In this paper we define depression and postulate three forms of its pathology. The definition leans heavily upon the understanding of hope, which Lewin4and French3have suggested. It also derives from and leads back to laboratory experiments concerned with small-group behavior. In effect, this paper asserts a conceptual model of depressions whose primary purpose is to make feasible the experimental production of depression, its equivalents or its various components. The current analysis began when my colleagues and I observed some unintended results of an experiment concerned with the initiation of cooperation.6Two events appeared which seemed as important as the intended outcome. First, although we openly explained the experiment to all subjects, both during and after the trials, a large number of those who failed the task later reported that they had experienced intense depression subsequent to their failure, which remained for several days. Second, although