[186] Nor indeed is any one ignorant that scarcely anything whatever of existing things, if you consider it in itself and by itself, is accurately understood; but by comparing it with its opposite, then we arrive at a knowledge of its true nature. As for instance, we comprehend what is meant by little by placing it in juxta-position with what is great; we understand what dry is by comparing it with wet, cold by comparing it with heat, light by comparing it with heavy, black by contrasting it with white, weak by contrasting it with strong, and few by comparing it with many. In the same way also, in whatever is referred to virtue or to vice,