nd no middle term, and therefore there is no
proof. Or if we write--

All authors are vain;
Cicero is an author:
.'. Cicero is a statesman--

here the term 'statesman' occurs without any voucher; it appears in the
inference but not in the evidence, and therefore violates the maxim of
all formal proof, 'not to go beyond the evidence.' It is true that if
any one argued--

All authors are vain;
Cicero wrote on philosophy:
.'. Cicero is vain--

this could not be called a bad argument or a material fallacy; but it
would be a needless departure from the form of expression in which the
connection between the evidence and the inference is most easily seen.

Still, a mere adherence to the same form of words in the expression of
terms is not enough: we must also attend to their meaning. For if the
same word be used ambiguously (as 'author' now for 'father' and anon for
'man of letters'), it becomes as to its meaning two terms; so that we
have four in all. Then, if the ambiguous term be the Middle, no
connection is shown between the other two; if either of the others be
ambiguous, something seems to be inferred which has never been really
given in evidence.

The above two Canons are, indeed, involved in the definition of a
categorical syllogism, which may be thus stated: A Categorical Syllogism
is a form of proof or reasoning (way of giving reasons) in which one
categorical proposition is established by comparing two others that
contain together only three terms, or that have one and only one term in
common.

The proposition established, derived, or inferred, is called the
Conclusion: the evidentiary propositions by which it is proved are
called the Premises.

The term common to the premises, by means of which the other terms are
compared, is called the Middle Term; the subject of the conclusion is
called the Minor Term; the predicate of the conclusion, the Major Term.

The premise in which the minor term occurs is called the Minor Premise;
that in which the major term occurs is called the Major Premise. And a
Syllogism is usually written thus:

Major Premise--All authors (Middle) are vain (Major);

Minor Premise--Cicero (Minor) is an author (Middle):

Conclusion--.'. Cicero (Minor) is vain (Major).

Here we have three propositions with three terms, each term occurring
twice. The minor and major terms are so called, because, when the
conclusion is an universal affirmative (which o