emotion, volition; but in the region of the intellect, especially in its
most deliberate and elaborate processes, namely, conception, judgment,
and reasoning, Logic and Psychology seem to occupy common ground. In
fact, however, the two sciences have little in common except a few
general terms, and even these they employ in different senses. It is
usual to point out that Psychology tries to explain the subjective
_processes_ of conception, judgment and reasoning, and to give their
natural history; but that Logic is wholly concerned with the _results_
of such processes, with concepts, judgments and reasonings, and merely
with the validity of the results, that is, with their truth or
consistency; whilst Psychology has nothing to do with their validity,
but only with their causes. Besides, the logical judgment (in Formal
Logic at least) is quite a different thing from the psychological: the
latter involves feeling and belief, whereas the former is merely a given
relation of concepts. _S is P_: that is a model logical judgment; there
can be no question of believing it; but it is logically valid if _M is
P_ and _S is M_. When, again, in Logic, one deals with belief, it
depends upon evidence; whereas, in Psychology belief is shown to depend
upon causes which may have evidentiary value or may not; for Psychology
explains quite impartially the growth of scientific insight and the
growth of prejudice.

(c) Mill, Bain, and Venn are the chief Materialist logicians; and to
guard against the error of confounding Materialism in Logic with the
ontological doctrine that nothing exists but Matter, it may suffice to
remember that in Metaphysics all these philosophers are Idealists.
Materialism in Logic consists in regarding propositions as affirming or
denying relations (_cf._ § 5) between matters-of-fact in the widest
sense; not only physical facts, but ideas, social and moral relations;
it consists, in short, in attending to the meaning of propositions. It