Quid verbumst? Applying a definition of word to L atin in U niversal D ependencies (2025)

Abstract: Words, more specifically “syntactic words”, are at the centre of a dependency-based approach like Universal Dependencies. Nonetheless, its guidelines do not make explicit how such a word should be defined and identified, and so it happens that different treebanks use different standards to this end. To counter this vagueness, the community has been recently discussing a definition put forward in (Haspelmath, 2023) which is not fully uncontroversial. This contribution is a preliminary case study that tries its hand at concretely applying this definition (except for compounds) to Latin in order to gain more insights about its operability and groundedness. This is helped by the spread of Latin over many treebanks, the presence of good linguistic resources to analyse it, and a linguistic type which is probably not fully considered in (Haspelmath, 2023). On the side, this work shows once more the difficulties of turning theoretical definitions into working directives in the realm of linguistic annotation.

## introduction the notion of (syntactic) word is at the centre of a dependency-grammar approach like that of universal dependencies (ud; de marneffe et al., 2021): foot_0 quoting from the project's guidelines, "dependency relations hold between words [. . . ] the basic units of annotation are syntactic words". how this fundamental unit of morphosyntactic analysis can or needs to be defined, however, is still at the centre of debates and contrasting opinions in the community, and it is not directly confronted by the guidelines. in this sense, as part of the cost action "unidive: universality, diversity and idiosyncrasy in language technology" (savary et al., 2024), foot_1 task 2.1 of the working group 2 (lexicon-corpus interface) has been devoting itself to the harmonisation of the definition of syntactic word across languages, gathering information through surveys and regular meetings, and presenting some results at the 3 rd general meeting in budapest in 2025. the main starting point for this endeavour has been established in a paper by haspelmath (2023), where a clear-cut definition of word is given, based among others on his previous works on this topic (haspelmath, 2017, 2021). the same author admits that his definition might result "unnatural" (haspelmath, 2023, cf. §4.5), as it does not precisely overlap with how words have been traditionally identified by each respective language. in fact, even inside ud and unidive's communities, but not limited to them, some approaches are being brought forth to simply "go beyond" the notion of word, cf. (haspelmath, 2025) or the 1 st proposed shared task on morphosyntactic parsing. the definition of word is a particularly acute issue for latin in ud, as this language counts many treebanks managed by different teams and originating from different annotation standards. this fact, among other things, affects the notion of wordhood in each of these treebanks, so much so that efforts have already taken place in order to deal with latin's morphosyntactic harmonisation (gamba and zeman, 2023b,a). the present paper wants to offer a more in-depth overview about "what is a word" foot_2 for what concerns latin, tapping from the experience of unidive working group 2 task 2.1's survey, and moving along two main lines: on the one hand, sketching, on the basis of ud-treebank-driven empirical observations, what the characteristics of the "latin word" are, and, on the other hand, putting to the test haspelmath's (2023) framework. we believe that such a case study can provide useful insights to its actual operability, both for the harmonisation of latin treebanks and of all treebanks in general. latin has the advantage of presenting a good amount of data in ud, of possessing many valid resources for its linguistic analysis, and also of bearing some typological characteristics which we feel are not fully taken into consideration in (haspelmath, 2023). in this study we only refrain from tackling compounding, as we deem the scope of that phenomenon to be worthy of another entire, dedicated study, which can profit from the definition of "simple" words first. further, despite being centered on latin, this work makes scripts available (see section 3) which can be directly, or with little adjustments, applied to any other ud treebank, in order to replicate most of the results shown here for other languages. in fact, it is our hope that the scope of this paper foot_3 be widened and joined by similar case studies so as to create an as cross-linguistic as possible framing of haspelmath's (2023) definition. ud is a collective endeavour and we contribute to it with the language we know best in its context: latin. section 2 constitutes a brief linguistic profile of latin, while section 3 briefly describes the current situation of latin in ud and the data used in this study; section 4 comments on haspelmath's (2023) definition of word; sections 5 and 6 bring forth the analysis; section 7 makes some final remarks and section 8 concludes. ## latin: the language we supply here a concise linguistic profile of latin in order to make the following discussion easier to follow for those not well acquainted with this language. from the historical point of view, the latin language emerged from the latino-faliscan branch of italic, as spoken by the tribe of latini (latins) in latium, roughly corresponding to the modern-day lazio region of central italy. @xcite as such, it is a typical, as it were, ancient indo-european language showing an extensive fusional morphology in all major word classes (nominals, modi-fiers, verbs). @xcite