"Aristotle believed that the outermost stars are carried around us on a transparent sphere. In the Aristotelian view, there are directions in the universe and a preferred direction of rotation. The sun, moon, and planets are carried on different revolving spheres. The spheres and celestial bodies are composed of an everlasting fifth element, which can be destroyed by none of the ordinary contrary properties like heat and cold. It is able only to rotate in a uniform manner. This creates problems as to how the heavenly bodies create light and, in the case of the sun, heat." "The main value of Simplicius' commentary to On the Heavens 2.1-9 arises from its preservation of the lost comments of Alexander and of the controversy between Alexander and Simplicius. The two of them discuss not only the problem mentioned, but also whether soul and nature move the spheres as two distinct forces or as one. Alexander appears to have simplified Aristotle's system of fifty-five spheres down to seven, and some hints may be gleaned as to whether, simplifying further, he thinks there are seven ultimate movers or only one."--BOOK JACKET.