DEDUCTION (de ducere, to
draw from), drawing a particular truth from a general, antecedently
known, as distinguished from Induction, rising from particular
truths to a general. The syllogism is the
form of deduction. "An enunciation in which, from the
truth of certain assertions, the truth of another assertion
different from the first is inferred" (Aristotle, Prior
Analyt., bk. I, ch. I.).
The principle of deduction is, that things which agree with
the same thing agree with one another. The principle of induction
is, that in the same circumstances, and in the same substances, from the
same causes the same effects will follow.
The mathematical and metaphysical sciences are founded on deduction; the
physical sciences with empirical Psychology rest on induction.
Mill holds that all reasoning is ultimately inductive. For his views as to the
relation of induction and deduction, the nature of the syllogism and
mathematical inference, see Logic, bk. II. See also Whewell, Phil. of Induct.
Sci. For the Kantian use of the term, see next article.