This study examined psychoanalytic, physiological, and social learning models of depression in terms of etiology and symptomatology. Emphasis was placed on social learning theories of depression. First, Beck's cognitive approach stated that the root of depression was a negative cognitive set. Depressive episodes might be externally precipitated, but it was the individual's perception and appraisal of the event that rendered it depression inducing. Secondly, Seligman's learned helplessness model explained reactive depression in terms of a belief in one's own helplessness. Specifically, Seligman stated belief in the uncontrollability of outcomes resulted in depression, irrespective of the correspondence of such beliefs to objective circumstances. Additionally, depression resulted from noncontingent aversive stimulation and noncontingent positive reinforcement. Thirdly, Lewinsohn's model was based on these assumptions: a low rate of response-contingent positive reinforcement which acted as an eliciting stimulus for depressive behaviors. This low rate of response-contingent positive reinforcement constituted an explanation for the low rate of behaviors observed in the depressive. Total amount of response—contingent positive reinforcement is a function of a number of events reinforcing for the individual, availability of reinforcement in the environment, and social skills of the individual that are necessary to elicit reinforcement.