In chapters 12-18 of Against Proclus, Philoponus continues to do battle against Proclus' arguments for the beginninglessness and everlastingness of the ordered universe. In this final section there are three notable issues under discussion. The first concerns the composition of the heavens and its manner of movement. Philoponus argues against the Aristotelian thesis that there is a fifth heavenly body that has a natural circular motion. He concludes that even though the celestial region is composed of fire and the other three elements, it can move in a circle by the agency of its soul,...