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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 Almajesta 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