inflection of nominals (including "nouny" adjectives/determiners, cf. stassen, 2003, §9.1, §15) takes place through suffixes encoding at the same time case, grammatical gender and number, and is traditionally subdivided into five "declensions" for nouns and two "classes" for adjectives according to the similarities between sets of suffixes (concerning a "thematic vowel" or the absence thereof); as discussed in sections 5 and 6, it is quite rare to find a nominal element without any inflectional affixes. verbs (including auxiliaries) also inflect mostly fusionally for aspect, mood, number and person of the subject, tense, and voice, and can also take on nominal forms with their own paradigms (cf. cecchini, 2021 for an overview from the point of view of ud). verbal inflection is traditionally subdivided into four main "conjugations" (again according to the presence or absence of a "thematic vowel"), but aspectual distinctions are often much more complex from a morphological point of view (see e. g. pellegrini, 2023), and this might be a consequence of the whole verbal system shifting from being aspect-based to tensed in preliterate times (cf. again stassen, 2003, §10.2). word derivation is, just like inflection, predominantly suffixal, especially with regard to changes in word classes (e. g. deverbal nouns etc.), while prefixation seems to be restricted to the expression of more "lexical" categories such as aktionsart (cf. haverling, 2000 for the verbal system) and degree. this all correlates well with the original dominant verb-final, more precisely sov, word order of latin, which however seems to already show the signs of a shift towards the later romance svo order in historical times (for example, adpositions are chiefly prepositions; cf. adams, 1976), and can vary noticeably for pragmatic and informationpackaging reasons anyway. for finer-grained details on latin syntax, and much more, we refer to the state-of-the-art, comprehensive, monumental work by pinkster (2015, 2021) 3 latin: the data included in circse). taken together, they reach 1 002 202 syntactic words only in ud (making latin one of the most represented languages therein, coming out 9 th out of more than 150) and 2 833 362 in total. the language in these annotated corpora, despite its extended chronology (from antiquity to the renaissance), is rather homogenous, if not for style and genre, from the morphosyntactic point of view, given how it is mostly oriented towards the classical variety (cf. pinkster, 2015, §1.7 for this periodisation) of the 1st c. bce (clackson and horrocks, 2007, chs. v-vi), or at least it does not diverge too much from it (with the exception perhaps of llct, cf. korkiakangas and passarotti, 2011, §3). their annotation, though, is not always homogeneous, as in some cases it is natively ud, in others the result of conversions from other annotation standards, but has been harmonised over time (see gamba and zeman, 2023b,a); in the case of lasla, the original annotation does not even include syntax. with respect to our case study (sections 5 and 6), we are also interested in the annotation of inflectional classes (ud's morpholexical feature infclass), which is not always present. some technical remarks for the analyses in later sections: whenever an analysis is performed, it is always intended to take place on the subcorpus formed by those resources on which it can fully apply (e. g. excluding lasla if syntax is concerned); all lemmas and forms are normalised (in particular: lowercased, @xmath0, @xmath1; to avoid data sparsity, parts of speech have been reorganised partly following 8 http://dev.syntacticus.org/proiel.html 9 https://www.lasla.uliege.be/cms/c_11821932/ fr/lasla-lasla-dataverse (cecchini, 2024), in particular propn is subsumed under noun, foot_7 num under det, foot_8 adv redistributed according to the parts of speech of their bases; foot_9 ; det, num and pron are considered synsemantic (or "functional", or "grammatical") word classes; by lexeme we mean all forms described by a unique couple of lemma plus part of speech. @xcite all data cited in this work and the python scripts to produce them (for latin, but adaptable to any other ud language) are made available through a sharing platform, @xcite mentioned in what follows as "the repository". some are however shown in appendix a for ease of reference. ## defining the word: mh and ud referring to (haspelmath, 2023) for the complete discussion, we only highlight some main points here. haspelmath's (2023), henceforth mh, and ud's frameworks use transversal, but partly overlapping and correlated categories. mh's definition is based on three morphological objects which represent themselves word types, i. e. free morphs, clitics, and roots, to which compounds are added as "second-order" formations. these objects are themselves based on the more fundamental notion of morph (haspelmath, 2020), and on four combining fundamental properties, which we resume in our contentful bound selective affixes free morph -no no no clitic -yes no no root yes -no - the fact that mh also considers elliptical free forms poses a first serious difficulty for us with respect to their identification in our data: if we assume that any argument of a clause can be "extracted" from it to form an elliptical version thereof, we have to consider all arguments in all sentences, and recursively any subordinated arguments of such arguments, not just whole sentences, as possible free forms. this is problematic to deal with both computationally and definitionally. for this reason, we decide to exclude elliptical constructions and limit our first analysis to free forms appearing as sentences coinciding with explicit