The three books of the Treatise on Human Nature, which appeared in 1739-40, are entitled Of the Understanding, Of the Passions, Of Morals.  Of the five volumes of the Essays, the first contains the Essays Moral, Political, and Literary, 1741-42; the second, the Enquiry concerning Human Understanding, 1748; the third, the Enquiry concerning the Principles of Morals, 1751; the fourth, the Political Discourses, 1752; the fifth, 1757, the Four Dissertations, including that On the Passions and the Natural History of Religion.  After Hume’s death appeared the Autobiography, 1777; the Dialogues concerning Natural Religion, 1779; and the two small essays on Suicide and the Immortality of the Soul, 1783.[1] The Philosophical Works were published in 1827, and frequently afterward.[2]

[Footnote 1:  Or 1777, cf.  Green and Grose’s edition, vol. iii. p. 67 seq.—­Tr.]

[Footnote 2:  Among the works on Hume we may mention Jodl’s prize treatise, 1872, and Huxley’s Hume (English Men of Letters), 1879. [The reader may be referred also to Knight’s Hume (Blackwood’s Philosophical Classics), 1886; to T.H.  Green’s “Introductions” in Green and Grose’s edition of the collected works in four volumes, 1874 (new ed. 1889-90), which is now standard; and to Selby-Bigge’s reprint of the original edition of the Treatise, I vol., 1888, with a valuable Analytical Index.]]

Hume’s object, like that of Berkeley, is the improvement of Locke’s doctrine of knowledge.  In several respects he does not go so far as Berkeley, in others very much farther.  In agreement with Berkeley’s ultra-nominalism, which combats even the possibility of abstract ideas, he yet does not follow him to the extent of denying external reality.  On the other hand, he carries out more consistently Berkeley’s hint that immediate sensation includes less than is ascribed to it (e.g., that by vision we perceive colors only, and not distance, etc.), as well as his principle—­destructive to the certainty of our knowledge of nature—­that there is no causality among phenomena; and brings the question of substance to, the negative conclusion, that there is no need whatever for a support for groups of qualities, and, therefore, that substantiality is to be denied to immaterial as well as to material beings.  The points in Locke’s philosophy which seemed to Hume to need completion were different from those at which Berkeley had struck in.  The antithesis of rational and empirical knowledge is more sharply conceived; the combination of ideas is not left to the choice of the understanding but placed under the dominion of psychological laws; and to the distinction between outer and inner experience (to the former of which priority is conceded, on the ground that we must have had an external sensation before we can, through reflection, be conscious of it as an internal phenomenon), there is added a second, as important as the other and crossing it, between impressions and ideas, of which the former are likewise made prior to the latter.