref n="219" />

<footnote n="217">217 Galen, *Opt. doct.* 4.3–4 (104,6–15 Barigazzi / I.49–50 K). The closest parallel to this passage in ancient literature is found in Clement of Alexandria, *Strom.* VII.16.93.2 (66,3–6 Stählin), where the distinction between natural and artificial criteria (known also to Sextus, *PH* II.15 and *M.* VII.31–32, but not used by him in quite the same way) is drawn along similar lines: ἔστι μὲν οὖν κοινά τινα τῶν ἀνθρώπων κριτήρια καθάπερ τὰ αἰσθητήρια, τὰ δ' ἄλλα τῶν βουληθέντων καὶ ἀσκησάντων τὰ ἀληθῆ, τὰ διὰ νοῦ καὶ λογισμοῦ τεχνικὰ λόγων ἀληθῶν τε καὶ ψευδῶν (“Now, there are certain criteria common to all men, such as the sensory organs, while the other, artificial criteria of true and false arguments, acquired through the intellect and reasoning, are confined to those who have made truth their aim and practice”, trans. F. J. A. Hort and J. B. Mayor, *Clement of Alexandria: Miscellanies Book VII* [London/New York: Macmillan 1902], pp. 163–165, modified). Another passage from the seventh book of *Stromateis*, following shortly after the one just mentioned (*Strom.* VII.16.95.3–8), contains close verbal correspondences with parts of *Liber logicus* included in our collection (B6*[3–4] and [8] and B7*[2]). The passage either draws on *Liber logicus* itself or perhaps directly on its philosophical source. It is tempting to think that *Strom.* VII.16.93.2, where the common and artificial criteria are distinguished, draws on the same source, that is to say, on *Dem.* For a more detailed discussion, see Havrda, *The So-Called Eighth Stromateus*, pp. 68–72.</footnote>

<footnote n="218">218 *PHP* IX.1.10–13 (542,4–19 De Lacy / V.722–723 K) = A14.</footnote>

<footnote n="219">219 As mentioned above, the doctrine of the criteria could have been outlined as early as the first book of *Dem.*; see above, p. 38. See also B6*[8–9], on the first principles of demonstration. But a detailed discussion of this issue seems to have started only in book V.</footnote>
The polemic against Favorinus calls to mind another aspect of Galen's discourse about method that could be associated with the fifth book. In the list of works "that provide a broader treatment of what was discussed in [*On demonstration*]" Galen mentions several treatises dealing with scepticism: *On Clitomachus and his refutations of demonstration; On the best teaching against Favorinus; In defence of Epictetus against Favorinus*; and probably also *On self-refuting arguments*; and *On the controversy regarding the apprehension of things*.<fnref n="220" /> This strongly suggests that Galen dealt with scepticism in *Dem*. too. If he did, then presumably he would have *refuted* the sceptic arguments against the possibility of firm knowledge; and he would have *defended* this possibility, as it is the very foundation of the demonstrative theory. One version of both the refutation and defence is found in the second title on the list – *On the best teaching against Favorinus (Opt. doct.)* –, the only one that has survived. There Galen distinguishes between "the older Academics" (οἱ παλαιότεροι Ἀκαδημαικοί) and the more recent ones like Favorinus. The former assume that the arguments on both sides of an issue lead to "suspension" (ἐποχή), by which they mean "that indeterminacy ... which consists in determining nothing on any matter and asserting nothing firmly" (τὴν ἀοριστίαν ὅπερ ἐστι περὶ μηδενὸς πράγματος ὁρίσασθαι μηδ' ἀποφήνασθαι βεβαίως). The latter "sometimes advance suspension so far that they do not even allow that the sun is apprehensible (καταληπτόν), and sometimes advance judgement so far that they entrust it to their pupils without their first having been taught any criterion of knowledge (ἐπιστημονικὸν κριτήριον)".<fnref n="221" /> Apart from pointing out the inconsistency of Favorinus' position, Galen argues that the best teaching is that which relies on credible starting points, and no starting points are more credible that that which is plainly manifest to perception and intellect.<fnref n="222" /> If the polemic went along similar lines in *Dem.*, it would probably have included the reference to the critera, and so the discussion of perception and its objects would find an appropriate place in that context.

In this connection we may add two speculative but not unfounded remarks. In *Liber logicus*, the section B7* of the present collection is immediately followed by a polemic against the sceptic notion of ἐποχή (“suspension of judgement”) and the associated claim that “nothing is firm” (βέβαιον εἶναι μηδέν). In this polemic, the argument of self-refutation is used, which leads to a doubt about the credibility of the criticized position:

> If suspension of judgement says that nothing is firm, clearly if it starts from itself it will invalidate itself first. Either it concedes that something is true and we should not suspend judgement about everything; or it objects by saying that nothing is true, and it will clearly not speak the truth in the

<footnote n="220">220 *Lib. prop.* 14.19–22 (168,4–19 Boudon-Millot / XIX.44 K) = A9[3–6].</footnote>

