The Greek term Apeiron, meaning originally "boundless" rather than "infinite," was used by Anaximander for the ultimate source of his universe. He probably meant by it something spatially unbounded, but since out of it arose the primary opposite substances (such as the hot and the cold, the dry and the wet) it may have been regarded also as qualitatively indeterminate. Aristotle, summarizing the views of certain early Pythagoreans (Metaphysics A, 5), puts the pair Peras ("Limit") and Apeiron ("Unlimited") at the head of a list of ten opposites. Peras is equated with (numerical) oddness, unity, rest, goodness, and so on; Apeiron is equated with evenness, plurality, motion, badness. The two principles Peras and Apeiron constituted an ultimate dualism, being not merely attributes but also themselves the substance of the things of which they are predicated. From the Pythagoreans on, the opposition of Peras and Apeiron was a...