# Arabic Thought and Its Place in History/Chapter VI

​ The Aristotelian philosophy was first made known to the Muslim world through the medium of Syriac translations and commentaries, and the particular commentaries used amongst the Syrians never ceased to control the direction of Arabic thought. From the time of al-Ma'mun the text of Aristotle began to be better known, as translations were made directly from the Greek, and this resulted in a more accurate appreciation of his teaching, although still largely controlled by the suggestions of the commentaries circulated amongst the Syrians. The Arabic writers give the name of failasuf (plur. falasifa), a transliteration of the Greek φιλόσοφος, to those who based their study directly on the Greek text, either as translators or as students of philosophy, or as the pupils of those who used the Greek text. The word is used to denote a particular series of Arabic scholars who arose in the third century A.H. and came to an end in the seventh century, and who had their origin in the more accurate study of Aristotle based on an examination of the Greek text and the Greek commentators whose work was circulated in Syria, and is employed as though these falasifa formed a ​particular sect or school of thought. Other philosophical students were termed hakim or nazir.
The line of these falasifa forms the most important group in the history of Islamic culture. It was they who were largely responsible for awakening Aristotelian studies in Latin Christendom, and it was they who developed the Aristotelian tradition which Islam had received from the Syriac community, correcting and revising its contents by a direct study of the Greek text and working out their conclusions on lines indicated by the neo-Platonic commentators.
The first of the series is Yaqub b. Ishaq al-Kindi (d. circ. 260 A.H. = 873 A.D.), who began very much as a Mu'tazilite interested in the theological problems discussed by the members of that school of thought, but desirous of testing and examining these more accurately, made use of the translations taken directly from the Greek and then only recently published. By this means he brought a much stricter method to bear, and thus opened the way to an Aristotelian scholarship much in advance of anything which had been contemplated so far. As a result his pupils and those who came after them raised new questions and ceased to confine themselves to Mu'tazilite problems, and al-Kindi was their intellectual ancestor in those new enquiries which his methods and his use of the Greek text alone made possible. It is a strange fact that al-Kindi, the parent of Arabic philosophy, was himself one of the very few leaders of Arabic thought who was a true ​Arab by race. For the most part the scientists and philosophers of the Muslim world were of Persian, Turkish, or Berber blood, but al-Kindi was descended from the Yemenite kings of Kinda (cf. genealogy quoted from the Tarikh al-Hakama cited in note (22) of De Slane's trans. of Ibn Kkallikan, vol. i. p. 355). Very little is known about his life, save that his father was governor of Kufa, that he himself studied at Baghdad, under what teachers is not known, and stood high in favour with the Khalif Mu'tasim (A.H. 218–227). His real training and equipment lay in a knowledge of Greek, which he used in preparing translations of Aristotle's Metaphysics, Ptolemy's Geography, and a revised edition of the Arabic version of Euclid. Besides this he made Arabic abridgments of Aristotle's Poetica and Hermeneutica, and Porphyry's Isagoge, and wrote commentaries on Aristotle's Analytica Posteriora, Sophistica Elenchi, the Categories, the apocryphal Apology; on Ptolemy's Almagesta and Euclid's Elements, and original treatises, of which the essay "On the Intellect" and another "On the five essences" are the most noteworthy (Latin tr. by A. Nagy in Baeumker and Hertling's Beitrage zur Geschichte der philosophie des MA. II. 5. Munster, 1897).
He accepted as genuine the Theology of Aristotle which had been put into circulation by Naymah of Emessa, and, we are told, revised the Arabic translation. The Theology was an abridgment of the ​last three books of Plotinus' Enneads, and presumably al-Kindi compared this with the text of the Enneads, corrected the terminology and general sense in accordance with the original, and evidently did so without any suspicion that it was not a genuine work of Aristotle. The Theology had not been long introduced to the Muslim world, and it is certain that the use of it made by al-Kindi was a main cause of its subsequent importance. Endorsed by him it not only took an assured place in the Aristotelian canon, but became the very kernel of the teaching developed by the whole series of falasifa, emphasizing the tendencies already marked in the commentary of Alexander of Aphrodisias. The influence of the Theology and of Alexander appear most clearly in the treatise "On the Intellect" which is based on the doctrine of the faculties of the soul as described in Aristotle's de anima II. ii. Al-Kindi, developing the doctrine as presented by the neo-Platonic commentators, describes the faculties or degrees of intelligence in the soul as four, of which three are actually and necessarily in the human soul, but one enters from outside and is independent of the soul. Of the three former one is latent or potential, as the knowledge of the art of writing is latent in the mind of one who has learned to write; the second is active, as when the scribe evokes from the latent state this knowledge of writing which he desires to put into practice; the third is the degree of intelligence actually involved in the operation of writing, where ​the knowledge now quickened into activity guides and directs the act. The external faculty is the "Agent Intellect" ('aql fa''al) which proceeds from God by way of emanation and which, though acting on the faculties in the body, is independent of the body, as its knowledge is not based upon perceptions obtained through the senses.
It is futile to maintain that the history of Arabic philosophy shows a lack of originality in the Semitic mind; for one thing not one of the philosophers of first rank after al-Kindi was of Arab birth, very few could be described as Semitic. It would be more correct to say that the Greek philosophers stood alone, until quite modern times, in attempting anything which could be described as a scientific psychology. Until the methods and material of modern natural science came to be applied to psychological research there was little, if any, advance on the psychological theories of the ancient Greek investigators, and the only point of difference in later schools was as to which particular aspect af ancient research would be selected as the starting-place. Here lies the great importance of al-Kindi, for it was he who selected and indicated the starting-point which all the later Arabic philosophers began from, and selected the material which they developed. The particular basis thus selected by al-Kindi was the psychology of Aristotle's de Anima as expounded by Alexander of Aphrodisias. This was suggested but not in all respects clearly indicated by the Syriac philosophers, ​and it seems certain that al-Kindi's development was very largely influenced by the Theology of Aristotle, a work which he evidently esteemed very greatly. The relation between Alexander Aphr. and Plotinus, whose teaching appeared in the Theology, may be described as being that Alexander's teaching contained all the germs of neo-Platonism, whilst Plotinus shows the neo-Platonic system fully worked out. As first presented this system must have seemed fully consistent with the teaching of the Qur'an, indeed it would appear as complementary to it. In man was an animal soul which he shared with the lower creation, but added to it was a rational soul or spirit which proceeded directly from God and was immortal because it was not dependent on the body. The possible conclusions which proved to be inconsistent with the teachings of revelation were not as yet fully worked out.
