 John Philoponus  (c. 490–570s), a Monophysite Christian who studied at the still pagan School of Alexandria, was eager to show, using their own tools, that his masters were wrong about the eternity of the world. According to his argument, taken up later in the Middle Ages, the world’s eternity is incompatible with Aristotle’s own principles. Aristotle held that there could not be an actual infinity: the infinity of days that precedes today if the world is eternal is merely potential. Philoponus claims, however, that, because each day is countable, an eternity of past time would be actually infinite. Since that is impossible, the world must have had a beginning (Philoponus, On Aristotle Physics 3 [1994: 428–430, 467–478] and Against Aristotle on the Eternity of the World [1987: 143–146]; Sorabj 1983: 214–215)