Prior Analytics - Book II
demonstrative syllogisms are formed by means of the aforesaid figures,
but also rhetorical syllogisms and in general any form of
persuasion, however it may be presented. For every belief comes either
through syllogism or from induction.
Now induction, or rather the syllogism which springs out of
induction, consists in establishing syllogistically a relation between
one extreme and the middle by means of the other extreme, e.g. if B is
the middle term between A and C, it consists in proving through C that
A belongs to B. For this is the manner in which we make inductions.
For example let A stand for long-lived, B for bileless, and C for
the particular long-lived animals, e.g. man, horse, mule. A then
belongs to the whole of C: for whatever is bileless is long-lived. But
B also ('not possessing bile') belongs to all C. If then C is
convertible with B, and the middle term is not wider in extension,
it is necessary that A should belong to B. For it has already been
proved that if two things belong to the same thing, and the extreme is
convertible with one of them, then the other predicate will belong
to the predicate that is converted. But we must apprehend C as made up
of all the particulars. For induction proceeds through an
enumeration of all the cases.
Such is the syllogism which establishes the first and immediate
premiss: for where there is a middle term the syllogism proceeds
through the middle term; when there is no middle term, through
induction. And in a way induction is opposed to syllogism: for the
latter proves the major term to belong to the third term by means of
the middle, the former proves the major to belong to the middle by
means of the third. In the order of nature, syllogism through the
middle term is prior and better known, but syllogism through induction
is clearer to us.