We need not linger over al-Kindi's logical teaching which carried on and corrected Arabic study of the Aristotelian logic. This was not a mere side issue, it is true, although logic did not play so important a part in Arabic education as it did in Syriac. In Syriac it was the basis of all that we should regard as the humanities, but in Arabic this position was taken by the study of grammar, which was developed on rather fresh and independent lines, though slightly modified by the study of logic in later times. Still, so long as the Muslim world had any claim to be regarded as fostering philosophical studies, and to ​a less degree even in later times, the Aristotelian logic has been only second to grammar as the basis of a humane education. Al-Kindi's real influence is shown in the introduction of the problems of psychology and of metaphysics, and the work of the falasifa centres in these two studies on the lines indicated by al-Kindi.
In psychology, as we have seen, al-Kindi introduced a system already fully developed by Alexander and the neo-Platonic commentators on Aristotle, kept alive amongst the Syriac students of philosophy, and then further developed from this point by his successors. In metaphysics the circumstances were different. Al-Kindi apparently was the one who introduced the problems of metaphysics to the Muslim world, but it is obvious that he did not clearly understand Aristotle's treatment of these problems. The problems involved in the ideas of movement, time, and place are treated by Aristotle in books iv., v. and vii. of the Physics, which had been translated by al-Kindi's contemporary, Hunayn b. Ishaq, and in the Metaphysics, of which at the time no Arabic translation existed, so that, so far as it was used, al-Kindi must have consulted the Greek text.
The essay "On the Five Essences" treats the ideas of the five conditions of matter, form, movement, time, and place. Of these he defines (a) matter as that which receives the other essences but cannot itself be received as an attribute, and so if the matter is taken away the other four essences are necessarily ​removed also. (b) Form is of two kinds, that which is the essential of the genius, being inseparable from the matter, and that which serves to describe the thing itself, i.e., the ten Aristotelian, categories—substance, quantity, quality, relation, place, time, situation, condition, action, and passion; and this form is the faculty whereby a thing (shay') is produced from formless matter, as fire is produced from the coincidence of dryness and heat, the matter being the dryness and heat, the form being the fire; without form the matter is abstract but real, becoming a thing when it takes form. As De Vaux points out (Avicenne, p. 85) this illustration shows that al-Kindi does not grasp Aristotle's meaning correctly. (c) Movement is of six kinds: two are variations in substance, as either generation or corruption, i.e., production or destruction; two are variations in quantity by increase or decrease; one is variation in quality, and one is change of position. (d) Time is itself akin to movement, but proceeds always and only in one direction; it is not movement, though akin, for movement shows diversities of direction. Time is known only in relation to a "before" or "after," like movement in a straight line and at a uniform rate, and so can only be expressed as a series of continuous numbers. (e) Place is by some supposed to be a body, but this is refuted by Aristotle: it is rather the surface which surrounds the body. When the body is taken away the place does not cease to exist, for the vacant space is instantly filled ​by some other body, air, water, etc., which has the same surrounding surface. Admittedly al-Kindi shows a crude treatment of these ideas, but he was the first to direct Arabic thought in this direction, and from these arose a new attitude towards the revealed doctrine of creation on the part of those who came after him.
Al-Kindi, the "Philosopher of the Arabs," as he was called (circ. 365), contains our best account of the various sects existing in Islam towards the end of the 3rd century A.H. as he met them in the course of his travels. It has been published as the second volume of De Goeje's Bibliotheca Geographorum Arab. (Leiden., 1873).
The next great philosopher was Muhammad b. Muhammmad b. Tarkhan Abu Nasr al-Farabi (d. 339), of Turkish descent. He was "a celebrated philosopher, the greatest indeed that the Muslims ever had; he composed a number of works on logic, music, and other sciences. No Musulman ever reached in the philosophical sciences the same rank as he, and it was by the study of his writings and the imitation of his style that Avicenna attained proficiency and rendered his own works so useful." (Ibn Khallikan, iii. 307). He was born at Farab or Otrar near Balasaghum, but travelled widely. In the course of his wanderings he came to Baghdad but, as at the time he knew no Arabic, he was unable to enter into the intellectual life of the city. He set himself first to acquire a knowledge of the Arabic language, and then became ​a pupil of the Christian physician Matta b. Yunus, who was at that time a very old man, and under him he studied logic. To increase his studies he removed to Harran, where he met the Christian philosopher Yuhanna b. Khailan, and continued to work at logic under his direction. He then returned to Baghdad, where he set to work at the Aristotelian philosophy, in the course of his studies reading the de anima 200 times, the Physics 40 times. His chief interest, however, was in logic, and it is on his logical work that his fame chiefly rests. From Baghdad he went to Damascus, and thence to Egypt, but returned to Damascus, where he settled for the rest of his life. At that time the empire of the Khalifa of Baghdad was beginning to split up into many states, just like the Roman Empire under the later Karlings, and the officials of the Khalifate were forming semi-independent principalities under the nominal suzerainty of the Khalif and establishing hereditary dynasties. The Hamdanids Shi'ites, who began to rule in Mosul in 293, established themselves at Aleppo in 333 and achieved great fame and power as successful leaders against the Byzantine emperors. In 334 (= 946 A.D.) the Hamdanid Prince Sayf ad-Dawla took Damascus, and al-Farabi lived under his protection. At that period the orthodox were distinctly reactionary, and it was the various Shi'ite rulers who showed themselves the patrons of science and philosophy.
​At Damascus al-Farabi led a secluded life. Most of his time he spent by the borders of one of the many streams which are so characteristic a feature of Damascus, or in a shady garden, and here he met and talked with his friends and pupils. He was accustomed to write his compositions on loose leaves, "for which reason nearly all his productions assume the form of detached chapters and notes; some of them exist only in fragments and unfinished. He was the most indifferent of men for the things of this world; he never gave himself the least trouble to acquire a livelihood or possess a habitation. Sayf ad-Dawla settled on him a daily pension of four dirhams out of the public treasury, this moderate sum being the amount to which al-Farabi had limited his demand." (Ibn Khallikan, iii. 309–310.)
Al-Farabi was the author of a series of commentaries on the logical Organon, which contained nine books according to the Arabic reckoning, namely:
| (i.) | The Isagoge of Porphyry. |
| (ii.) | The Categories or al-Maqulat. |
| (iii.) | The Hermeneutica or al-'Ibara or al-Tafsir. |
| (iv.) | The Analytica Priora or al-Qiyas I. |
| (v.) | The Analytica Posteriora or al-Burhan. |
| (vi.) | The Topica or al-Jadl. |
| (vii.) | The Sophistica Elenchi or al-Maghalit. |
| (viii.) | The Rhetoric or al-Khataba. |
| (ix.) | The Poetics or ash-Shi'r. |
As we have already noted, his primary importance was as a teacher of logic. A great deal of what he has written is simply a reproduction of the outlines of the Aristotelian logic and an exposition of its principles, but De Vaux (Avicenne, pp. 94–97) has drawn attention to evidences of original thought in his "Letter in reply to certain questions."
