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) 1 have somewhat altered the concluding chapter, in consequence of an important criticism by Prof. v. Gizycki (Vierteljahrsschrift für Wissenschaftliche Philosophie, Jahr,. 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.