3

When one thing is predicated of another, all that which is predicable of the predicate will be predicable also of the subject. Thus, "man" is predicated of the individual man; but "animal" is predicated of "man"; it will, therefore, be predicable of the individual man also: for the individual man is both "man" and "animal".

If genera are different and co-ordinate, their differentiae are themselves different in kind. Take as an instance the genus "animal" and the genus "knowledge". "With feet", "two-footed", "winged", "aquatic", are differentiae of "animal"; the species of knowledge are not distinguished by the same differentiae. One species of knowledge does not differ from another in being "two-footed".

But where one genus is subordinate to another, there is nothing to prevent their having the same differentiae: for the greater class is predicated of the lesser, so that all the differentiae of the predicate will be differentiae also of the subject.