future, according to the divisions of time.
An affirmation is a positive assertion of something about something,
a denial a negative assertion.
Now it is possible both to affirm and to deny the presence of
something which is present or of something which is not, and since
these same affirmations and denials are possible with reference to
those times which lie outside the present, it would be possible to
contradict any affirmation or denial. Thus it is plain that every
affirmation has an opposite denial, and similarly every denial an
We will call such a pair of propositions a pair of
contradictories. Those positive and negative propositions are said
to be contradictory which have the same subject and predicate. The
identity of subject and of predicate must not be 'equivocal'. Indeed
there are definitive qualifications besides this, which we make to
meet the casuistries of sophists.
Some things are universal, others individual. By the term
'universal' I mean that which is of such a nature as to be
predicated of many subjects, by 'individual' that which is not thus
predicated. Thus 'man' is a universal, 'Callias' an individual.
Our propositions necessarily sometimes concern a universal
subject, sometimes an individual.
If, then, a man states a positive and a negative proposition of
universal character with regard to a universal, these two propositions
are 'contrary'. By the expression 'a proposition of universal
character with regard to a universal', such propositions as 'every man