Since some people think that the differentia, too, is a predicate of the various species in what it is, you should distinguish the genus from the differentia by employing the aforesaid elementary principles first, that the genus has a wider denotation than the differentia; then, that in giving what a thing is it is more fitting to state the genus than the differentia, for anyone who says that man is an animal shows what man is better than he who describes him as terrestrial