<footnote n="221">221 *Opt. doct.* 1.1 (92,5–11 Barigazzi / I.40–41 K). I am using an unpublished translation kindly provided to me by Jonathan Barnes. I make one modification in translating the phrase ἐπιστημονικὸν κριτήριον as “criterion of knowledge” instead of “means of knowledgeable judgement”.</footnote>

<footnote n="222">222 Cf. *Opt. doct.* 4.3 (104,3–6 Barigazzi / I.49 K).</footnote>
*Dem.*, or at least parts of it, was studied in the Alexandrian Neoplatonist school.<fnref n="228" /> Since Galen is quoted at the end of a section dealing with scepticism, where the only other authorities mentioned are Plato and Aristotle (and their quasi-sceptic predecessors), it is possible that a larger part of this section goes back to Galen. The similarity of its style to the antisceptic polemic in *Liber logicus* (which is found in the immediate vicinity of a patently Galenic material) lends support to this view, as well as to the hypothesis that Galen is also the source of this part of Clement's excerpts.<fnref n="229" /> However, as plausible as this may be, all indications are indirect. We do not have sufficiently close and specific parallels in Galen to the arguments used in *Liber logicus* or in Olympiodorus (prior to the actual quotation from Galen).<fnref n="230" /> For this reason, we do not include this material among the testimonia of *Dem*.

## Books VI and VII

When it comes to books six and seven, we are left in complete darkness. ᤄunayn did not have them nor are they mentioned in any Greek source. The following remarks – much like those made at the end of the preceding section – are therefore speculative. If it is true that in book five Galen dealt with perception in the context of a discussion about the criteria, then perhaps he pursued this topic further, moving on to the rational criteria and the methods of inquiry associated with them:

> ...and besides these, mind or thought or whatever one wants to call it, by which we discern what is entailed and what is incompatible and other things that fall under them, among which are division, composition, and similarity and dissimilarity...<fnref n="231" />

That Galen dealt with the rational criteria in *Dem*. is pretty much certain. After all, he says so in the passage just cited. They are among “the issues which I discussed at length both in the treatise *On demonstration* and in certain others” (A14). The things “falling under” these criteria (ἀ καταπέπτωκε τούτοις) include division and composition, and similarity and dissimilarity. As Galen makes clear, these topics are relevant to the process of establishing the principles of demonstration: “In just about all my writ-

<footnote n="228">228 See above, p. 8.</footnote>

<footnote n="229">229 In *The So-Called Eighth* Stromateus, pp. 49–50, I suspended judgement about this question. It is worth noting that both in the Olympiodorus passage and in *Liber logicus*, the sceptics are called οἱ ἐφεκτικοί. See Olympiodorus, *Proleg*. 1 (3,32 Busse) and *Lib. log*. (= *Strom*. VIII) 5.16.3 (90,4 Stählin–Havrda). However, the name is quite common in the second century: see *The So-Called Eighth* Stromateus, pp. 215–216, for some examples.</footnote>

<footnote n="230">230 We can only lament the loss of Galen’s polemic against Clitomachus (which would certainly have included a discussion of ἐποχή) or his treatise *On the controversy regarding the apprehension of things*, which would probably have addressed the notion of ἀκαταληψία.</footnote>

<footnote n="231">231 *PHP* IX.1.13 (542,16–29 De Lacy / V.723–724 K) = A14.</footnote>
ings I have pointed out that the demonstration of every doctrine goes back to the ratio-
nal principles (εἰς τὰς λογικάς ἀρχάς ἀνάγεται παντὸς δόγματος ἡ ἀπόδειξις)."<fnref n="232" /> The
capacity to distinguish the similar and the dissimilar, and the methods of division and
composition seem to play an essential role in that regard. In *PHP*, in accordance with the
agenda of that work, Galen collects passages from Plato and Hippocrates dealing with
these issues. But it is perhaps not too bold to conjecture that he dealt with them directly
in *Dem.*, by way of a systematic exposition.<fnref n="233" /> For the reason mentioned above, the sixth
book would have been an appropriate place for this discussion.

Here again, we are reminded of a potentially relevant chapter in *Liber logicus*. The polemic against ἑποχή in section δ is followed by section ε, introduced by the title: “Procedures and principles of inquiries involve and consist in these matters.”<fnref n="234" /> It includes a discussion of division and definition, presented as methods of inquiry. It has been argued that section ε could go back to Galen, as it contains a number of parallels with his writings.<fnref n="235" /> The evidence is less conclusive than in sections β and γ of *Lib. log.* (i.e., our B6* and B7*), and so it is not included in the present collection. If it goes back to Galen, however, its source could well be the sixth or the seventh book of *Dem*. As we shall see, the eighth book, dealing with Aristotle’s definition of time, was probably part of a larger discussion of definition. It could have been preceded by a systematic elaboration of this topic, such as the one found (in a drastically abbreviated form) in *Liber logicus*.

