Needs (Murray, 1938) and state-variables (Skinner, 1938).

Skinner's concept of drive as a state-variable and his powerful rationale for introducing it agree closely with Murray's treatment of need. Operant behaviorists' usual deprecation of motivation in favor of stimulus control arises partly from features of parameters, insufficiently explored in some regions, of Skinner box research. For human adults on rich reinforcement schedules, response selection is chiefly controlled by the regnant motive. Skinner's life-long interest in inner events and translating psychodynamic concepts into behaviorese was obscured by his metalanguage philosophy of science (behaviorism).