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 toward me because I see him, and not because I
recognize 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 any thing 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
skillfully 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
recognized—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, can not 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.