A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. I
John Stuart Mill · en
it is unanswerably urged by the adversaries of the syllogistic theory,
that the proposition, Socrates is mortal, is presupposed in the more
general assumption, All men are mortal: that we cannot be assured of the
mortality of all men, unless we are already certain of the mortality of
every individual man: that if it be still doubtful whether Socrates, or
any other individual we choose to name, be mortal or not, the same
degree of uncertainty must hang over the assertion, All men are mortal:
that the general principle, instead of being given as evidence of the
particular case, cannot itself be taken for true without exception,
until every shadow of doubt which could affect any case comprised with
it, is dispelled by evidence _aliundè_; and then what remains for the
syllogism to prove? That, in short, no reasoning from generals to
particulars can, as such, prove anything: since from a general principle
we cannot infer any particulars, but those which the principle itself
assumes as known.
This doctrine appears to me irrefragable; and if logicians, though
unable to dispute it, have usually exhibited a strong disposition to
explain it away, this was not because they could discover any flaw in
the argument itself, but because the contrary opinion seemed to rest on
arguments equally indisputable. In the syllogism last referred to, for
example, or in any of those which we previously constructed, is it not
evident that the conclusion may, to the person to whom the syllogism is
presented, be actually and _bonâ fide_ a new truth? Is it not matter of
daily experience that truths previously unthought of, facts which have
not been, and cannot be, directly observed, are arrived at by way of
general reasoning? We believe that the Duke of Wellington is mortal. We
do not know this by direct observation, so long as he is not yet dead.
If we were asked how, this being the case, we know the duke to be
mortal, we should probably answer, Because all men are so. Here,
therefore, we arrive at the knowledge of a truth not (as yet)
susceptible of observation, by a reasoning which admits of being
exhibited in the following syllogism:--
All men are mortal,
The Duke of Wellington is a man,
therefore
The Duke of Wellington is mortal.