  These two points bring us to a more extensive use of Philoponus by al-Kindi, in the latter’s well-known argument that the world is not eternal (for which see Davidson 1969 and 1987, and Staley 1987). Most Greek philosophers followed Aristotle in holding that the world is eternal, meaning not only that it will never cease to exist, but that it has always existed. This was the doctrine of Aristotle and the Stoics, and also of orthodox Neoplatonists, who interpreted Plato’s Timaeus as likewise committed to the past eternity of the world. Philoponus was an exception to this rule. In a work rebutting the Neoplatonist Proclus’ arguments in favor of the world’s eternity, he argued at great length that Plato’s Timaeus rightly envisions a world with a beginning in time. And in another work directed against Aristotle, Philoponus tried to undermine the arguments of the De Caelo and Physics by which Aristotle had shown that the world is eternal.