Among the Arabian philosophers of the East the most prominent were Abu Jusuf Ja'Kub ben Ishak al-Kendi (d. about 870), Abu Nasr Mohammed al-Farabi (d. 950), Abu Ali ibn Abdallah Ibn Sina (Avicenna, 980-1037) and Abu Hamed Mohammed Al Ghazali. Of the 200 treatises which Al-Kendi is said to have composed on all themes of science and philosophy, there remained only a few works on medicine and one on the astro logical-astronomy of his age, in which he ex presses the opinion that all things are bound together by harmonious causal relations, that each, when completely conceived, must repre sent as in a mirror the whole universe. Al Farabi gave the tone and direction to nearly all subsequent speculations among the Arabi ans, and his works on logic became authorita rive among the Latin schoolmen. Among the contents of his metaphysics mention is to be made of his proof of the existence of God, which was employed by Albertus Magnus and later philosophers. Taking for base the Aristotelian principle that all change and all development must have a cause, Al-Farabi distinguishes between that which has a possible and that which has a necessary existence. If the possible is to exist in reality, a cause is necessary thereto. As the world is a com posite it must have had a beginning or was caused; but as the series of causes and effects can neither recede in infinitum, nor return like a circle into itself, it must depend on some necessary link, and this link is the first being (ens primum). This first being exists necessarily; it is the cause of all that exists. It is simple and unchangeable. In his teach ing respecting that which is caused from God, Al-Farabi follows the neo-Platonists. His fundamental conception• is expressed by the word emanation. Prophecy is in Al-Farabi's opinion merely a natural manifestation of the intellect. It emanates from a soul of purified reasoning powers; the soul associates itself with the active reason and receives from it aid and instruction.Man's supreme aim is to elevate his capabilities to the highest degree of perfection attainable. Contemporary with Al-Farabi was the semi-religious and semi philosophical society of the °Brethren of Purity. ° The treatises of this society afford a kind of encyclopedic survey of the sciences of all nations and religions known to their time. Their philosophy of nature, however, ends almost entirely in psychology. The soul is the real being of man which has developed on a mystic path of ascent from the lower natural orders through the animal stage to an increasingly higher grade of perfection.
Avicenna exercised a great influence in Europe both by his medical canon and by his works on logic and metaphysics. In the domain of the latter he set out from the doctrines of Al-Farabi, but modified them by omitting many neo-Platonic theorems and approximating more nearly to the real doc trine of Aristotle. He taught that while all things are primarily traceable to the agency of an immediate influence of such a diety, inasmuch as the immutable cannot itself create substances subject to the element of change, the first and only immediate product of God is the intelligentia prima, from which the chain of emanations extended through the various celestial spheres down to our earth. But the issuing of the lower from the higher is to be conceived not as a single, temporal act, but as an eternal act. The cause which gave to things their existence must continually maintain them in existence. However, not
withstanding its dependence on God, the world has existed from eternity. Time and motion always were. Avicenna distinguishes a twofold development of our potential under standing into actuality, the one depending on instruction, the other rare and dependent on immediate divine illumination.
Ghazali, the last philosopher of the East, marked a reaction of the exclusive religious principles of Mohammedanism against philo sophical speculation. After having expounded in his 'Malcasid al-Filasafah' (Tendencies of the Philosophers) the teachings of the Peri patetics, he shows in al-Filasafah' (Destruction of the Philosophers) their weak ness. He makes a critical analysis of 20 points-16 of which belong to the domain of metaphysics, and four to that of physics— and demonstrates their contradictions. Like the Motekallamin he rejects the theory of causality, and asserts that there is not neces sarily any connection between phenomena that usually occur in a certain order. This indict ment against liberal thought was afterward refuted by Averroes, who reproaches Ghazali with duplicity; but it sounded the death knell of the study of philosophy in the East.
The Arabian philosophers of the West showed greater independence than their pred ecessors of the East and freed themselves more from the theological bias. The first among them was Avicebrol who, considered by the Christian scholastics as an Arabian, was identified by modern scholars with the Jewish famous poet Ibh Gabirol. His main thesis in his work, which was rendered into Latin in 1150 under the title 'Fons Vita,' is that the materia universalis is the substratum of all that exists; one and the same matter runs through the whole universe from the highest limits of the spiritual down to the lowest limits of the physical, excepting that matter the further it is removed from its first source becomes less and less spiritual. Though essen tially a neo-Platonist, Avicebrol departed from the pantheistic emanation doctrine, originat ing that of the divine will.
An exponent of a purer Aristotelianism was Abu Bekr Mohammed ben Jahya Ibn Badja (d. 1138), known to the Latin world as Avempace. Besides commenting on various physical treatises of Aristotle, he composed the 'Conduct of the Solitary,' in which he treats of the degrees by which the soul rises from that instructive life which it shares with the lower animals through gradual emancipa tion from materiality and potentiality to the acquired intellect, which is an emanation from the active intellect or Deity. This idea is more fully developed by Abu Bekr Mohammed ben Abd al-Malik Ibn Tofail (1100-85) known as Abubacer, in his philosophical novel 'Hay ben Jokdan) (the Living, the Son of the Waking One). Borrowing from Avicenna the allegorical character of the ideal man Hay ben Jokdan, Ibn Tofail describes the development of a thinker growing up far from all human intercourse on a lonely island. He creates for himself the conditions of material exist ence, and in his mature age is led by the contemplation of nature to the vision of God. He then meets a philosopher who has risen beyond the limitations of human society, and the two resolve to communicate this pure knowledge to the people; soon, however, they realize the vanity of the undertaking, as the people are ripe only for Mohammed's allegories.