Books VIII and IX

There is one Greek testimonium mentioning book eight and two Arabic testimonia
mentioning book nine. According to Abū al-‘Alā’ ibn Zuhr, in book nine Galen “very
clearly, beyond any doubt, showed Aristotle’s error”; he did so while dealing with “the
conjunction” of categorical premisses, which seems to indicate that, in his discussion
of “Aristotle’s error”, he focused on the validity of Aristotle’s argument, constructed
as a categorical syllogism.<fnref n="236" /> Unfortunately, we do not know what the argument was

<footnote n="232">232 Cf. *PHP* IX.8.1 (590,12–13 De Lacy / V.782 K); trans. De Lacy, modified.</footnote>

<footnote n="233">233 One of the treatises mentioned in A9 is *On similarity* in three books. *On what is said in many ways* is also relevant.</footnote>

<footnote n="234">234 *Lib. log.* (= *Strom.* VIII) 90,7–8 (Stählin–Havrda): Αἰ τῶν ζητήσεων ἔφοδοι καὶ ἀρχαὶ περὶ ταῦτα καὶ ἐν τοὐτοις εἰσίν.</footnote>

<footnote n="235">235 See *The So-Called Eighth Stromateus*, p. 42 n. 122, for the list of parallels. We may add the use of the word ἐρμηνευτικός in *Lib. log.* (= *Strom.* VIII) 6.19.2 (91,32 Stählin–Havrda), which seems to be characteristically Galenic. See R. Chiaradonna, *Ontology in Early Neoplatonism: Plotinus, Porphyry, Iamblichus* (Berlin/Boston: de Gruyter 2023), pp. 128–129.</footnote>

<footnote n="236">236 Abū al-‘Alā’ ibn Zuhr, *Solution to the Doubts about Galen*, ed. Koetschet–Rajab (in preparation), MS Āstān Quds Rīdawī 13997, fol. 13b, 1. 18–23 = E5.</footnote>
about, but it is likely that, as in the case of the discussion in book four (to which Abū al-‘Alā’ refers in the same passage), it concerned some issue in natural philosophy. We know from other sources that Galen addressed three topics of Aristotle’s *Physics* – time, place, and the unmoved mover – in order to expose the flaws of Aristotle’s reasoning. A precious testimonium from Simplicius allows us to locate the discussion of time in book eight. Apparently, then, the line of attack against Aristotle, focusing on his arguments in the area of natural philosophy, continued in the following book.

## a. Time

In the eighth book of *Dem.*, according to Simplicius, Galen criticized Aristotle's argument in *Physics* IV.11, 218b21–219a11, a passage whose aim was to establish that “time does not exist without motion” (the word “motion”, κίνησις, is used in the sense of “change”, μεταβολή).<fnref n="237" /> Aristotle’s argument is the first step towards the definition of time as “the number of motion according to the prior and the posterior”; it establishes the necessary connection between time and motion/change, without yet determining what the connection is.<fnref n="238" /> The argument is based on the following observation, supported by the story of the sleepers by the tombs of the heroes in Sardinia: “When we do not change in our minds at all, or do not notice that we are changing, we do not think that time has elapsed.” According to Aristotle, “if the non-realization of the existence of time happens to us when we do not distinguish any change, but the soul seems to stay in one indivisible state, and when we perceive and distinguish [change] we say time has elapsed, evidently time is not without motion, i.e., change.”<fnref n="239" />

Galen interprets Aristotle as saying that time does not exist without motion “because we conceive of time while moving” (ἐπειδὴ κινούμενοι νοοῦμεν τὸν χρόνον).<fnref n="240" /> Considering that Aristotle links the non-perception of time with the state of “not changing in our mind” (olinάν ... μηδὲν αὐτοὶ μεταβάλλωμεν τὴν διάνοιαν) and the soul’s apparent

<footnote n="237">237 Simplicius, *In Phys.* IV.11 (708,22–34 Diels) = E1a. For “motion” as change, see Aristotle, *Phys.* IV.11, 218b19–20.</footnote>

<footnote n="238">238 The definition is reached in *Phys.* IV.11, 219b1–2.</footnote>

