'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.
Expressions which are in no way composite signify substance,
quantity, quality, relation, place, time, position, state, action,
or affection. To sketch my meaning roughly, examples of substance
are 'man' or 'the horse', of quantity, such terms as 'two cubits long'
or 'three cubits long', of quality, such attributes as 'white',
'grammatical'. 'Double', 'half', 'greater', fall under the category of
relation; 'in a the market place', 'in the Lyceum', under that of
place; 'yesterday', 'last year', under that of time. 'Lying',
'sitting', are terms indicating position, 'shod', 'armed', state;
'to lance', 'to cauterize', action; 'to be lanced', 'to be
No one of these terms, in and by itself, involves an affirmation; it
is by the combination of such terms that positive or negative
statements arise. For every assertion must, as is admitted, be
either true or false, whereas expressions which are not in any way
composite such as 'man', 'white', 'runs', 'wins', cannot be either
true or false.