The chief alterations in this fourth edition are the following. (1) I have expanded the discussion on Free Will in Book i. chap. v. § 3, to meet the criticisms of Mr. Fowler, in his Principles of Morals, and Dr. Martineau, in his Types of Ethical Theory. (2) In consequence of the publication of the last-mentioned work, I have rewritten part of chap. xii. of Book iii., which deals with the Ethical view maintained by Dr. Martineau. (3) I have expanded the argument in Book iii. chap. xiv., to meet objections ably urged by Mr. Rashdall in Mind (April 1885). (4) I have somewhat altered the concluding chapter, in consequence of an important criticism by Prof. v. Gizycki (Vierteljahrsschrift fÜr Wissenschaftliche Philosophie, Jahrg. iv. Heft i.) which I had inadvertently overlooked in preparing the third edition. Several pages of new matter have thus been introduced: for which—I am glad to say—I have made room by shortening what seemed prolix, omitting what seemed superfluous, and relegating digressions to notes, in other parts of the work: so that the bulk of the whole is not increased.

For the index which forms a new feature in the present edition I am indebted to the kindness of Miss Jones of Girton College, the author of Elements of Logic as a Science of Propositions.