<footnote n="239">239 Aristotle, *Phys.* IV.11, 218b21–219a1: ... ὅταν γὰρ μηδὲν αὐτοὶ μεταβάλλωμεν τὴν διάνοιαν ἤ λάθωμεν μεταβάλλοντες, οὐ δοκεῖ ἡμῖν γεγονέναι χρόνος, καθάπερ οὐδὲ τοῖς ἐν Σαρδοῖ μυθολογουμένοις καθεύδειν παρὰ τοῖς ἤρωσιν, ὅταν ἐγερθῶσι· συνάπτουσι γὰρ τῷ πρότερον νῦν τὸ ὕστερον νῦν καὶ ἐν ποιοῦσι, ἐξαιροῦντες διὰ τὴν ἀναισθησίαν τὸ μεταξύ. ὥσπερ οὖν εἰ μὴ ἤν ἔτερον τὸ νῦν ἀλλὰ ταὐτὸ καὶ ἐν, οὐκ ἂν ἤν χρόνος, οὕτως καὶ ἐπεὶ λανθάνει ἔτερον ὃν, οὐ δοκεῖ εἶναι τὸ μεταξύ χρόνος. εἰ δὴ τὸ μὴ οἴεσθαι εἶναι χρόνον τότε συμβαίνει ἡμῖν, ὅταν μὴ ὁρίσωμεν μηδεμίαν μεταβολήν, ἀλλ' ἐν ἐνὶ καὶ ἀδιαιρέτω φαίνηται ἡ ψυχὴ μένειν, ὅταν δ' αἰσθώμεθα καὶ ὁρίσωμεν, τότε φαμὲν γεγονέναι χρόνον, φανερὸν ὅτι οὐκ ἔστιν ἂνευ κινήσεως καὶ μεταβολῆς χρόνος. Trans. R. P. Hardie and R. K. Gaye, “Phys- ics,” in J. Barnes (ed.) *The Complete Works of Aristotle* I (Princeton: Princeton University Press 1991), p. 69, modified.</footnote>

<footnote n="240">240 Themistius, *In Phys.* IV.11 (144,24–25 Schenkl) = E1, closely parallelled in E1a.</footnote>
staying “in one indivisible state” (ἐν ἐνὶ καὶ ἀδιαιρέτω φαίνηται ἡ ψυχὴ μένειν), this is not an implausible interpretation – although it is vigorously rejected by Themistius and Simplicius. Galen then refutes the argument by means of a counterexample: “For it is also true of motionless things, like the poles of the cosmos and the centre of the earth, that we conceive of them while moving, and yet they do not involve motion.”<fnref n="241" /> According to Simplicius, the motion Galen has in mind is the motion of thought: “For we do not conceive anything with a thought that does not move.”<fnref n="242" /> Ibn Rušd plausibly interprets this motion as belonging properly to *imaginatio*.<fnref n="243" />

Probably in the same section of *Dem.*, Galen also criticized the above-mentioned definition of time ("the number of motion according to the prior and the posterior") as circular:

> Having given a long list of meanings of the 'before and after', [Galen] says that none of them are well suited to [Aristotole's] definition except the one with respect to time. Therefore, time is the number of motion with respect to time.<fnref n="244" />

So Galen rejected Aristotle's view that "the prior and the posterior is first of all in place" (Phys. IV.11, 219a14-17); instead he seems to have argued that the temporal meaning of these determinations is just as primary as the local one; and he concluded that the temporal meaning is the only one applicable in the definition of time. Did Galen supplement this criticism of Aristotle's definition with any positive alternative? Themistius says that, according to Galen, time "is defined by itself" (ἀφορίζεσθαι δι' αὐτοῦ). Simplicius uses different words expressing the same thought: "Galen says that time is elucidated by itself" (δι' ἑαυτοῦ δηλοῦσθαι).<fnref n="245" /> It is not clear, however, whether this comment represents Galen's view about *time* – namely, that it cannot be defined except by itself – or whether it refers merely to the circularity of Aristotle's definition.<fnref n="246" />

<footnote n="241">241 Themistius, *In Phys.* IV.11 (144,27–29 Schenkl) = E1.</footnote>

<footnote n="242">242 Simplicius, *In Phys.* IV.11 (708,31–32 Diels) = E1a.</footnote>

<footnote n="243">243 Ibn Rušd, *In Arist. Phys. IV*, comm. 97, ed. U. R. Jeck, *Aristoteles contra Augustinum*, pp. 164–165 and 248 = E1b. Ibn Rušd probably hints at Aristotle’s view of φαντασία as motion, see Aristotle, *De an*. III.3, 428b10–429a2.</footnote>

<footnote n="244">244 Themistius, *In Phys.* IV.11 (149,5–7 Schenkl) = E2[1]; Simplicius, *In Phys.* IV.11 (718,13–719,18 Diels) = E2[1].</footnote>

<footnote n="245">245 Themistius, *In Phys.* IV.11 (149,4 Schenkl) = E2[1]; Simplicius, *In Phys.* IV.11 (718,30 Diels) = E2a[1].</footnote>

<footnote n="246">246 In its immediate context, the claim that time is “defined by itself” (Themistius) or “elucidated by itself” (Simplicius) is directly linked to the circularity of Aristotle’s definition; see Chiaradonna, “Le traité,” pp. 55–56 and 61, who correctly interprets the verbs as passive, rather than middle (“reveals itself” *vel sim.*). Whether it also reflects Galen’s view of time, that it cannot be defined except by itself – as Chiaradonna, ibid., pp. 61–62, suggests – is another question. One could argue against this interpretation that Galen presents the circularity of Aristotle’s definition as its weakness, not strength; and there seems to be no parallel in Galen’s writings to the view that any object could be defined by itself. This objection also applies to Havrda, “The Purpose,” p. 286.</footnote>
This picture can be further supplemented on the basis of Arabic sources. An important passage in Yaḥyā ibn ‘Adī (E3) cites Alexander of Aphrodisias as its source for the following report:

