The models of depression hypothesized by leading cognitive-behavioral theorists—especially those of Beck, Lewinsohn, Rehm, and Seligman—are analyzed and it is shown that they probably explain how people make themselves appropriately sad, regretful, disappointed, and annoyed when they suffer major losses and inconveniences. These models, however, do not explain why many people with similar losses and inconveniences also make themselves inappropriately depressed and self-hating. It is hypothesized that the rational-emotive therapy (RET) model of depression has a crucial cognitive and philosophic element—the inclusion of absolutistic, dogmatic shoulds, oughts, and musts—that differentiates people's appropriate feelings of sadness from their inappropriate feelings of depression, and that therefore appreciably adds to our understanding of the causative factors in depression. This neglected theory of depression is examined and discussed.