Like al-Kindi he accepted the Theology as a genuine work of Aristotle, and shows very clear traces of its influences. In his treatise "On the intelligence" he makes a careful analysis of the way in which the term 'aql (reason, intelligence, spirit) is employed in general speech and in philosophical enquiry. In common language "a man of intelligence" denotes a man of ​reliable judgment, who uses his judgment in an upright way to discern between good and evil, and thus is distinguished from a crafty man who employs his mind in devising evil expedients. Theologians use the term 'aql to denote the faculty which tests the validity of statements, either approving them as true or rejecting them as false. In the Analytica Aristotle uses "intelligence" for the faculty by which man attains directly to the certain knowledge of axioms and general abstract truths without the need of proof; this faculty al-Farabi explains as being the part of the soul in which intuition exists, and which is thereby able to lay hold of the premises of speculative science, i.e., the reason of intelligence proper as the term is employed in the de anima, the rational soul which Alexander of Aphrodisias takes as an emanation from God. Following al-Kindi, al-Farabi speaks of four faculties or parts of the soul: the potential or latent intelligence, intelligence in action, acquired intelligence, and the agent intelligence. The first is the 'aql hayyulani, the passive intelligence, the capacity which man has for understanding the essence of material things by abstracting mentally that essence from the various accidents with which it is associated in perception, more or less equivalent to the "common sense" of Aristotle. The intelligence in action or 'aql bi-l-fi'l is the potential faculty aroused to activity and making this abstraction. The agent intelligence or 'aql fa''al is the external power, the emanation from God which is able to awaken ​the latent power in man and arouse it to activity, and the acquired intelligence or 'aql mustafad is the intelligence aroused to activity and developed under the inspiration of the agent intelligence. Thus the intelligence in action is related to the potential intellect as form is to matter, but the agent intelligence enters from outside, and by its operation the intelligence receives new powers, so that its highest activity is "acquired."
Al-Farabi appears throughout as a devout Muslim, and evidently does not appreciate the bearing of the Aristotelian psychology on the doctrine of the Qur'an. The earlier belief of Islam, as of most religions, was a heritage from primitive animism, which regarded life as due to the presence of a perfectly substantial, though invisible, thing called the soul: a thing is alive so long as the soul is present, it dies when the soul goes away. In the earlier forms of animism this is the explanation of all movement: the flying arrow has a "soul" in it so long as it moves, it ceases to move when this soul goes away or desires to rest. This involves no belief in the immortality of the soul, nor is the soul invested with any distinct personality, all that comes later; it is simply that life is regarded as a kind of substance, very light and impalpable but perfectly self-existent. What may be described as the "ghost" theory marks a later stage of evolution, when the departed soul is believed to retain a distinct ​personality and still to possess the form and some at least of the sensations associated with the being in which it formerly dwelt. Such was the stage reached by Arab psychology at the time of the preaching of Islam. The Aristotelian doctrine represented the soul as containing different energies or parts, such as it had in common with the vegetable world and such others as it possessed in common with the lower kinds of animals: that is to say the faculties of nutrition, reproduction, and all the perceptions obtained from the use of the organs of sense, as well as the intellectual generalisations derived from the use of those senses, are simply laid on one side as forms of energy derived from the potentialities latent in the material body, very nearly the position indeed of modern materialism, as the term is used in psychology. This does not oppose a belief in God, who is the prime source of the powers which exist, although that is brought out more by the commentators than by Aristotle himself; nor does it infringe the doctrine of an immortal and separable soul or spirit which exists in man in addition to what we may describe as the vegetative and animal soul. It is this spirit, the rational soul which has entered from outside and exists in man alone, which is immortal. Such a doctrine sets an impassible gulf between man and the rest of creation, and explains why it is impossible for those whose thought is formed on Aristotelian lines, whether in orthodox ​Islam or in the Catholic Church, to admit the "rights" of animals, although ready to regard benevolent action towards them as a duty. But more, the highly abstract rational soul or spirit of the Aristotelian doctrine, void of all that could be shared with the lower creatures, and even of all that could be developed from anything that an animal is capable of possessing, is the only part of man which is capable of immortality, and such a spirit separated from its body and the lower functions of the animal soul can hardly fit in with the picture of the future life as portrayed in the Qur'an. Further, the Qur'an regards that future life as incomplete until the spirit is re-united with the body, a possibility which the Aristotelians could hardly contemplate. The Aristotelian doctrine showed the animal soul not as an invisible being but merely as a form of energy in the body: so far as it was concerned, death did not mean the going away of this soul, but the cessation of the functions of the bodily faculties, just as combustion ceases when a candle is blown out, the flame not going away and continuing to exist apart; or as the impression of a seal on wax which disappears when the wax is melted and does not continue a ghostly existence on its own account. The only immortal part of man, therefore, was the part which came to him as an emanation from the Agent Intellect, and when this emanation was set free from its association with the human body and lower soul it became inevitable to suggest its re-absorption in the ​omnipresent source from which it had been derived. The logical conclusion was thus a denial, not of a future life, nor of its eternity, but of the separate existence of an individual soul, and this, as we shall see, was actually worked out as a result of Arabic Aristotelianism. Thus the scholastic theologians, both of Islam and of Latin Christianity, attack the philosophers as undermining belief in individual personality and in opposing the doctrine of the resurrection, and in this latter, it must be remembered, Muslim doctrine is committed to cruder details than prevail in Christianity. But al-Farabi did not see where the Aristotelian teaching would lead him: to him Aristotle seemed orthodox because his doctrines seemed to prove the immortality of the soul.
Al-Farabi expresses his theory of causality in the treatise called "the gems of wisdom." Everything which exists after having not existed, he says, must be brought into being by a cause which itself may be the result of some preceding cause, and so on, until we reach a First Cause, which is and always has been, its eternity being necessary because there is no other cause to precede it, and Aristotle has shown that the chain of causes cannot be infinite. The First Cause is one and eternal, and is God (cf. Aristot. Metaph. 12. 7, and similarly Plato, Timaeus 28). Being unchanged this First Cause is perfect, and to know it is the aim of all philosophy, for obviously everything would be intelligible if the cause of all were known. This First Cause is the "necessary being" whose ​existence is necessary to account for all other existence; it has neither genus, species, nor differentia; it is both external and internal, at once apparent and concealed; it cannot be perceived by any faculty but is knowable by its attributes, and the best approach to knowledge is to know that it is inaccessible. In this treatment al-Farabi is mingling the teaching of philosophy proper with mysticism, in his days rapidly developing in Asiatic Islam, and especially in the Shi'ite community with which he was in contact. From the philosophical point of view God is unknowable but necessary, just as eternity and infinity are unknowable but necessary, because God is above all knowledge: but in another sense God is beneath all knowledge, as the ultimate reality must underlie all existing things, and every result is a manifesting of the cause.
