The teaching of Parmenides leads to a denial of difference or multiplicity as well as of genesis or a condition intermediate between Being and Nothing. Conversely, Aristotle denies the radical separation of Being and Nothing, or affirms genesis. Unity and difference are for him accordingly abstractions from genesis, or the result of considering the generated individual thing now in one way, now in another. The importance of accounting for genesis is given paradigmatic focus in Aristotle's Metaphysics. By his quarrel with the Megarian school of Eleatic thinkers. It seems at first glance that the Megarians deny the fact of genesis because, as Aristotle puts it, they deny the distinction between actuality and potentiality. The doctrine of predication is the linguistic correlate to the doctrine of categories or ways of being. We must now consider it as it bears upon the problem of nonbeing. Aristotle claims that we determine the essence of an individual thing by identifying its essential properties.