, differing only in the fact that they are in
inverse order, and this correspondence reveals the operation of one and
the same law. An inductive series is only a deductive series read
backward. Any two terms in a series whether inductive or deductive,
differ only in the degree of generality, and differ similarly from a
third term, so that two being known the third can be therefrom
determined. In a deductive series the terms differ by a constant
increase in the number of individualizing attributes--a concept being
expanded into a deductive series by such regular additions. Having two
terms we can proceed to the third--that is, from two propositions
expressing this relation, we can proceed to a conclusion. In an
inductive series the terms differ by a constant diminution in the number
of individualizing attributes--an individual term being expanded into an
inductive series, by successively dropping the attributes which compose
the individual term, until we reach the required degree of
generalization.

Thought must proceed in one of these two directions. The object-matter
of thought being composed wholly of attributes can differ only in the
presence or absence of certain attributes. A combination, then, of these
two movements must complete the intellectual orbit. The direction of the
movement of the mind will be determined by the end proposed. When we
possess the knowledge of phenomena and wish to discover law--that is,
when we seek information--we proceed by induction, from the individual
to the general. When possessed of knowledge, we wish to discover its
applications, when knowing the law, we wish to determine the phenomena
necessarily resulting therefrom, we proceed by deduction--from the
general to the individual. Complete knowledge, then, consists in the
highest possible generalization, and the expansion of this term into a
series, ending only with the last possible individualization. The aim of
physical science is to determine that half of the intellectual orbit
which lies between the individual and the general--the aim of
metaphysical science is to trace the other half which lies between the
general and the individual. When we seek to know what is, we proceed by
induction--the method of the phenomenal. When, knowing what is, we
proceed to determine what hence must be, we proceed by deduction--the
method of the Necessary. Thus Science, at first seeking principles,
proceeds by induction to establish them; but after th