The proof of the existence of God is founded upon the argument in Plato, Timaeus 28, and Aristotle, Metaphysics 12. 7, and was later on used by Albertus Magnus and others. In the first place a distinction is made between the possible, which may be only potential, and the real. For the possible to become real it is necessary that there should be an effective cause. The world is evidently composite, and so cannot itself be the first cause, for the first cause must be single and not multiple: therefore the world evidently proceeds from a cause other than itself. The immediate cause may itself be the result of another preceding cause, but the series of causes cannot be infinite, nor ​can they return as a circle upon themselves, therefore if we trace back we must ultimately reach an ens primum, itself uncaused, which is the cause of all, and this first cause exists of necessity, but not by a necessity caused by anything other than itself. It must be single and unchangeable, free from all accidents, absolute, perfect, and good, and the absolute intelligentia, intelligibile, and intelligens. In itself it possesses wisdom, life, insight, will, power, beauty and goodness, not as acquired or external qualities, but as aspects of its own essence. It is the first will and the first willing, and also the first object of will. It is the end of all philosophy to know this first Cause, which is God, because as He is the cause of all, all can be understood and explained by understanding and knowing Him. That the first Cause is single and one and the cause of all agrees with the teaching of the Qur'an, and al-Farabi freely uses Qur'anic phraseology in perfect good faith, supposing that the Aristotelian doctrine corroborates the doctrine of the Qur'an. The most curious part of al-Farabi's work is the way in which he employs the terminology of the Qur'an as corresponding to that of the neo-Platonists, so that the Qur'anic pen, tablet, etc., represent the neo-Platonic, etc. It may be questioned whether, even in al-Farabi, philosophy really does fit in with Qur'anic doctrine, but the divergence was not yet sufficiently marked to compel attention.
Assured of the conformity of the teaching of Aristotle with the teaching of revelation al-Farabi ​denies that Aristotle teaches the eternity of matter, and so is inconsistent with the dogma of creation. The whole question depends on what is meant by "creation." God, he supposes, created all things in an instant in unmeasured eternity, not directly, but by the intermediary operation of the 'aql or Agent Intelligence. In this sense Aristotle held that the universe existed in eternity, but it so existed as a created thing. Creation was therefore complete before God, acting through the 'aql, introduced movement, at which time commenced; as movement and time came into existence simultaneously, forthwith creation already existing in the timeless came out of its concealment and entered into reality. The term "creation" is sometimes used as applying to this emergence from timeless quiescence, but more properly may be taken as denoting the causation, which, as it preceded time, came into unmeasured eternity, which is what Aristotle means when he speaks of the world as eternal. Thus both Qur'an and Aristotle are right, but each uses "creation" to denote a different thing.
It is difficult to over-estimate the importance of al-Farabi. Practically all we afterwards meet in Ibn Sina and Ibn Rushd is already to be found in substance in his teaching, only that these later philosophers have realized that the Aristotelian system cannot be reconciled with the traditional theology, and so, having given up all attempt at formal reconciliation, are able to express themselves more clearly and to ​press home their tenets to their logical conclusions. When considering the reconciliation between philosophy and Qur'an attempted by al-Farabi it is important to compare and contrast the reconciliation attempted on quite other lines by al-Ash'ari and other founders of orthodox scholasticism. It must be noted that the beginning of scholasticism was contemporary with al-Farabi.
As has been noted, al-Farabi was mixed up with the Shi'ite group; the supporters of 'Alid claims who held aloof from the official Khalifate at Baghdad. About the time of al-Kindi's death (circ. 260), the twelfth Iman of the Ithna 'ashariya or orthodox Shi'ite sect, Muhammad al-Muntazar, "disappeared." In the year 320, within the period of al-Farabi's activity, the Buwayhid princes became the leading power in 'Iraq, and in 334, five years before his death, they obtained possession of Baghdad, so that for the next 133 years the Khalifs were in very much the same position as the Frankish kings when they, surrounded with great ceremony and treated with the utmost reverence, were no more than puppets in the hands of the Mayors of the Palace. In exactly the same way the Khalifs, half popes and half emperers, whose sign manual was sought as giving a show of legitimacy to sovereigns even in far-off India, possessed in Baghdad only ceremonial functions, and were treated as honoured prisoners by the Buwayhid Emirs, who themselves were Shi'ites of the Ithna 'ashariya sect, and who, consequently, ​regarded the Khalifs as mere usurpers. At this period the Shi'ites were the patrons of philosophy, and the orthodox Sunnis generally took a reactionary attitude.
Besides the Ithna 'ashariya, the comparatively orthodox Shi'ites, there was another branch of extremer type known as the Sab'iya or "seveners." The sixth Imam Ja'far as-Sadiq had nominated his son Isma'il as his successor, but as Isma'il was one day found drunk, Ja'far disinherited him and appointed his second son Musa al-Qazam (d. 183). But some did not admit that the Imamate, whose divine right passed by hereditary descent, could be transferred at will, but remained loyal to Isma'il, and these preferred, when Isma'il died in Ja'far's lifetime, to transfer their allegiance to his son Muhammed, reckoning him as the seventh Imam. These "seveners" continued to exist as an obscure sect until, it would appear, somewhere about the year 220, when 'Abdullah, the son of a Persian oculist named Maymun, either was made their head or led a secession from them, and organised his followers with a kind of freemasonry in seven (afterwards nine) grades of initiation and a very admirably organised system of propaganda on the lines already laid down by the Hashimites (cf. supra). In the earlier grades the doctrine of batn or allegorical interpretation of the Qur'an was laid down as essential to a right understanding of its meaning, for the literal sense is often obscure, and sometimes refers to things incomprehensible, a doctrine commonly ​attributed to Ja'far as-Sadiq. The initiate was then taught that the true meaning could not be discovered by private interpretation but needed an authoritative teacher, the Imam, or, as he had disappeared, his accredited representative, the Mahdi 'Abdullah, son of Maymun. In the higher grades the disciple had this inner meaning of the Qur'an disclosed to him, and this proved to be substantially the Aristotelian and neo-Platonic doctrine in general outline, together with certain oriental elements derived from Zoroastrianism and Masdekism. These oriental elements figured chiefly in the doctrines taught to the intermediate grades, the higher ones attaining a pure agnosticism with an Aristotelian background. The sect thus formed spread, developed, and finally divided. It had a successful career in the Bahrayn or district near the junction of the two rivers, the Tigris and Euphrates, and there its followers were known as Qarmatians, after the name of a leading missionary. It met with success also in and around Aden, but we have no account of its subsequent history there. From Aden missionaries passed over to North Africa, where it had its chief success, and when Ubayd Allah, a descendant of 'Abdullah, passed over there an independent state was founded, with its capital at Kairawan (297 A.H.). From Kairawan a missionary propaganda was conducted in Egypt, then suffering from almost perennial misgovernment, and in the days of the deputy Kafur a definite invitation was sent by the Egyptian officials asking for the Khalif ​of Kairawan to enter Egypt. At length Ubayd Allah's great-grandson al-Mo'izz did invade Egypt in 356, and established there the Fatimite Khalifate, which lasted until the country was conquered by Saladin in 567.
