It is natural, then, to ask the question, why ratiocination should be an exception to a general law which attaches to the intellectual exercises of the mind; why it is held to be commensurate with logical science; and why logic is made an instrumental art sufficient for determining every sort of truth, while no one would dream of making any one formula, however generalized, a working rule at once for poetry, the art of medicine, and political warfare? This is what I have to remark concerning the Illative Sense, and in explanation of its nature and claims; and on the whole, I have spoken of it in four respects,—as viewed in itself, in its subject-matter, in the process it uses, and in its function and scope. First, viewed in its exercise, it is one and the same in all concrete matters, though employed in them in different measures. We do not reason in one way in chemistry or law, in another in morals or religion; but in reasoning on any subject whatever, which is concrete, we proceed, as far indeed as we can, by the logic of language, but we are obliged to supplement it by the more subtle and elastic logic of thought; for forms by themselves prove nothing. Secondly, it is in fact attached to definite subject-matters, so that a given individual may possess it in one department of thought, for instance, history, and not in another, for instance, philosophy. Thirdly, in coming to its conclusion, it proceeds always in the same way, by a method of reasoning, which is the elementary principle of that mathematical calculus of modern times, which has so wonderfully extended the limits of abstract science. Fourthly, in no class of concrete reasonings, whether in experimental science, historical research, or theology, is there any ultimate test of truth and error in our inferences besides the trustworthiness of the Illative Sense that gives them its sanction; just as there is no sufficient test of poetical excellence, heroic action, or gentleman-like conduct, other than the particular mental sense, be it genius, taste, sense of propriety, or the moral sense, to which those subject-matters are severally committed. Our duty in each of these is to strengthen and perfect the special faculty which is its living rule, and in every case as it comes to do our best. And such also is our duty and our necessity, as regards the Illative Sense. § 3. The Range of the Illative Sense.