Logic is no doubt a science of “thought”; but “thought,” in that sense, is no more internal than it is external. Logic is the science of truth and falsity. But truth and falsity belong as much to propositions printed in books as to propositions in the human consciousness. The fact that a proposition is conscious or unconscious does not affect its truth or falsity.
But it may be said that logic is the theory of reasoning, and that reasoning can only be performed by a mind. That is certainly true, and must be true; for if anything could independently reason, it would be what we understand by a mind. But it does not follow that the phenomena that psychologists discover have any bearing upon the theory of reasoning. [—]
Logic includes a study of reasoning, it is true, and reasoning may be regarded,-not quite correctly, but we may waive that point, – as a psychical process. If we are to admit that, however, we must say that logic is not an all round study of reasoning, but only of the conditions of reasoning being bad or good, and if good to what degree, and in what application. Now good reasoning is reasoning which attains its purpose. Its purpose is to supply a guide for conduct, – and thinking, being an active operation, is a species of conduct, – in case no percept from which a judgment could have been directly formed, is at hand. Its object is to say what the reasoner either will think when that percept occurs, or what he would think if it did occur. The psychological process of reasoning is wholly aside from the purpose of logic.