The Sab'iya sect was thus geographically divided into two branches, one in Asia represented by the Qarmatians, the other in Africa under the Fatimite Khalifs. In the Asiatic branch the members were chiefly drawn from the Nabatæan peasantry, and the sect took the form of a revolutionary group with communist teaching, and violently opposed to the Muslim religion. In their contemptuous hostility they finally attacked Mecca, slew many of the dignitaries of the city and a number of pilgrims who were there, and carried off the sacred black stone, which they retained for several years. In the hands of the Qarmatians the sect ceased to be a propaganda of philosophical doctrine, it became simply anti-religious and revolutionary. The history of the African branch took a different turn. Possession of an important state brought with it a position of respectability, and political ambition replaced religious enthusiasm. As the majority of the subject population was strictly orthodox, the peculiar tenets of the sect were, to a large extent, allowed to drop into the background; candidates were still admitted to initiation and instructed, but, although the Fatimite rulers in Egypt were liberal patrons of scholarship, and generally showed a more tolerant attitude than ​other contemporary Muslim rulers, they certainly did not carry out a wholesale Aristotelian propaganda; indeed, the line of "philosophers" proper simply misses over Fatimite Egypt, although there were several distinguished medical workers there. From the Isma'ilians or Sab'iya of Egypt there came two interesting off-shoots. Towards the end of the reign of the sixth Fatimite Khalif, al-Hakim, who may have been a religious fanatic, perhaps insane, or possibly an enlightened religious reformer of views far ahead of his age—his real character is one of the problems of history—there arrived in Egypt certain Persian teachers holding doctrines of transmigration and of theophanies, which seem to be endemic in Persia, and these persuaded al-Hakim that he was an incarnation of the Deity. A riot followed the open preaching of this claim, and the preachers fled to Syria, then a part of the Fatimite dominions, and there founded a sect which still exists in the Lebanon under the name of the Druzes. Soon after this al-Hakim himself disappeared; some said he was murdered, others said he had retired to a Christian monastry, and was recognised there afterwards as a monk; others believed he had gone up to heaven, and more than one claimant appeared asserting that he was al-Hakim returned from concealment. The other off-shoot shows a more definitely philosophical bearing. In the days of al-Mustansir, al-Hakim's grandson, one of the Isma'ilian missionaries, a Persian named Nasir-i-Khusraw, came from Khurasan ​to Egypt, and after a stay of seven years returned home. This seems to have coincided with a kind of revival in the Isma'ilian sect, which now regarded Cairo as its headquarters. The Qarmatians had quite passed away; al-Hakim, whatever his later eccentricities, had been a patron of scholarship, the founder of an academy, the Daru l-Hikma, or "House of Wisdom," at Cairo, and had enriched it with a large library, and was himself distinguished as a student of astronomy. The reign of his grandson was the golden age of Fatimid science, and apparently Shi'ites from all parts of Asia found their way to Egypt. In 471 another da'i or missionary, Hasan-i-Sabbah, a pupil of Nasir-i-Khusraw, visited Cairo and was received by the Chief Da'i, but not allowed to see the Khalif, and eighteen months later was compelled to leave the country and return to Asia. There were two factions in Cairo, the adherents respectively of the Khalif's two sons, Nizar and Musta'li; Nasir-i-Khusraw and Hasan-i-Sabbah had already made themselves known as supporters of the elder son Nizar, but the court officials in Egypt adhered to the younger son Musta'li. When the Khalif al-Mustansir died in 487 the Isma'ilian sect divided into two new branches, the Egyptians and Africans generally recognising Musta'li, the Asiatics adhering to Nizar This latter group had already been well organised by Nasir-i-Khusraw and Hasan-i-Sabbah, who for several years previously had been preaching the rights of Nizar. On his return home, about 473, ​Hassan-i-Sabbah had secured possession of a stronghold known as Alamut, "the eagle's teaching" (cf. Browne: Lit. History of Persia, ii. 203, espec. note 13), and this became the headquarters of the sect of Nizaris or Assassins, who figure so prominently in the history of the Crusades. They had many mountain strongholds, but all were under the control of the Sheikh or "Old Man of the Mountain," as the Crusaders and Marco Polo called him, at Alamut. These Sheikhs or Grand Masters of the order continued for eight generations, until Alamut was captured by the Mongols in 618 A.H. (= 1221 A.D.), and the last was put to death. As the order grew it spread into Syria, and it was the Syrian branch with which the Crusaders from Europe came most into contact. In this order we find the old system of successive grades of initiation. The Lasiqs, or "adherents," had but little knowledge of the real doctrines of the sect, and attached to them were the Fida'is or "self-devoted," bound to blind obedience and ready to execute vengeance at the bidding of their superiors; these were the men to whom the Crusaders especially applied the term Assassins, that is Hashishin or "users of hashish," referring to the hashish or Indian hemp which they commonly used as a means of exaltation. Above these were the Rafiqs or "companions," and above these was an ordered hierarchy of da'is or missionaries, Chief Missionaries (da'i i-Kabir), and Supreme Missionary (da'i d-Du'at). In the eyes of outsiders the whole sect had a sinister ​appearance; the crimes of the Fida'is, usually committed under striking and dramatic circumstances, and the reputed heresies of the superior grades were sufficient to secure this, and the general dread with which they were regarded was increased by incidents which showed that they had spies and sympathizers in all directions. The superior grades, however, were true heirs of the old Isma'ilian principles and ardent students of philosophy and science. When the Mongols under Hulagu seized Alamut in 654 = A.D. 1256) they found an extensive library and an observatory with a collection of valuable astronomical instruments. The Mongol capture meant the downfall of the Assassins, although the Syrian branch still continued in humbler fashion, and the sect has adherents even at the present day. Scattered relics survive also in central Asia, in Persia, and in India; the Agha Khan is a lineal descendant af Ruknu d-Din Khurshah, the last Sheikh at Alamut.
