A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. I
John Stuart Mill · en
§ 3. Having noticed, in order to exclude from the province of Reasoning
or Inference properly so called, the cases in which the progression from
one truth to another is only apparent, the logical consequent being a
mere repetition of the logical antecedent; we now pass to those which
are cases of inference in the proper acceptation of the term, those in
which we set out from known truths, to arrive at others really distinct
from them.
Reasoning, in the extended sense in which I use the term, and in which
it is synonymous with Inference, is popularly said to be of two kinds:
reasoning from particulars to generals, and reasoning from generals to
particulars; the former being called Induction, the latter Ratiocination
or Syllogism. It will presently be shown that there is a third species
of reasoning, which falls under neither of these descriptions, and
which, nevertheless, is not only valid, but is the foundation of both
the others.
It is necessary to observe, that the expressions, reasoning from
particulars to generals, and reasoning from generals to particulars, are
recommended by brevity rather than by precision, and do not adequately
mark, without the aid of a commentary, the distinction between Induction
(in the sense now adverted to) and Ratiocination. The meaning intended
by these expressions is, that Induction is inferring a proposition from
propositions _less general_ than itself, and Ratiocination is inferring
a proposition from propositions _equally_ or _more_ general. When, from
the observation of a number of individual instances, we ascend to a
general proposition, or when, by combining a number of general
propositions, we conclude from them another proposition still more
general, the process, which is substantially the same in both instances,
is called Induction. When from a general proposition, not alone (for
from a single proposition nothing can be concluded which is not involved
in the terms), but by combining it with other propositions, we infer a
proposition of the same degree of generality with itself, or a less
general proposition, or a proposition merely individual, the process is
Ratiocination. When, in short, the conclusion is more general than the
largest of the premises, the argument is commonly called Induction; when
less general, or equally general, it is Ratiocination.