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
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.