The energy concept in psychiatry and psychodynamics has been emphasized again and again by many authors. In this concept an interplay of forces has been postulated to occur at a psychological level. The terms psychic energy and libido have frequently been used in psychiatry to emphasize this energy hypothesis. The "economy principle," as defined by Freud, has concerned itself with cathexis, i. e., the investment of energy in a particular situation or object. The control of libidinous energy by the various defensive mechanisms was described as countercathexis. In later psychiatric and psychologic theory the concepts of motivation, drive, and need are closely related to hypotheses of energy relationships; and from this it is presumed that the drive, need, or motivation sets into action certain central energizing processes directed toward a particular expressive goal. However, the operational definitions of these concepts have been limited to patterns of overt behavior, and the