Galen held that time is subsistent through itself and has no need for motion in its existence, and he said that Plato was of the same opinion on this topic, that is, that he held that time is a substance, by which he meant duration, and motion merely measures and determines it. So Galen says that motion does not produce time for us, but rather produces only day, month, and year for us. Time, though, is existent in itself, and it is related to [motion] accidentally.<fnref n="247" />

If true, this probably pertains to the same discussion about time as reported by The-
mistius and Simplicius. Unlike them, Yaḥyā attributes to Galen certain positive views
about time as well as a particular interpretation of Plato’s position. Nonetheless, these
views are closely linked to Aristotle’s discussion in *Physics* IV, as they deal with the rela-
tion between time and motion. In our passage the argument concerns specifically the
motion producing “day, month, and year”, i.e., the motion of the heavens.<fnref n="248" /> Aristotle is
depicted as a relativist, who understands time as dependent on motion, whereas Plato
is depicted as the proponent of absolute time, which is independent of motion, being
merely measured by it. It seems that, as in book four, Galen confronted Aristotle’s argu-
ment with Plato’s alternative view. Perhaps he even endorsed Plato’s (alleged) view, as
Yaḥyā suggests, at least for the sake of the argument. However, unlike in book four, the
Platonic source of this interpretation is obscure.<fnref n="249" />

Galen attributes to Plato the view that time is a substance (as opposed to its being merely an accident), and interprets this substance as “duration” (Ar. *mudda*). This is a remarkable term, not only because it later occurs in Newton in a similar connection.<fnref n="250" />

<footnote n="247">247 Yaḥyā ibn ‘Adī, *The Philosophical Treatises* (318,6–319,3 Khalifat), trans. Adamson, in “Galen and al-Rāżī on Time,” in R. Hansberger, M. A. al-Haytham, and C. Burnett (eds.), *Medieval Arabic Thought: Essays in Honour of Fritz Zimmermann* (London: Warburg Institute 2012), pp. 1–14, here p. 5, modified by Koetschet. In the last sentence we follow the emendation proposed by M. Rashed (see below, notes to E3).</footnote>

<footnote n="248">248 The background is possibly Aristotle, *Phys*. IV.14, 223a29–224a2.</footnote>

<footnote n="249">249 Sharples links the interpretation with Galen’s view that, according to Plato, there was an eternal disorderly motion prior to the ordering of the cosmos; see R. W. Sharples, “Alexander of Aphrodisias, *On Time,*” *Phronesis* 27 (1982), pp. 58–81, here p. 74, referring to Galen’s *Plat. Tim.* 4, preserved in Arabic (7,1–7 Kraus/Walzer); the passage is translated by P. Adamson, “Galen and al-Rāżī on Time,” pp. 7–8 (T8). However, the deductive steps between this and the view that time is duration independent of motion are far from obvious. See the discussion in Adamson, *ibid*. Perhaps the background passage is rather Plat. *Tim.* 36e2–5, on the origin of the “endless and rational life” of the world soul “for the whole of time” (*πρὸς τὸν σύμπαντα χρόνον*), which could be interpreted in the sense that there is an eternal time belonging to the soul which precedes the motions of the heavenly spheres. Cf. Simplicius, *In Phys.* (783,18–21 Diels).</footnote>

<footnote n="250">250 I. Newton, *Philosophiae naturalis principia mathematica* (London: Joseph Streater 1686), p. 5, def. VIII, schol. 1. Cf. M. Rashed, “Alexandre d’Aphrodisie et la ‘Magna Quaestio’. Rôle et indépendance des scholies dans la tradition byzantine du corpus aristotélicien.” *Les études classiques* 63 (1995), pp. 295–351, here p. 325. For the background to this view in the scholastic literature of the 16th and 17th centuries, see</footnote>
As Andreas Lammer points out, it also occurs in Alexander's *On time* as part of the definition of time, which is claimed to be in full accordance with Aristotle:

> We shall talk about time according to the opinion of the Philosopher without deviating from him in any respect. So, he maintains that, logically (?) speaking, it [sc. time] is the number of the west-bound motion of the sphere and of what is other than this. Thus, its definition is that it is a duration (*mudda*) which motion numbers.<fnref n="251" />

