In the chapters of this book, I have mainly limited myself to those issues on which I feel that I can express some positive and constructive opinions, because purely negative criticism seems inappropriate.For this reason, epistemology takes up somewhat more space in this book than metaphysics, and some topics, which have been much discussed by philosophers, are treated very briefly, if at all. I have been given invaluable help by the unpublished works of GE Moors and JM Keynes: the former in dealing with the relation of sense-data to material objects, the latter in matters of probability and inductive law.I have also benefited greatly from the critiques and suggestions of Professor Gilbert Murray.