An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

138
MEDIATE INFERENCE
and ask, not (as before) which of them yield valid con
clusions about S, but which of them yield valid conclusions
about P? This involves making the old major premise
into a new minor, and vice versa, so that the middle term
becomes predicate of the major premise and subject of the
minor. Testing the new moods by the rules, as before,
we find that five of them lead to valid conclusions, namely,
those which have been indicated above as belonging to
the "fourth
figure." The student should verify this result.
in the second and
The same process may be gone through
third figures ; but it will be found that no new -moods are
thus obtained.
6. Aristotle held that there is one canon or rule to
which all true reasoning conforms, either directly and
visibly in its very expression, or, if not, in such a way that
it can be expressed in direct conformity with the rule.
The canon is a concise statement of what mediate
inference or syllogism really is.
Syllogistic inference is
the application of a general principle (affirmative or
negative) to some particular case or cases or to a whole
class of cases. In the syllogism which expresses the
true nature of reasoning, the general principle is the
major premise ; the assertion that something
falls under
it is the minor premise. Such a syllogism shows the
rule of reasoning by the way in which it must naturally
be expressed, and hence was called by Aristotle a
perfect syllogism. In a perfect syllogism, the major
premise must be universal (affirmative or negative), for
it states the general principle which is to be applied,
and therefore it naturally comes first ; the minor
premise must be affirmative (and may be universal),
for it states that a given case comes under this principle.
Hence all the syllogisms of the first figure, and no
others, are perfect; for they alone conform to the
special
rules :