The original Greek word in this passage and in Galen's interpretation of Plato was probably *παράτασις*.<fnref n="252" /> This, at least, is the word used by Simplicius when answering for Galen to Themistius. According to Simplicius, Galen would say that “the prior and the posterior” in the definition of time are not employed in the local sense, as Themistius believes, but “with respect to the duration of being” (κατὰ τὴν τοῦ εἶναι παράτασιν).<fnref n="253" /> These are of course Simplicius' words, not Galens; but Yahyā's report indicates that Galen already used a word whose Arabic equivalent is *mudda*, and *παράτασις* is as good a candidate as any.<fnref n="254" /> Simplicius' phrase “the duration of being” also occurs in his comment on Aristotle *Phys*. IV.12, 220b32–221a9; the particular passage where the phrase is used probably draws on Alexander.<fnref n="255" /> Once again, this cannot be taken as proof that Alexander used the word *παράτασις* in his discussion of time, but we do have the above-quoted passage from his treatise *On time*, which strongly suggests that he did. If this is correct, the following picture emerges: (1) In his critique of Aristotle, Galen used the word *παράτασις* in reference to the Platonic notion of time. (2) Alexander was acquainted with Galen's critique and his use of the word *παράτασις* in this context.<fnref n="256" /> (3) In his own interpretation of Aristotle, Alexander too employed the word *παράτασις*, possibly in direct response to Galen's critique. (4) Whereas for Galen, however (or at

<footnote>M. Edwards, *Time and the Science of the Soul in Early Modern Philosophy* (Leiden/Boston: Brill 2013), pp. 23–34. For the notion of *mudda* in Arabic philosophy, see below, p. 78.</footnote>

<footnote n="251">251 Alexander of Aphrodisias, *Temp*. 8 (20 Badawī / 93 Théry), trans. A. Lammer, *The Elements of Avicenna's Physics* (Berlin/Boston: de Gruyter 2018), p. 452.</footnote>

<footnote n="252">252 This is suggested by Havrda, “The Purpose,” p. 286 n. 83.</footnote>

<footnote n="253">253 Simplicius, *In Phys*. IV.11 (718,25–719,2 Diels).</footnote>

<footnote n="254">254 Galen uses the word *παράτασις* exclusively in the temporal sense; see Galen, *Hipp. Epid. III* III.76 (Wenkebach 165,21 / XVIIa.745 K); *Hipp. Aph*. V.69 (XVIIb.885,11 K); *Tot. morb. temp.* 1 (73,5 Wille / VII.441 K).</footnote>

<footnote n="255">255 Simplicius, *In Phys*. IV.12 (735,17–28 Diels). In this passage Simplicius interprets Aristotle as saying that time is the measure of motion “with respect to the duration of being” (κατὰ τὴν τοῦ εἶναι παράτασιν). Without attributing it directly to Alexander, he does quote Alexander in the next clause, which is presented as the explanation of this interpretation (735,28–31 Diels). The same interpretation is already developed in an earlier passage (*In Phys*. IV.11, 715,29–716,34 Diels), which is introduced with a laudatory reference to Alexander who “explained almost everything correctly” (715,10 Diels).</footnote>

<footnote n="256">256 This is attested by Yahyā’s report, which claims to go back to Alexander’s response to Galen.</footnote>
least for his “Plato”), time was duration independent of motion, for Alexander, it was the duration of being measured by motion.<fnref n="257" />

Even so, the description of time as “duration” was probably not understood by Galen as a definition in the strict sense, i.e., an account expressing the substance of time. So much, at least, follows from Ibn Bāğğa’s report, which includes a reference to Alexander and thus appears to go back to Alexander’s polemic against Galen as well. According to Ibn Bāğğa, “Galen says that one must content oneself with what people know about [time], and that its substance eludes the mind”.<fnref n="258" /> This statement indicates that Galen was agnostic about the substance of time and, whatever definition of time he adopted, he regarded it as a description of “what people know” about it. “What people know” is probably a reference to the common understanding of the meaning of words expressed in the so-called notional definitions.<fnref n="259" /> Perhaps, then, “duration” was just such a definition in Galen’s view, non-committal as to the nature of the substance whose duration time is.

All the reports discussed so far regarding Galen’s polemic about time either mention Alexander of Aphrodisias as their source or may plausibly be traced back to Alexander – either to his commentary on Aristotle’s *Physics* or another treatise dealing specifically with Galen. Now if Alexander paid so much attention to Galen’s arguments about time, it indicates that he was worried about them and thought it was important to defend Aristotle against Galen’s critique. As such it is reasonable to suppose that Galen was one of the anonymous critics of Aristotle addressed in Alexander’s extant treatise *On time*. Indeed, some of the objections against the view that time is the number of motion, reported by Alexander, are reminiscent of Galen, and could plausibly go back to *Dem*. One of them involves the following thought experiment:

> If we were to think of the sphere standing still, its standing still would be in time; and since its standing still would be in time, its motion would be in time; and if its motion is in time, the number that follows its motion is in time too.<fnref n="260" />

At first glance the argument seems rather weak, as it posits the very thing it aims to prove: that time would continue even if the motion of the heaven stopped moving. If the sphere were to stop moving and still be in time, it argues, then the motion of the sphere

<footnote n="257">257 This paragraph summarizes the argument made in Matyáš Havrda, “Je čas akcident pohybu? K antické kontroverzi nad Aristotelovou Fyzikou,” in O. Navrátilová and V. Němec (eds.), *Pole plné rozmanitých bylin: Sborník k životnímu jubileu Lenky Karfíkové* (Prague: OIKOYMENH 2022), pp. 7–27 (in Czech).</footnote>

