Biological models postulate that psychosis stems from a genetic vulnerability that is expressed in structural or biochemical alterations of the central nervous system. According to psychological models the symptoms are the expression of a psychic dynamic whose origins can be traced back to the patient’s current or childhood relationships. Psychoanalytic theory itself stems from in-depth study of a small number of individual clinical cases which allowed the development of general theories of mental functioning. In the analytic theory of the psychotic state, explanatory models based on continuity and on discontinuity exist side by side. Karl Abraham was the first psychoanalyst after Freud to shed light on the genesis of psychotic disorders. Melanie Klein shared Sigmund Freud’s view concerning the fixation of psychosis at the point of transition from autoerotism to object love. Heinz Hartmann held that vulnerability to psychosis was due mainly to the difficulty experienced by the ego in mediating between the drives and reality.