 Suppose universals were things in the world, so that one and the same item is completely present in both Socrates and an ass at the same time, making each to be wholly an animal. Abelard points out that then the same thing, animal, will be simultaneously rational (due to its role in constituting the species human being) and irrational (due to its role in constituting the species ass). But then contraries are simultaneously present in the same thing as a whole, which is impossible.