(a) Whately, a well-known Nominalist, regarded Logic as the Science and Art of Reasoning, but at the same time as “entirely conversant about language”; that is to say, it is the business of Logic to discover those modes of statement which shall ensure the cogency of an argument, no matter what may be the subject under discussion.  Thus, All fish are cold-blooded, .’. some cold-blooded things are fish: this is a sound inference by the mere manner of expression; and equally sound is the inference, All fish are warm-blooded, .’. some warm-blooded things are fish.  The latter proposition may be false, but it follows; and (according to this doctrine) Logic is only concerned with the consistent use of words:  the truth or falsity of the proposition itself is a question for Zoology.  The short-coming of extreme Nominalism lies in speaking of language as if its meaning were unimportant.  But Whately did not intend this:  he was a man of great penetration and common-sense.

(b) Hamilton, our best-known Conceptualist, defined Logic as the science of the “formal laws of thought,” and “of thought as thought,” that is, without regard to the matter thought about.  Just as Whately regarded Logic as concerned merely with cogent forms of statement, so Hamilton treated it as concerned merely with the necessary relations of thought.  This doctrine is called Conceptualism, because the simplest element of thought is the Concept; that is, an 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