simple clauses. technically, we consider any sentence for which the subtree of its root foot_14 does not contain any edge labelled with a clausal relation foot_15 (in other words, we exclude sentences with subordinate clauses of any kind), and where all nodes except the root belong to synsemantic parts of speech, foot_16 thus excluding interjections (intj) as extra-lexical elements, unannotated words (x), and ignoring non-lexical elements (punct, sym). we ignore parataxis, and exclude sentences presenting a co-ordination (relation conj) at the root, to avoid elliptical structures: ellipsis is a pervasive phenomenon in similar constructions, with no clear preference in latin for being left-or right-headed, @xcite and it is unfortunately not (yet) signalled in ud's basic annotation. for the same reason, we exclude sentences presenting an orphan relation, which is the hallmark of ellipsis. we also require the feature verbform with value fin to appear in the clause, @xcite or, to accommodate possible "zero copulas", that there be non-clausal arguments (apart from orphan) or predicate modifiers. @xcite finally, words related by the "headless" relations fixed and flat are considered together as single units. @xcite contrary to mh's definition, and expanding it, we do not require the root to be autosemantic, for reasons discussed later. @xcite out of a total of 60 194 syntactically annotated sentences in our corpus, 50 355 do not present a root co-ordination, and among these we find 1410, the 2.3% of all sentences, distinct (normalised) such free forms, headed by 606 distinct lexemes (for a lexeme/form ratio of 43.0%). figure 1 (above) in appendix a shows the distribution of the latter with respect to their parts of speech. as expected, we see that ud's main autosemantic parts of speech verb (1001 types, 350 lexemes), noun (169, 118) and adj (142, 94) dominate: in fact, their definitions greatly overlap with those of mh's roots, as noted in (haspelmath, 2023, p. 287), even if ud does not make semantic distinctions about the concreteness of their meanings, so that these classes will include more morphs in ud than in mh's scheme. we also cannot draw immediate conclusions about the boundness of these roots themselves: they are surely non-selective, in that they are independent from the actual realisations of their arguments and also from their linear order (at least in latin this being only determined by pragmatic factors, cf. spevak, 2010), but some of them, surely not all (cf. the single forms discussed below), might actually require some arguments to be expressed, e. g. a direct object. such an investigation is beyond the scope of this paper, and here we can just note down that boundness emerges as an orthogonal property to ud's parts of speech verb, noun, adj and adv. there is a quantitative gap between these and synsemantic parts of speech, which can be partly explained with the more closed nature of the latter. the exiguity of adv, besides their strong relational and metapredicative nature, @xcite and of aux, not expected to head a predicate by definition, 26 can @xcite though the impact of this is extremely limited in our data. @xcite the results are presented in the repository as the file freeforms.tsv. an even greater divide beckons in the synsemantic field between pron, det and aux, and the other parts of speech not appearing in even one of our free forms: 27 adp, cconj, part and sconj. this is also to be expected, because, beyond being synsemantic, these parts of speech are more or less explicitly defined as connectors, as exclusively grammatical elements introducing nominal or clausal arguments, or conveying morphological or pragmatic features (part), so that it is not easy to imagine them as predicate heads. under this light, we can consider the elements of these classes to be bound to the heads of the phrases they accompany, and so, passing to mh's framework, they are the prime candidates for clitics. in the latin system, these words are also set apart from all others by a lack of inflectional affixes, that is, they are unique forms in their paradigms, even if this does not necessarily mean that they are bare morphs (see section 6). but there is an even more striking characteristic that strengthens their identification with clitics: phonologically, many such words present endings which are not shared, or only marginally, by autosemantic classes, remarking their prosodic boundness. it is the case of adp sub 'under', cconj sed 'but', part non 'not' (cser, 2020, §2). the interesting consequence is that latin seems to have morphologically codified the distinction between roots and clitics, with intermediate degrees for nonclitic synsemantic elements (see section 5.1): the question then arises how common this is typologically. in any case, the identification of roots (if we loosen the request for a concrete meaning) with verb, noun, adj and possibly, partly adv (intended stricto sensu "true", contentful adverbs such as saepe 'often' or uix 'with difficulty', and possibly relators like supra 'above') on one side, and of clitics with adp, cconj, part and sconj on the other side plausibly looks to be universal. ## a good definition (for latin)? trying to identify the morphological objects of mh's definition (see the most immediate issue is that distinguishing a specific type of word for free morphs, as opposed to roots or clitics possibly appearing with affixes, is totally irrelevant for latin, and actually for any language like latin, that is, a language which tends to positively mark through inflectional morphology every term "denoting an action, an object or a property", independently from its semantic complexity (so, be it