THE present volume consists mainly of articles which have appeared in Mind. I have added a paper first printed in the Philosophical Review, and there are also some essays which have not before been published. With three exceptions the whole belongs to the last five or six years. The parts of this work have been called chapters mainly for convenience in reference, but also because most of them represent more or less the chapters of a book-which I once intended to write. The title indicates, I think, the principal subject and aim of the contents. I am not offering a formal treatise on the nature and criterion of knowledge, truth, and reality, and yet this main-problem recurs and in some form is perhaps present throughout. The imperfection and incompleteness, too evident to the reader, may, I hope, be forgiven if these pages serve to emphasize the need and possibly even to stimulate the pursuit of the above inquiry. There has seldom, I imagine, been a time when the general question as to the criterion was more pressing, or when the answer, attained or attempted, promised better results. But I have myself little to contribute here beyond that which I have urged in former years. For the inner connection which, I hope, unites the various parts of this volume, I would refer to the remarks appended to the closing chapter.