THIS book is an essay in the speculative treatment of certain problems, suggested but not usually discussed in the course of a thorough empirical study of mental phenomena. Inasmuch as these problems all relate to the real nature and actual performances and relations of the human mind, the essay nay properly be called metaphysical. Let it be confessed, then, that the author comes forward with a treatise in metaphysics, - in the more special meaning of that term. I think, however, that in spite of the marked disfavor into which all metaphysics has fallen in certain quarters, no detailed apology for asking readers for such a treatise need be offered in its Preface. Indeed, the first two chapters of the book are occupied in showing how inevitable is the demand which the science of psychology makes for a further philosophical discussion of all its principal problems. If, then, this demand is not made perfectly clear hy the more detailed discussion which follows, it would be quite use-less to put it forward unsupported, at the beginning of my task, in the hope of producing a favorable first impression upon reluctant intelligences. "No one whose peace of mind is sure to be disturbed by any attempt, however carried out, at this form of reflective thinking should venture beyond the titlepa-ge and table of contents of this volume. On the other hand, however, I wish to be held res-ponsible for two things which are required in order to entitle to respect every tre-atise of a similar character. These are, first, the statement of the facts and laws, scientifically established, to which the speculative discussion constantly refers for it own grounds in experience. And for metaphysics which has no foundations in incontestable experience, I have as little respect as has any one. But besides this constant appeal to facts and to laws empirically established, sound reasoning is indispensable for the derivation of acceptable conclusions in any metaphysical enterprise. Any reader, or critic, therefore, who will point out violations of either of these two requirements, will be entitled to grateful recognition for his service, no less by the author than by the readers of this volume. A few words concerning the relations which this book sustains to preceding works by the same author will be helpful for its better understanding. In some sort the entire volüme may be regarded as in continuation of a series of works I on psychology, or the Science of mental phenomena. This science, which, as a science, is, and ever must remain, chiefly descriptive, starts many inquiries regar-ding the real natüre and relations to the external World.."