Thus the movement started by Abdullah, the son of Maymun, whose original purpose seems to have been to maintain a highly philosophical religion as revealed by Aristotle and the neo-Platonists, but to safeguard this as an esoteric faith disclosed only to initiates, the rank and file being apparently Shi'ite sectaries, produced a group of very curious sects. In the Qarmatians the esoteric tenets were compelled to take a debased form because those who professed them, and into whose hands this branch fell altogether, were illiterate peasants. In the Fatimid ​state of Egypt they were minimised because political considerations rendered it expedient to conciliate orthodox Muslim opinion. And in the Assassins, confined, it seems, to the higher grades of the initiates, they produced a rich intellectual development, though allied to a system which shows fanaticism unscrupulously used by the leaders that they might live out their lives in a philosophical seclusion, protected from the dangers which surrounded them.
Before leaving this particular subject, which shows the promulgation of philosophy as an esoteric creed, we must refer to a society known as the Ikhwanu s-Safa or "the brotherhood of purity." We do not know what its connection with 'Abdullah b. Maymun's sect may have been beyond the fact that they were contemporary and of kindred aims, but it certainly seems that there was some connection: it has been suggested that this brotherhood represents the original teaching of Abdullah's sect. It was divided into four grades, but its doctrines were promulgated freely at an early date, though we do not know whether this general divulging of its teaching was part of the original plan or forced upon it by circumstances. It appears openly about 360, some hundred years after Abdullah founded his sect, shortly after the Fatimites had conquered Egypt and some time after the Qarmatians had returned the sacred black stone which they had stolen from the "House of God" at Mecca. It seems tempting to suggest that it may have been a reformation of ​the Ishma'ilians on the part of those who wished to return to the original aims of the movement.
The published work of the brotherhood appears in a series of 51 epistles, the Rasa'il ikhwani s-Safa, which form an encyclopædia of philosophy and science as known to the Arabic-speaking world in the 4th cent. A.H. They do not propose any new theories but simply furnish a manual of current material. The whole text of these epistles has been printed at Calcutta, whilst portions of the voluminous whole have been edited by Prof. Dieterici between 1858 and 1872, and these were followed in 1876 and 1879 by two volumes called Makrokosmos and Mikrokosmos, in which an epitome is presented of the whole work. It appears that the leading spirit in the preparation of this encyclopædia was Zayd b. Rifa'a, and with him were associated Abu Sulayman Muhammad al-Busti, Abu l-Hasan 'Ali az-Zanjani, Abu Ahmad al-Mahrajani, and al-Awfi, but it does not follow that these were the founders of the brotherhood, as some have supposed.
A great part of the Epistles of the Brotherhood deals with logic and the natural sciences, but when the writers turn to metaphysics, psychology, or theology, we find very clear traces of the neo-Platonic doctrines as contained in Alexander of Aphrodisias and matured by Plotinus. God, we read, is above all knowledge and above all the categories of human thought. From God proceeds the 'aql or intelligence, a complete spiritual emanation which contains in itself the forms ​of all things, and from the 'aql proceeds the Universal Soul, and from that Soul comes primal matter: when this primal matter becomes capable of receiving dimensions it becomes secondary matter, and from that the universe proceeds. The Universal Soul permeates all matter and is itself sustained by the perpetual emanation of itself from the 'aql. This Universal Soul permeating all things yet remains one; but each individual thing has a part-soul, which is the source of its force and energy, this part-soul having a varying degree of intellectual capacity. The union of soul and matter is temporary; by wisdom and faith the soul tends to be set free from its material fetters, and so to approach nearer to the present spirit or 'aql. The right aim of life is the emancipation of the soul from matter, so that it may be absorbed in the parent spirit and thus approach nearer to the Deity. All this is but a repetition of the teaching of al-Farabi and the neo-Platonists, slightly coloured, perhaps, by Sufism, and expressed less logically and lucidly than in the teaching of the philosophers. In general character it shows a tendency towards pantheism, akin to the tendency we have already observed in certain of the Mu'tazilites. God, properly so called, is outside, or rather on such a plane that man does not know, and never can know, anything about Him. Even the 'aql is on a plane other than that on which the human soul lives. But the Universal Soul which permeates all things is an emanation from this Spirit, and the Spirit emanates ​from the unknowable God. Comparing this with the teaching of al-Kindi and al-Farabi it is clear that it is based upon the same material, but it is in the hands of those who have made it a religion, and this religion has entirely broken away from the orthodox doctrine of the Qur'an. In al-Farabi this breach is not conscious, although really quite complete; in his successors we see a full realization of the cleavage. Comparing it with Sufism the superficial resemblances are very close, the more so as Sufism borrows a great deal of philosophical, i.e., neo-Platonic terminology, but in fact there is an essential divergence: the Epistles of the brethren represent the emancipation of the soul from matter as the aim of life, and the final result is re-absorption in the Universal Soul, but they represent this emancipation as due to an intellectual force, so that the soul's salvation lies in wisdom and knowledge; it is a cult of intellect. But Sufism is spiritual in another sense: it has the same aim in view, but it regards the means as wisdom in the sense of religious truth as found by the devout soul in piety, not as the wisdom obtained by intellectual learning.
We seem, however, justified in saying that Sufism is the heir of the philosophical teaching of al-Farabi and the Brethren of Purity, at least in Asia. After the first quarter of the fifth century philosophical teaching seems to have disappeared altogether in Asia, but this is only apparent. In substance it remains in Sufism, and we may say that the essential ​change lies in the new meaning given to "wisdom," which ceases to signify scientific facts and speculations acquired intellectually, and is taken to mean a supra-intellectual knowledge of God. This, perhaps, represents the Indian contribution working upon elements of Hellenistic origin.
The doctrines of the Brethren of Purity were introduced to the West by a Spanish doctor, Muslim b. Muhammad Abu l-Qasim al-Majriti al-Andalusi (d. 395–6), and were largely influential in producing the falasifa of Spain, who ultimately exercised so great an influence on mediæval Latin scholasticism.
Before leaving this particular section of our subject it will be well to note that all these sects and groups we have mentioned after al-Farabi, from the sect founded by Abdullah b. Maymun to the Brethren of Purity, agreed in treating philosophy, at least in so far as it had any bearing on theological topics, as esoteric, and not to be disclosed to any save the elect. This general attitude will appear again, in a slightly different form, in the works of the Spanish philosophers, and to some extent recurs in all Islamic thought.
