[NOTE: I have let this paper stand much as written, though now conscious that much more is crowded into it than could properly be presented in one paper. The drift of the ten years from ’99 to ’09 has made, I venture to believe, for increased clearness in the main positions of the paper: The revival of a naturalistic realism, the denial of the existence of “consciousness,” the development of functional and dynamic psychology (accompanied by aversion to interpretation of functions as faculties of a soul-substance)--all of these tendencies are sympathetic with the aim of the paper. There is another reason for letting it stand: the new functional and pragmatic empiricism proffered in this volume has been constantly objected to on the ground that its conceptions of knowledge and verification lead only to subjectivism and solipsism. The paper may indicate that the identification of experience with bare states of consciousness represents the standpoint of the critic, not of the empiricism criticised, and that it is for him, not for me, to fear the subjective implications of such a position. The paper also clearly raises the question as to how far the isolation of “consciousness” from nature and social life, which characterizes the procedure of many psychologists of to-day, is responsible for keeping alive quite unreal problems in philosophy.] THE SIGNIFICANCE OF THE PROBLEM OF KNOWLEDGE[63] It is now something over a century since Kant called upon philosophers to cease their discussion regarding the nature of the world and the principles of existence until they had arrived at some conclusion regarding the nature of the knowing process. But students of philosophy know that Kant formulated the question “how knowledge is possible” rather than created it. As matter of fact, reflective thought for two centuries before Kant had been principally interested in just this problem, although it had not generalized its own interest. Kant brought to consciousness the controlling motive. The discussion, both in Kant himself and in his successors, often seems scholastic, lost in useless subtlety, scholastic argument, and technical distinctions. Within the last decade in particular there have been signs of a growing weariness as to epistemology, and a tendency to turn away to more fertile fields. The interest shows signs of exhaustion.