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.