autosemantic or synsemantic), and where a good part of the lexicon, even uninflectable items, shows transparent extensive derivational processes. only a fragmentary part of latin forms can be identified as free morphs, but this does not really bring any insight into the nature of the latin word. in fact, we get the impression that the inclusion of free morphs in mh's definition might be motivated, on the one hand, by the need to give a place to non completely lexical, difficult to tackle elements such as interjections, and, on the other hand, might be driven by the apparent focus on languages with different, if any, inflectional paradigms than latin. in particular, we would like to stress the fundamental difference that incurs between a language which always marks some kind of grammatical category such as case, number, and/or gender on the members of entire word classes, as is latin, and other languages which only mark them in some circumstances and then possibly "additively", as it seems to be the case for english. even if we are not considering it in this study, we notice that mh's definition of compound will be directly affected by this parameter: if the members of some word class always occur with required affixes, we cannot expect them not to have some affix even when combining with other non-affixal morphs, and this is the case in latin with the so-called linking vowel -i-(see e. g. oniga, 1992; brucale, 2012), so that we have to treat all such cases as instances of multiple, and not single, words. conversely, we cannot expect such a thing as a linking vowel in languages with no required affixes, and so there we will treat most, if not all, morph combinations as single-word compounds. this, in our opinion, will then create an asymmetry in how and how many compounds are identified as single or multiple words in each language, which is ultimately based on a bias with respect to their respective inflectional types; this in turn, in our opinion, seems to run counter to the establishment of a definition which should apply universally with the same criteria, and which instead would take double standards, as it were. so we argue that it is not so much about deciding to always split forms or always lump them together, but that two cases like latin agricultor 'farmer', from ager 'field' and cultor 'tender' with linking -i-, and flowerpot, cited in (haspelmath, 2023), should both be treated as either one single word or two words, but not as two words the former (latin) and one word the latter (english), as would now be the consequence of a direct implementation of mh's definition. another major issue is that, while the distinction between roots and clitics is partly retraceable in ud's part-of-speech system, so morphosyntactically grounded, and partly reflected in phonological and morphological features, it still seems to not be really related to the presence or absence or affixes (for example, if we admit that aux is clitic, then clitics can be inflected; also, some grammaticalised forms transparently bear derivational affixes), or to the status of boundness. in mh's scheme, what is common to all three basic word types is non-selectivity, and this seems to be more relevant: words could then be tentatively defined as nuclei of morphs and affixes which do not always syntactically combine with elements of the same kind. however, on the one hand both boundness and selectivity are not made explicitly relative to linear order or syntactic dependencies in mh's definition; and on the other hand, if we suppose the latter criterion, we can find counterexamples. for example, leaving further detailed investigation about this aspect to future work, we notice that a class such as adp, clitic almost by definition, at least in latin, always selects a nominal head to depend on, meaning a noun proper, a verbal form acting as a nominal (@xmath2, such as an infinitive (cf. cecchini, 2021), or a modifier, which in latin follows nominal morphology. in this sense an adp is selective, but we cannot reasonably treat it as an affix, and this because it is not necessarily adjacent to the nominal in question, while conversely aux is a much stronger candidate for being an affix given its tendency to stay close to its head. unfortunately, the semantic criterion discriminating roots form other morphs does not come to help here in pinpointing what makes all these elements words, as has been observed in section 5.1, and should probably be one of the first criteria to be discarded. ## conclusion the conclusion of this preliminary study, at least for what concerns latin, is that, unfortunately, mh's definition of word is less clear-cut than at first glance when it comes to putting it into practice, and it makes distinctions which do not appear relevant for the latin system, and we dare to say also for typologically similar languages under the inflectional aspect, as could be ancient greek, russian, and others. @xcite in our opinion, some criteria of analysis, such as contentfulness, are already captured by ud's system in an even more systematical approach, and they are anyway (partially) orthogonal to the morphosyntactic ones that we deem have to be at the core of any definition of word, and that are also used in mh's definition. we see a trace, though, that deserves being pursued, and that is just based on selectivity and rigidity of linear order: words, especially in a morphosyntactic context as ud's formalism, can then be those blocks, with a meaningful nucleus and a possible contour of affixes, which can be moved around or separated by other similar blocks inside any possible free form. in this way, a multipartite classification into morphological objects as shown in