Lately more and more voices are heard proclaiming that the problem of general psychology is a problem of the first order. What is most remarkable is that this opinion does not come from philosophers who have made generalization their professional habit, nor even from theoretical psychologists, but from the psychological practitioners who elaborate the special areas of applied psychology: psychiatrists and industrial psychologists, the representatives of the most exact and concrete part of our science. The various psychological disciplines have obviously reached a turning point in the development of their investigations, the gathering of factual material, the systematization of knowledge, and the statement of basic positions and laws. Further advance along a straight line, the simple continuation of the same work, the gradual accumulation of material, are proving fruitless or even impossible. In order to go further we must choose a path.