m, which started
with Aristotle and has grown hoary with repetition, and so venerable
that it is one of the commonplaces of educated speech, runs as follows:
_All men are mortal, Socrates is a man, Therefore Socrates is mortal_.
Here there is the general principle, _All men are mortal_, and the
assertion about the particular case, _Socrates is a man_. The two have
one term in common, _men_ (or more strictly, the class Man), which is
known as the middle term, through which we reach the conclusion that the
characteristic of mortality in which all men are similar is true also of
Socrates, by virtue of his being a man. Of the other terms, _mortal_,
which is the more inclusive, is known as the major term, and _Socrates_,
the less inclusive, as the minor term. The first two propositions are
the premises, that which contains the major term being known as the
major premise, and the other as the minor premise.

The validity of the syllogism lies, as I have said, in the assertion of
a general principle, and the bringing of the particular case in hand
under that principle: if the principle is granted as incontrovertible,
and the special case as really coming under it, the conclusion is
inevitable.

On the syllogism in its various forms deductive logic has built up an
imposing structure of rules and conclusions. In practice the value of
the syllogism is largely indirect. The trouble with it in itself as a
mode of progress in reasoning is twofold: in the first place there are
very few general principles which, if you are cautious, you will accept
without reservations; and in the second place the crucial question in
another set of cases is whether the given case really falls under the
general principle. The syllogism, _All great statesmen are farsighted,
Daniel Webster was a great statesman, Therefore Daniel Webster was
farsighted_, sounds simple; but two generations have disagreed on the
question whether Webster was a great statesman; and both _great
statesman_ and _farsighted_ are such vague and inclusive terms that one
would either accept a general principle of which they are terms as a
harmless truism, or else balk at being asked to grant a proposition
which might have unexpected meanings thrust into it. This double
difficulty pursues the syllogism as a device for forwarding knowledge:
either it sets forth a truth so large and vague that you cannot say
whether you accept it for all cases or not, or else the disagreement
comes o