If, then, a genus is suggested for something that is, first take a look at all objects which belong to the same genus as the thing mentioned, and see whether the genus suggested is not predicated of some of them, as in the case of accident: eg if good is laid down as the genus of pleasure, see whether some pleasure is not good; for, if so, clearly good is not the genus of pleasure; for the genus is predicated of all the members of the same species.