<footnote n="258">258 Ibn Bāğğa, *Commentary on Aristotle’s Physics* IV.14 (694,13–15 Lettinck) = E4.</footnote>

<footnote n="259">259 For notional (“ennoematic”) definitions, see Chiaradonna, “Galen and Middle Platonists,” pp. 339–349. See esp. Galen, *Diff. puls*. IV.2 (VIII.704 K); *MM* I.5.3 (56,6–9 Lorusso / X.40 K). For the appeal to the common understanding of words, see also Clement of Alexandria, *Lib. log.* (= *Strom*. VIII) 2.3.3 (81,17–20 Stählin–Havrda) = B6*[2], with Havrda, *The-So Called Eighth Stromateus*, pp. 149–150.</footnote>

<footnote n="260">260 Alexander of Aphrodisias, *Temp*. 5 (20 Badawī), trans. Koetschet = E9*.</footnote>
and the number of this motion would be in time too, and so, if time were the number of motion, time would be in time. Alexander brushes the argument aside, on the basis that, if the heavenly motion stopped moving, time would cease to exist, and that such a supposition is vacuous. However, from a later section of Alexander's response, it appears that the argument takes its starting point from Aristotle himself, namely, from the qualification of his definition, according to which time is not only the number of motion but also of rest (Phys. IV.12, 221b7-23). The opponent seems to have argued something like this: "If time is the number of motion and rest, then the sphere of the heaven would be in time even if it stopped moving. (And so its motion and its number is in time too.) Moreover, if the sphere were in time, even if it stopped moving, then the parts of the cosmos that actually do not move – the axis and the centers of the heavenly circuits – are in time too. (And so time is not posterior to motion)." The second part of this argument is addressed by Alexander in the following passage:

> No-one should think that, when we say that time is the number of rest just as it is of motion, then it is necessary for us to say that the diameter of the whole is at rest and that the centres are at rest, and so that it is necessary for [the whole] to be in time. For we do not claim that whatever does not move is in time, since rest according to us is not [in everything] which merely does [not] move or is not moved; rather, it is [in] that which has the ability according to its nature to move and it is at rest only accidentally. This is what we said there <to remove this uncertainty>. And when we say of the poles and of the centers that they do not move, we do not say that they are at rest; because it is not in their nature to move. So it is not necessary for them to be in time.<fnref n="261" />

Whatever the merit of these objections against Aristotle, they resemble Galen's arguments in four respects: as with the other reports, they focus on the relation between time and motion, arguing that time is not posterior to motion; like E1 and E1a, they involve the notion of the poles/axis and centers of the heavenly circuits (the latter being identical with the center of the earth); like the argument about place (E6, discussed below), they involve a thought experiment; and like other instances in *Dem.*, they argue dialectically, based on the premisses taken from the opponent.<fnref n="262" /> None of this *proves* that Alexander's opponent is Galen, but the material at least is close enough to be appended to section E as "presumed testimonia".

Why did Galen discuss time in the eighth book? We cannot be sure; but a plausible interpretation is that he took Aristotle's argument in *Physics* IV as an example of a (failed) search for a definition. On the one hand, Aristotle's discussion is exemplary, as it starts with the question of the existence of time, continues by exploring what others say about time, and, after identifying an attribute of time that, as Aristotle believes,

<footnote n="261">261 Ibid., p. 23, trans. Koetschet = E11*.</footnote>

<footnote n="262">262 For *Dem.*, see C6, C7, C11-13, G4, and G5 (see below, on book XIII); the discussion of the ἡγεμονικόν in *PHP* II, probably paralleled in *Dem*. III to some extent, is based on the cardiocentric premiss; see B. Morrison, "Logic," in R. J. Hankinson (ed.), *Cambridge Companion to Galen* (Cambridge: Cambridge University Press 2008), pp. 66-115, here pp. 75-83.</footnote>
necessarily belongs to it (namely, change), searches for the middle term grasping time's essence.<fnref n="263" /> On the other hand, it is a failure, in Galen's eyes at least, which makes it even more useful as a didactic example. For asking the question why the argument fails enables the reader to learn better what definition is, how to search for it, and what limits there are to its power and application. For Galen, time appears to be an entity that cannot be properly defined, and perhaps need not be: for practical purposes, it suffices to say “what people know about it”; in other words, to articulate the meaning of the word “time” in everyday use. The limits of definition is a topic frequently addressed by Galen in his extant writings.<fnref n="264" />

