1. Biological theories a. Inherited. Numerous studies have been conducted that confirm the involvement of heredity in the development of a depressed state. The incidence is apparently significantly higher among relatives of individuals with this disorder than in the general population (DSM-III-R, 1987). b. Biochemical. Violations of electrolyte balance, apparently, play a role in the development of a depressive state. An error in metabolism leads to a transposition of sodium and potassium within the neuron (Gibbons, 1960). Another biochemical theory gives importance to biogenic amines – noradrenaline, dopamine and serotonin. Concentrations of these chemicals are inadequate in depressed individuals (Janowsky et al., 1988). Biochemical theories are contradictory. It is also necessary to establish whether depression is caused by biochemical changes or whether biochemical changes occur in response to the development of a depressive state. 2. Psychosocial theories a. Psychoanalytic. In this theory (Klein, 1934), importance is given to unsatisfactory relationships in early childhood between a mother and a child as a factor predisposing to the development of a depressive state. The baby’s needs remain unmet, which creates a condition that is seen as loss. The grief reaction does not find its solution, as a result of which rage and hostility turn on themselves. The “I” remains weak, while the “superego” strengthens and becomes punishing. b. Cognitive. Proponents of this theory (Beck et al., 1979) are convinced that a depressed state results from impaired cognition. Disturbed forms of thinking support the individual’s negative assessment of himself. Perceptions of their inconsistency and worthlessness prevail. Future prospects are pessimistic and hopeless. at. Theory of Learning. This theory (Seligman, 1973) suggests that the individual is predisposed to the development of a depressed state that he does not sufficiently control his life circumstances. It is believed that this belief arises from life experience leading to failure (imaginary or real). After numerous failures, the individual feels helpless in achieving his aspirations and therefore refuses any further attempts in this direction. This memorized helplessness is regarded as a predisposition to the development of a depressed state, d. Theory of the loss of an object. This theory (Bowlby, 1973) states that a depressive state occurs when a child is separated from loved ones during the first six months of his life or the latter refuse him. The process of forming bonds is disrupted, and the child moves away from people and the environment.