A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. I
John Stuart Mill · en
§ 6. To complete the series of considerations connected with the
philosophical character of the syllogism, it is requisite to consider,
since the syllogism is not the universal type of the reasoning process,
what is the real type. This resolves itself into the question, what is
the nature of the minor premise, and in what manner it contributes to
establish the conclusion: for as to the major, we now fully understand,
that the place which it nominally occupies in our reasonings, properly
belongs to the individual facts or observations of which it expresses
the general result; the major itself being no real part of the argument,
but an intermediate halting-place for the mind, interposed by an
artifice of language between the real premises and the conclusion, by
way of a security, which it is in a most material degree, for the
correctness of the process. The minor, however, being an indispensable
part of the syllogistic expression of an argument, without doubt either
is, or corresponds to, an equally indispensable part of the argument
itself, and we have only to inquire what part.
It is perhaps worth while to notice here a speculation of a philosopher
to whom mental science is much indebted, but who, though a very
penetrating, was a very hasty thinker, and whose want of due
circumspection rendered him fully as remarkable for what he did not see,
as for what he saw. I allude to Dr. Thomas Brown, whose theory of
ratiocination is peculiar. He saw the _petitio principii_ which is
inherent in every syllogism, if we consider the major to be itself the
evidence by which the conclusion is proved, instead of being, what in
fact it is, an assertion of the existence of evidence sufficient to
prove any conclusion of a given description. Seeing this, Dr. Brown not
only failed to see the immense advantage, in point of security for
correctness, which is gained by interposing this step between the real
evidence and the conclusion; but he thought it incumbent on him to
strike out the major altogether from the reasoning process, without
substituting anything else, and maintained that our reasonings consist
only of the minor premise and the conclusion, Socrates is a man,
therefore Socrates is mortal: thus actually suppressing, as an
unnecessary step in the argument, the appeal to former experience. The
absurdity of this was disguised from him by the opinion he adopted, that
reasoning is merely analysing our own general notions, or abstract
ideas; and that the proposition, Socrates is mortal, is evolved from the
proposition, Socrates is a man, simply by recognising the notion of
mortality as already contained in the notion we form of a man.