## b. Place

As already noted, according to *al-Fihrist*, Alexander wrote a treatise against Galen regarding time and *place*.<fnref n="265" /> It is generally supposed by scholars that the part about place focused on Galen's critique of Aristotle's argument about place in *Physics* IV; that a fragment of this critique is preserved by Themistius and Philoponus (E6 and E6a); and that this fragment comes from *Dem*.<fnref n="266" /> All three suppositions are probably correct, as the fragment just mentioned seems to address Aristotle's argument in *Phys*. IV.4, 211b14–19, and it is cited by the same authors who cite the fragments about time, which are explicitly linked to *Dem*. Moreover, unlike some other topics discussed in *Dem.*, we have no indication that Galen dealt with this issue anywhere else. Where exactly in *Dem.* he did so, however, is more difficult to say. Place (just as time) is mentioned in two Arabic testimonia for book thirteen (G6 and G7), and it is quite possible that the Themistius/Simplicius fragment (E6 and E6a) comes from the same book.<fnref n="267" /> On the other hand, Alexander was probably not interested in Galen's arguments for their own sake, but because they challenged Aristotle's views in the *Physics*. Whereas the Arabic sources do not bear any trace of this anti-Aristotelian edge, the Themistius/Simplicius fragment does. And since Galen discussed Aristotle on time in book eight and other topics of Aris-

<footnote n="263">263 See Aristotle, *Phys*. IV.10, 217b29–11, 219b2. The question about the essence of time (its “nature”), which follows after the investigation of its attributes, is posed in *Phys*. IV.10, 218a31.</footnote>

<footnote n="264">264 See Chiaradonna, “Le traité,” pp. 60–62.</footnote>

<footnote n="265">265 Ibn al-Nadīm, *Kitāb al-Fihrist* 7.1 (253 Flügel).</footnote>

<footnote n="266">266 See von Müller, “Über Galens Werk,” p. 471; Chiaradonna, “Le traité,” p. 45; P. Adamson, “Galen on Void,” in P. Adamson, R. Hansberger, and J. Wilberding (eds.), *Philosophical Themes in Galen* (London: Institute of Classical Studies 2014), pp. 197–211, here p. 207.</footnote>

<footnote n="267">267 See Adamson, “Galen on Void,” who suggests that Rāzī’s G6 belongs to the same argument as the Themistius/Simplicius testimonium (E6/E6a), an argument whose actual subject is not place, but void. Even though Adamson is not explicit about this, it seems to follow from his discussion that Galen’s quotation in E6/E6a comes from the same book as Rāzī’s G6, i.e., *Dem*. XIII; see Adamson ibid., pp. 208–210.</footnote>
totle's natural philosophy in book nine, it is reasonable to conclude that the fragment just mentioned also comes from one of these two books.<fnref n="268" />

The commentators cite the fragment in connection with *Phys*. IV.4, 211b14–19, where Aristotle rejects the notion of place as extension (διάστημα):

> The extension between the extremities is thought to be something, because what is contained and separate may often be changed while the container remains the same (as water may be poured from a vessel) – the assumption being that the extension is something over and above the body displaced. But there is no such extension. One of the bodies which change places and are naturally capable of being in contact with the container falls in – whichever it may chance to be.<fnref n="269" />

In his response Galen sets out to defend the notion of separate extension by means of a though experiment:

> But let us suppose that when water is removed, no other body flows in. There remains, therefore, separate extension in between the surface.<fnref n="270" />

> The point of this argument presumably is not to posit the existence of void.<fnref n="271" /> Rather, it aims to show that extension is conceptually separate from body, whichever body it may be, and thereby, presumably, to defend the notion of place as extension. It is rather similar to the argument from the cessation of the celestial motion, produced by one of Alexander's opponents, the aim of which is to show that time is conceptually separate from motion (E9*). Galen's view of time as duration is in line with these arguments. In neither case does Galen seem to propose a definition in the sense of an account that captures the essence of the thing in question. Rather he seems to defend a particular concept of the thing, which, in his view, corresponds to the meaning of the words "time" and "place" in everyday use.<fnref n="272" />

### c. Prime mover

In a treatise mentioned in *His own books*, Galen discussed Aristotle's argument in *Physics* VII that the first mover is unmoved.<fnref n="273" /> Alexander wrote a refutation of Galen about this issue, and the refutation, containing verbatim quotations from Galen, is

<footnote n="268">268 Chiaradonna, “Le traité,” p. 45, thinks that Galen probably criticized Aristotle’s definition of place in *Dem*. VIII. So already von Müller, “Über Galens Werk,” p. 471.</footnote>

<footnote n="269">269 Trans. R. P. Hardie and R. K. Gaye, “Physics,” p. 56.</footnote>

<footnote n="270">270 Themistius, *In Phys*. IV.4 (114,7–8 Schenkl) = E6[1]; Simplicius, *In Phys*. IV.4 (573,19–21 Diels) = E6a[1].</footnote>

<footnote n="271">271 Against Adamson, “Galen on Void,” p. 207, according to whom Galen’s thought experiment was designed to show that void was conceptually possible.</footnote>

<footnote n="272">272 This reiterates the point made in Havrda, “The Purpose,” pp. 286–287 and n. 84.</footnote>

<footnote n="273">273 *Lib. prop.* 17.1 (171,15 Boudon-Millot / 15, XIX.47 K): εἰς τὸ πρῶτον κινοῦν ἀκίνητον.</footnote>