Ratiocination, thus restricted and put into grooves, is what I have called Inference, and the science, which is its regulating principle, is Logic. The first step in the inferential method is to throw the question to be decided into the form of a proposition; then to throw the proof itself into propositions, the force of the proof lying in the comparison of these propositions with each other. When the analysis is carried out fully and put into form, it becomes the Aristotelic syllogism. However, an inference need not be expressed thus technically; an enthymeme fulfils the requirements of what I have called Inference. So does any other form of words with the mere grammatical expressions, “for,” “therefore,” “supposing,” “so that,” “similarly,” and the like. Verbal reasoning, of whatever kind, as opposed to mental, is what I mean by inference, which differs from logic only inasmuch as logic is its scientific form. And it will be more convenient here to use the two words indiscriminately, for I shall say nothing about logic which does not in its substance also apply to inference. Logical inference, then, being such, and its office such as I have described, the question follows, how far it answers the purpose for which it is used. It proposes to provide both a test and a common measure of reasoning; and I think it will be found partly to succeed and partly to fail; succeeding so far as words can in fact be found for representing the countless varieties and subtleties of human thought, failing on account of the fallacy of the original assumption, that whatever can be thought can be adequately expressed in words.