The greatest product in Asia of the ferment of thought produced by the general study of the Aristotelian and neo-Platonic philosophies appears in Abu 'Ali al-Husayn b. 'Abdullah b. Sina (d. 428 = A.D. 1027), commonly known as Ibn Sina, which is Latinized as Avicenna. His life is known to us from an autobiography completed by his pupil, Abu Ubayd ​al-Juzjanl, from his master's recollections. We learn that his father was governor of Kharmayta, but, after his son's birth, he returned to Bukhara, which had been the original home of his family, and it was there that Ibn Sina received his education. During his youth some Isma'ilian missionaries arrived from Egypt, and his father became one of their converts. From them the son learned Greek, philosophy, geometry, and arithmetic. This helps to remind us how the whole Isma'ilian propaganda was associated with Hellenistic learning. It is sometimes stated that the Egypt of the Fatimite age was isolated from the intellectual life of Islam at large: but this is hardly accurate; from first to last the whole of the Isma'ilian movement was connected with the intellectual revival due to the reproduction of Greek philosophy in Arabic form, less so, of course, when the Isma'ilian converts were drawn from the illiterate classes, as was the case with the Qarmatians, and when the attention of the members was engrossed with political ambitions, as was the case with the Fatimids whilst they were building up their power in Africa before the invasion of Egypt. But even under the most unfavourable conditions it seems that the da'is or missionaries regarded the spread of science and philosophy as a leading part of their duties, quite as much so as the preaching of the 'Alid claims of the Fatimite Khalif. Learning Greek and Greek philosophy from these missionaries Ibn Sina made rapid progress, and then turned to the study of ​jurisprudence and mystic theology. Jurisprudence, that is to say, the canon law based on one of the orthodox systems laid down by Ab-u Hanifa and the other recognised jurists, or by their Shi'ite rivals, has always been the backbone of Islamic scholarship, and was thus parallel with the study of canon law in mediæval Europe: in each case it turned men's attention to the development of the social structure towards an ideal, and this had an educative influence of the highest value. We, holding very different principles, may be tempted to under-estimate this influence, but it is worth noting that, whilst our aims are opportunist in character, the canonist of Islam or of Christendom had a more definitely constructed ideal, with a more complete and scientific finality, which, in so far as it was an ideal, was an uplifting power. In Muslim lands the canonists were the one power which had the courage and ability to resist the caprices of an autocratic government, and to compel even the most arbitrary princes to submit to principles which, however narrow and defective they may seem to us, yet made the ruler admit that he was subordinate to a system, and defined the limits allowed by that system in conformity with ideals of equity and justice. It is interesting to note that in Ibn Sina's time mystic theology had already taken its place as a subject of serious study.
A short time afterwards a philosopher named an-Natali arrived at Bukhara and became a guest of Ibn Sina's father. Bearing in mind the technical ​meaning of failasuf, we recognise this guest as a professed Aristotelian, and presumably one able to obtain his living as a teacher of the Aristotelian doctrine. From him Ibn Sina learned logic and had his mind directed towards the Aristotelian teaching, which was then preached like a religion. After this he studied Euclid, the Almajesta, and the "Aphorisms of the Philosophers." His next study was medicine, in which he made so great progress that he adopted the practice of medicine as his profession. He attempted to study Aristotle's Metaphysics, but found himself entirely incapable of understanding its meaning, until one day he casually purchased one of al-Farabi's books, and by its help he was able to grasp the meaning and purport of what had so far eluded him. It is on this ground that we are entitled to describe Ibn Sina as a pupil of al-Farabi: it was al-Farabi's work which really formed his mind and guided him to the interpretation of Aristotle; al-Farabi was, in the truest sense, the parent of all subsequent Arabic philosophers; great as was Ibn Sina, he does not enter into the tradition in the same way as al-Farabi, and does not exercise the same influence on his successors, although al-Ghazali classes him with al-Farabi, and calls them the leading interpreters of Aristotle. Emphasis is sometimes laid upon the fact that Ibn Sina treats philosophy as quite apart from revelation as given in the Qur'an; but in this he was not original: it was the general tendency of all who came after al-Farabi; we can ​only say that Ibn Sina was the first important writer who illustrates this tendency.
Called to exercise his medical skill at the court of Nuh b. Mansur, the Samanid governor of Khurasan, he enjoyed that prince's favour, and in his library studied many works of Aristotle hitherto unknown to his contemporaries, and when that library was burned he was regarded as the sole transmitter of the doctrines contained in those books. This represents contemporary Arabic opinion about him: there is no evidence in his existing writings that he had access to Aristotelian material other than that generally known to the Syriac and Arabic writers. When the affairs of the Samanid dynasty fell into disorder Ibn Sina removed to Khwarazan, where he, with several other scholars, enjoyed the enlightened patronage of the Ma'muni Emir. But this Emir was living a somewhat precarious existence in the neighbourhood of the Turkish Sultan Mahmud of Ghazna, the stern champion of orthodoxy and the conqueror of India. It was obvious that the Sultan coveted the Emir's dominions, and that when he chose to seize them it would be impossible to resist; he actually did take them in 408. Meanwhile the Sultan was treated with the utmost deference by the Emir and such of his neighbours as were allowed to live on sufferance. Mahmud wished to be distinguished as a patron of learning, and "invited" scholars to his court—in plain words, he kidnapped scholars and took care that they never afterwards transgressed the strictest ​limits of orthodoxy. Amongst others the Emir received a letter inviting such men of learning as were to be found in Khwarazan to his court. The Emir read out the letter to the five most distinguished scholars who were his guests, leaving them to act as they thought fit. Three of the guests were attracted by the Sultan's reputation for generosity and accepted the invitation, but two, Ibn Sina and Masihi, were afraid to venture, so they escaped privately and fled; overtaken by a sandstorm in the desert Masihi perished, but Ibn Sina, after long wanderings, finally found a refuge in Isfahan, where the Buwayhid 'Ala'u d-Dawla Muhammad held his court. His experiences show plainly that it was the Shi'ites who were the supporters of philosophy, and that the growing Turkish power of Mahmud of Ghazna and of the Seljuks who succeeded him was reactionary and unfavourably disposed towards philosophical research. It was the Turkish power which finally checked the progress of Arabic philosophy in the East.
Ibn Sina wrote many works in Arabic and Persian, and a number of these are still extant. Amongst his productions were as-Shafa, an encyclopædia of physics, metaphysics, and mathematics in eighteen volumes (ed. Forget, Leiden, 1892), a treatise on logic and philosophy, and the medical works on which his fame so largely rests. The best known of these are the Najat abridged from the as-Shafa, and the medical Canon, in which he reproduced the teaching ​of Galen and Hippocrates with illustrative material from the later medical writers. The Canon is more methodical in its arrangement than the al-Hawi of Razes, hitherto the popular manual of medicine in Arabic; indeed, its chief defect is an excessively elaborate classification. It became the leading medical authority, and, after translation into Latin by Gerard of Cremona, served for many centuries as the chief representative of the Arabic school of medicine in western Europe, holding its place in the universities of Montpelier and Louvain down to A.D. 1650.
