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_. PREFACE TO THE FIFTH EDITION Such criticisms of my Ethical opinions and reasonings as have come under my notice, since the publication of the fourth edition of this treatise, have chiefly related to my treatment of the question of Free Will in Book i. chap. v., or to the hedonistic view of Ultimate Good, maintained in Book iii. chap. iv. I have accordingly rewritten certain parts of these two chapters, in the hope of making my arguments more clear and convincing: in each case a slight change in view will be apparent to a careful reader who compares the present with the preceding edition: but in neither case does the change affect the main substance of the argument. Alterations, in one or two cases not inconsiderable, have been made in several other chapters, especially Book i. chap. ii., and Book iii. chaps. i. and ii.: but they have chiefly aimed at removing defects of exposition, and do not (I think) in any case imply any material change of view. My thanks are again due to Miss Jones, of Girton College, for reading through the proofs of this edition and making most useful corrections and suggestions: as well as for revising the index which she kindly made for the fourth edition. PREFACE TO THE SIXTH EDITION