The subject matter of the history of philosophy consists of the efforts which individual thinkers have made to explain or perchance to solve the ultimate problems of knowledge and of being. Modern philosophy—i. e. the philosophy of the last three centuries—has been specially concerned with four great problems. These problems, moreover—as I have shown in my Philosophic Problems (Eng. Tr. 1905)—are intimately related to each other, and there likewise exists a most significant analogy between them, in that the antithesis of continuity and discontinuity is of fundamental importance in each of them, except that it manifests itself under different forms.
1. The psychological problem originates from the inquiry concerning the essential attributes of psychic life. Is the soul a distinct substance, or does its essential nature consist of a peculiar activity? Is the soul composed of a variety of independent elements, or is it characterized by unity and totality? The discussion of these questions can be of value only as it is based upon a detailed investigation of psychical phenomena and functions. It will likewise appear that the solution of these questions has a very important bearing on the treatment and the solution of the remaining philosophic problems.
Whilst psychological investigation finds its subject matter in the bare facts of psychic life, there are two