Ibn Sina treats logic as of use rather in a negative than in a positive way: "the end of logic is to give a man a standard rule, by observing which he is preserved from error in reasoning" (Isharat ed. Forget, p. 2). His treatise on this subject in Tis' Rasa'il fi-l-Hikma wa-l-Tabi'yat (p. 79, pub. Stamboul, 1298), is divided into nine parts corresponding to the Arabic canon of Aristotle, which includes the Isagoge as well as the Rhetoric and Poetics. He makes special note to the logical bearing of particular grammatical constructions which in Arabic differ from the forms used in Greek, as, for example, where the Greek expresses the universal negative by "all A is not B," but Arabic renders this "nothing of A (is) B." He lays great emphasis upon accurate definition, which he describes as the essential basis of all sound reasoning, and to this he devotes much attention. Definition proper must state the quiddity ​of a thing, its genus, differentia, and all its essential characteristics, and is thus distinct from mere description, which need only give the propria and accidents in such a way that the thing may be recognised correctly.
In dealing with the universal and the particular he considers that the universal exists only in the human mind: the abstract idea of the genus is formed in the mind of the observer when he compares individuals and makes note of their points of similarity, but this abstract idea exists only as a mental concept and has no objective reality. The universal precedes the individual (genus ante res) only in the way that the general idea existed in the mind of the Creator before the individual was formed, just as the idea of an object to be made exists in the mind of the artificer before the work is executed. The general idea is realised in matter (genus in rebus), but only when accompanied by accidents: apart from these accidents it exists only as a mental abstraction. After the general idea is realised in matter (genus post res) it is possible for the intellect to make a mental abstraction and to use this as a standard of comparison with other individuals. The generic belongs only to the realm of thought, and such abstract ideas have no objective existence, although they may be used as real in logic.
The soul is treated as a collection of faculties (kowa) or forces acting on the body: all activity of any sort, in bodies animal or vegetable, as well as human, proceeds either from such forces added to ​the body or from the mixture of elements from which the body is formed. The simplest soul condition is that of the vegetable whose activity is limited to nutrition and generation and accretion by growth (Najat, p. 43). The animal soul possesses the vegetable faculties but adds to them others, and the human soul adds yet others to these, and the addition made to the human soul enables it to be described as a rational soul. The faculties present in the soul may be divided into two classes, the faculties of perception and the faculties of action. The faculties of perception are partly external and partly internal: of these the external faculties exist in the body wherein the soul dwells and are the eight senses, sight, hearing, taste, smell, perception of heat and cold, perception of dry and moist, perception of resistance as by hard and soft, and perception of rough and smooth. By means of these senses the form of the external object is reproduced in the soul of the percipient. There are four internal faculties of perception: (i.) al-musawira, "the formative," whereby the soul perceives the object without the aid of the senses as by an act of imagination; (ii.) al-mufakkira, "the cogitative," by which the soul perceiving a number of qualities associated together abstracts one or more of them from the others with which they are associated, or groups together those which are not seen as connected; this is the faculty of abstraction which is employed in forming general ideas; (iii.) al wahm, or "opinion," by means of which ​a general conclusion is drawn from a number of ideas grouped together; and (iv.) al-hafiza or az-zakira, "memory," which preserves and records the judgments formed. Men and animals perceive pariculars by means of sense; man attains the knowledge of universals by means of reason. The 'aql or rational soul of man is conscious of its own faculties, not by means of an external, i.e., bodily sense, but immediately by the exercise of its own reasoning power. This proves to be an independent entity, even though accidentally connected with a body and dependent on that body for sense perception: the possibility of direct knowledge without sense perception shows that it is not essentially dependent on the body, and the possibility of its existence without the body, which follows logically from its independence, is the proof of its immortality. Every living creature perceives that it has only one ego or soul in itself, and this soul, says Ibn Sina, did not exist prior to the body but was created, that is to say, proceeded by emanation from the Agent Intellect at the time when the body was generated. (Najat, p. 51).
Under the head of Physics Ibn Sina considers the forces observed in nature, including all that are in the soul, save only that which is peculiar to the rational soul of man. These forces are of three kinds: some, such as weight, are an essential part of the body in which they occur; others are external to the body on which they act, and are such as cause movement ​or rest; and others, again, are such as the faculties possessed by the non-rational souls of the spheres, which produce movement directly without external impulse. No force is infinite; it may be increased or diminished, and always produces a finite result.
Time is regarded as essentially dependent on movement; although it is not itself a form of movement, so far as the idea of time is concerned, it is measured and made known by the movements of the heavenly bodies. Following al-Kindi place is defined as "the limit of the container which touches the contained." Vacuum is "only a name", in fact it is impossible, for all space can be increased, diminished, or divided into parts, and so must contain something capable of increase, etc.
God alone is "necessary being," and so the supreme reality. Space, time, etc., belong to "actual being," and whatever necessity they possess is derived from God. The objects studied in physical science are only "possible being," which may or may not become "actual being." God alone is necessarily existent through all eternity: He is the truth in the sense that He alone is true absolutely, all other reality is so only in so far as it is derived from God. From God by emanation comes the 'aql or "Agent Intellect," and from this proceeds the intellect or reason which differentiates the rational soul in man from the soul in other creatures. To every man this intellect is given, and in due course it returns to the "Agent Intellect" which was its source. The soul's possible ​activity, independent of the body with which it is associated, proves its immortality, but this immortality does not imply separate existence, but rather re-absorption in the source. From the 'aql also proceeds the universe, but not like the reason of man by direct emanation, but by the medium of successive emanations.
Ibn Sina was the last of the great philosophers of the East. Two causes combined to terminate philosophy proper in Asiatic Islam. In the first place it had become closely identified with the Shi'ite heresies, and was thus in bad repute in the eyes of the orthodox; whilst the Shi'ite sects themselves, all of the extremer kind (ghulat), which had devoted themselves most to philosophical studies, had also taken up a number of pre-Islamic religious theories, such as transmigration of souls, etc., which were detrimental to scientific research. Neo-Platonism had shown itself at an earlier period prone to similar tendencies. As a result the Shi'ites tended towards mystic and often fantastic theories, which were discouraging to the study of Aristotelian doctrines. The second cause lay in the rise of dominant Turkish elements, Mahmud of Ghazna, then the Saljuk Turks, which were of uncompromising orthodoxy, and abhorred everything which was associated with the Shi'ites or tended to rationalism. For all that it left permanent marks in Asiatic Islam in two directions: in orthodox scholasticism and in mysticism.
​We have already noted that Muslim b. Muhammad Abu l-Qasim al-Majriti al-Andalusi (d. 395–6), as his name denotes, a native of Madrid, brought the teachings of the Brethren of Purity to Spain, and so incidentally aroused an interest there in the philosophy which had been studied in the East. For some time no important results appeared, then followed a series of brilliant philosophical writers and teachers, deriving their inspiration partly from the Brethren, and partly from the Jewish students.