Of the Understanding," and "Book II. Of the Passions." It has been generally and justly remarked, that the Treatise is among the least systematic of philosophical works--that it has neither a definite and comprehensive plan, nor a logical arrangement. It was, indeed, so utterly deficient in the former--there was so complete a want of any projected scope of subject which the author was bound to exhaust in what he wrote--that an attempt to divide and subdivide the matter after it had been written, according to a logical arrangement, would only, as a sort of _experimentum crucis_, have exposed the imperfect character of the original plan. The author, therefore, very discreetly allowed his matter to be arranged as the subjects of which he treated had respectively suggested themselves, and bestowed on his work a title rather general than comprehensive,--a title, of which all that can be said of its aptness to the subject is, that no part of his book can be said to be wholly without it, while he might have included an almost incalculable multitude of other subjects within it. He called it simply "A Treatise of Human Nature;" and by a subsidiary title, explanatory rather of his method than definitive of his matter, he called it "an attempt to introduce the experimental method of reasoning into moral subjects." The purely metaphysical,[67:1] and, at the same time, the most original portion of the work, and that which has most conspicuously rendered itself a constituent part of the literature of intellectual philosophy, is "Book I. Of the Understanding." "Book II. Of the Passions," contains mixed metaphysics and ethics, with occasional notices of phenomena, which, though Hume does not, other writers would be likely to connect with physiological inquiries. The third book, "Of Virtue and Vice in General," published a year later, is of an ethical character, being an inquiry into the origin and proper system of morals, and an application of the system to government and politics.