The authors analyzed traditional (categorical) and current (dimensional) approaches to the systematics of depressive disorders. Clinical concepts underlying current classifications of depression, including the positive-negative affect model, a dimensional rhythmological model of depression, are considered in details. Clinical differentiation of "intermediate" forms between categorically defined affective disorders (schizoaffective disorder - psychotic depression); a search for clinical and social predictors for depression adjusted for the affinity to the presentation of positive-negative affectivity; specification of the structure of constitutional abnormalities associated with affective pathology are key areas that demand further study.