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 al-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. He also wrote an “Introduction to Logic” and an “Abridgment of Logic”; indeed, as we have already noted, his main work lay in the exposition of logic. He took some interest in political science and edited a summary of the laws of Plato, which very often replaces the Politics in the Arabic Aristotelian canon. In Ethics he wrote a commentary on the Nicomachæan Ethics of Aristotle, but ethical theory did not, as a rule, appeal greatly to Arabic students. In natural science he was the author of commentaries on the _Physics_, _Meteorology_, _de coelo_ et _de mundo_ of Aristotle, as well as of an essay “On the movement of the heavenly spheres.” His work in psychology is represented by a commentary on Alexander of Aphrodisias’ commentary on the _De Anima_, and by treatises “On the soul,” “On the power of the soul,” “On the unity and the one,” and “On the intelligence and the intelligible,” some of which afterwards circulated in mediæval Latin translations, which continued to be reprinted well into the 17th century (e.g., De intelligentia et de intelligibili. Paris, 1638). In metaphysics he wrote essays on “Substance,” “Time,” “Space and Measure,” and “Vacuum.” In mathematics he wrote a commentary on the _Almagesta_ of Ptolemy, and a treatise on various problems in Euclid. He was a staunch upholder of the neo-Platonic theory that the teaching of Aristotle and that of Plato are essentially in accord and differ only in superficial details and modes of expression; he wrote treatises “On the agreement between Plato and Aristotle” and on “The object before Plato and Aristotle.” In essays “Against Galen” and “Against John Philoponus” he criticised the