As I review the course of my philosophical studies and attempt to express the conclusions to which they have led, I am conscious of special indebtedness to Aristotle, Spinoza, and Locke among the dead and to Santayana among the living. It is to them that I repeatedly turn both for refreshment and discipline. They represent, I may say, a selection or survival from the forces that have influenced me rather than a sequence which my own thinking has followed. I cannot name a date when they were first recognized as controlling. I know, however, that when I began teaching at Columbia University in I902 Aristotle, Spinoza, and Locke had already become the philosophers in whom I was most interested, and Santayana appeared to me as a brilliant and provoking writer. After reading his Life of Rrason, which I reviewed for the New York Nation, I felt that I had found in it a matchless commentary on our human thinking. Since the contributions to this volume of essays are admittedly personal and egotistic, I may as well say now that the Life of Reason is a book I wish I could have written myself. I do not ask Santayana to take this as a compliment, for it is a doubtful one. I make the confession to indicate that his book is the kind of book which appeals to me as genuinely philosophical. For as I understand the Life of ReaS01t, it makes no attempt to explain why the life of man should be intellectual. It attempts, rather, simply to tell the truth about that life. And telling the truth about the life of reason and trying to discover what that truth implies seem to me to be the business of philosophy. I had reached this conviction before I read the Life of Reason, but after reading it the conviction had received a force and an illumination which it had not had before.