The concepts which are discussed in the following chapters have been developed and tried out in the course of the last ten years. They are based on both experimental investigations and case histories. In presenting them we are not promulgating a new "system" limited to a specific content, but rather we are describing a "tool," a set of concepts by means of which one can represent psychological reality. As I see it, the outstanding characteristics of this undertaking are:1. It tries to build up a framework for the constructive representation and derivation of psychological processes which is logically consistent and at the same time adapted to the special properties of the "psychological life space."2. It includes both the characteristics of the environment and of the person. 3. It makes no more assumptions than are required. 4. It proceeds by a method of successive approximation. The concepts developed in the following pages are "operational" in so far as a univocal relation between concepts and observable data is consistently maintained. Although the concepts always extend from the level of phenomena into the level of causal relationships, they are "descriptive" in the sense of Newton's dictum: Hypotheses non fingo. That is, they express the nature of certain relationships and at the same time avoid that type of "explanation" which is characteristic of speculative theories and which is at present, as it seems to me, a real handicap to our science.