A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. I
John Stuart Mill · en
And since a large portion of our knowledge is thus acquired, logicians
have persisted in representing the syllogism as a process of inference
or proof; though none of them has cleared up the difficulty which arises
from the inconsistency between that assertion, and the principle, that
if there be anything in the conclusion which was not already asserted in
the premises, the argument is vicious. For it is impossible to attach
any serious scientific value to such a mere salvo, as the distinction
drawn between being involved _by implication_ in the premises, and being
directly asserted in them. When Archbishop Whately says[7] that the
object of reasoning is "merely to expand and unfold the assertions wrapt
up, as it were, and implied in those with which we set out, and to bring
a person to perceive and acknowledge the full force of that which he
has admitted," he does not, I think, meet the real difficulty requiring
to be explained, namely, how it happens that a science, like geometry,
_can_ be all "wrapt up" in a few definitions and axioms. Nor does this
defence of the syllogism differ much from what its assailants urge
against it as an accusation, when they charge it with being of no use
except to those who seek to press the consequences of an admission into
which a person has been entrapped without having considered and
understood its full force. When you admitted the major premise, you
asserted the conclusion; but, says Archbishop Whately, you asserted it
by implication merely: this, however, can here only mean that you
asserted it unconsciously; that you did not know you were asserting it;
but, if so, the difficulty revives in this shape--Ought you not to have
known? Were you warranted in asserting the general proposition without
having satisfied yourself of the truth of everything which it fairly
includes? And if not, is not the syllogistic art _primâ facie_ what its
assailants affirm it to be, a contrivance for catching you in a trap,
and holding you fast in it?[8]
§ 3. From this difficulty there appears to be but one issue. The
proposition that the Duke of Wellington is mortal, is evidently an
inference; it is got at as a conclusion from something else; but do we,
in reality, conclude it from the proposition, All men are mortal? I
answer, no.
The error committed is, I conceive, that of overlooking the distinction
between two parts of the process of philosophizing, the inferring part,
and the registering part; and ascribing to the latter the functions of
the former. The mistake is that of referring a person to his own notes
for the origin of his knowledge. If a person is asked a question, and is
at the moment unable to answer it, he may refresh his memory by turning
to a memorandum which he carries about with him. But if he were asked,
how the fact came to his knowledge, he would scarcely answer, because it
was set down in his note-book: unless the book was written, like the
Koran, with a quill from the wing of the angel Gabriel.