The first section--an historical account of ancient theories of Universals--has already seen the light.[2] It brings together, as nowhere else, all the chief references to the doctrine of Realism in Plato, and exhibits the directly antagonistic position taken up by Aristotle towards his master. This it does so impressively that there could be no question of excluding it, even although it reproduces in part some of the matter of Chapter III., on the Categories. Being composed, in 1867, later than this Chapter, it is on that account written with all the firmer a grasp. On finishing it as it stands, Mr. Grote, in a private letter, expressed himself in terms that deserve to be quoted:--"I never saw before so clearly the extreme importance of Aristotle's speculations as the guides and stimulants of mediæval philosophy. If I had time to carry the account further, I should have been able to show how much the improved views of the question of Universals depended on the fact that more and more of the works of Aristotle, and better texts, became known to Albertus Magnus, Thomas Aquinas, and their successors. During the centuries immediately succeeding Boëthius, nothing of Aristotle except the Categories and the treatise De Interpretatione was known, and these in a Latin translation. Most fortunately the Categories was never put out of sight; and it is there that the doctrine of _Substantia Prima_ stands clearly proclaimed." [Footnote 2: In the Appendix to the senior editor's 'Manual of Mental and Moral Science' (1867).] The second section, or, rather, the part therein treating of Aristotle's doctrine of First Principles, is also a reprint. It was composed (in 1867) at the same time as the section on Universals, and was printed along with that; shorn, however, of the critical examination of Sir William Hamilton's views on Aristotle, which is now prefixed to the statement of the Aristotelian doctrine. Hamilton having (in Note A, appended to his edition of Reid's Works) claimed Aristotle as a supporter of the Philosophy of Common Sense, basing upon a long list of passages quoted, these were subjected by Mr. Grote to a searching criticism, the pointed vigour of which will be duly appreciated. The statement of his own view of Aristotle's doctrine, though containing little that may not be found at more places than one in the body of the present work, is yet reprinted, because iteration was his favourite art for impressing anything to which he attached as much importance as he did attach to this conviction of his, regarding the very heart of Aristotle's thought.