Prior Analytics - Book II
opposites are never subjects of a single science, and contraries are
opposites, so that we get the first figure, or that the knowable and
the unknowable are not subjects of a single science: this proof is
in the third figure: for it is true of C (the knowable and the
unknowable) that they are contraries, and it is false that they are
the subjects of a single science.
Similarly if the premiss objected to is negative. For if a man
maintains that contraries are not subjects of a single science, we
reply either that all opposites or that certain contraries, e.g.
what is healthy and what is sickly, are subjects of the same
science: the former argument issues from the first, the latter from
the third figure.
In general if a man urges a universal objection he must frame his
contradiction with reference to the universal of the terms taken by
his opponent, e.g. if a man maintains that contraries are not subjects
of the same science, his opponent must reply that there is a single
science of all opposites. Thus we must have the first figure: for
the term which embraces the original subject becomes the middle term.
If the objection is particular, the objector must frame his
contradiction with reference to a term relatively to which the subject
of his opponent's premiss is universal, e.g. he will point out that
the knowable and the unknowable are not subjects of the same
science: 'contraries' is universal relatively to these. And we have
the third figure: for the particular term assumed is middle, e.g.
the knowable and the unknowable. Premisses from which it is possible
to draw the contrary conclusion are what we start from when we try
to make objections. Consequently we bring objections in these
figures only: for in them only are opposite syllogisms possible, since
the second figure cannot produce an affirmative conclusion.
Besides, an objection in the middle figure would require a fuller
argument, e.g. if it should not be granted that A belongs to B,
because C does not follow B. This can be made clear only by other