The Categories

Part 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.