Considering depression as basically an ego response to stress, Benton defines the sources of the depressive mood. The first is the impact upon the ego of an external stress in the person's life, which exerts a 'primary depressive impact'. The second (as in manic-depressive illness) is a source other than stress, such as constitutional and metabolic factors. The third is the 'release' of depressive complexes which are formed early in life at points of narcissistic injury. This is a release form of depression in contrast with the induced form, as in the first example. Such a classification offers some structure for research on the precipitants of depression, but the entire concept does not appear to offer clarification of depressive mechanisms beyond those understood psychoanalytically. There is no consideration of drives, particularly aggression, in relation to depression in these formulations.