Seeing, moreover, that of contraries, the one is sometimes named by the privation of the other, as (e.g.) inequality seems to be the privation of equality (for things that are not equal are called unequal), it is therefore clear that the contrary named by the privation must of necessity be defined through the other; whereas the other cannot then be defined through the one named by the privation; for else we should find that each was being made known by the other.