A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. I
John Stuart Mill · en
The conclusion in an induction is inferred from the evidence itself, and
not from a recognition of the sufficiency of the evidence; as I infer
that my friend is walking towards me because I see him, and not because
I recognise that my eyes are open, and that eyesight is a means of
knowledge. In all operations which require care, it is good to assure
ourselves that the process has been performed accurately; but the
testing of the process is not the process itself; and, besides, may have
been omitted altogether, and yet the process be correct. It is precisely
because that operation is omitted in ordinary unscientific reasoning,
that there is anything gained in certainty by throwing reasoning into
the syllogistic form. To make sure, as far as possible, that it shall
not be omitted, we make the testing operation a part of the reasoning
process itself. We insist that the inference from particulars to
particulars shall pass through a general proposition. But this is a
security for good reasoning, not a condition of all reasoning; and in
some cases not even a security. Our most familiar inferences are all
made before we learn the use of general propositions; and a person of
untutored sagacity will skilfully apply his acquired experience to
adjacent cases, though he would bungle grievously in fixing the limits
of the appropriate general theorem. But though he may conclude rightly,
he never, properly speaking, knows whether he has done so or not; he has
not tested his reasoning. Now, this is precisely what forms of reasoning
do for us. We do not need them to enable us to reason, but to enable us
to know whether we reason correctly.
In still further answer to the objection, it may be added that, even
when the test has been applied, and the sufficiency of the evidence
recognised,--if it is sufficient to support the general proposition, it
is sufficient also to support an inference from particulars to
particulars without passing through the general proposition. The
inquirer who has logically satisfied himself that the conditions of
legitimate induction were realized in the cases A, B, C, would be as
much justified in concluding directly to the Duke of Wellington as in
concluding to all men. The general conclusion is never legitimate,
unless the particular one would be so too; and in no sense, intelligible
to me, can the particular conclusion be said to be drawn from the
general one. Whenever there is ground for drawing any conclusion at all
from particular instances, there is ground for a general conclusion; but
that this general conclusion should be actually drawn, however useful,
cannot be an indispensable condition of the validity of the inference in
the particular case. A man gives away sixpence by the same power by
which he disposes of his whole fortune; but it is not necessary to the
legality of the smaller act, that he should make a formal assertion of
his right to the greater one.