abstract idea, such as is signified
by the word _man, planet, colour, virtue_; not a representative or
generic image, but the thought of all attributes common to any class of
things. Men, planets, colours, virtuous actions or characters, have,
severally, something in common on account of which they bear these
general names; and the thought of what they have in common, as the
ground of these names, is a Concept. To affirm or deny one concept of
another, as _Some men are virtuous_, or _No man is perfectly virtuous_,
is to form a Judgment, corresponding to the Proposition of which the
other schools of Logic discourse. Conceptualism, then, investigates the
conditions of consistent judgment.

To distinguish Logic from Psychology is most important in connection
with Conceptualism. Concepts and Judgments being mental acts, or
products of mental activity, it is often thought that Logic must be a
department of Psychology. It is recognised of course, that Psychology
deals with much more than Logic does, with sensation, pleasure and pain,
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.

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