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 reabsorption 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-Juzjani, 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 Abu 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 Almagesta, 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.