A theory that emotional and allied diseases are due to a psychic injury or trauma, generally of a sexual nature, which did not produce an adequate reaction when it occurred and therefore remains as a subconscious or ‘affect’ memory to trouble the patient's mind. As an extension of this theory, Freudian treatment consists of encouraging the patient to tell everything that is associated with trains of thought which lead up to this memory. This achieves a ‘purging’ from the mind of the original ‘affect memory’ which is the cause of the symptoms. This form of treatment is also called psychocatharsis or abreaction.

The general term psychoanalysis is applied, in the first place, to the method of helping the patient to recover buried memories by free association of thoughts. In the second place, the term is applied to the body of psychological knowledge and theory accumulated and devised by Sigmund Freud (1856–1939) and his followers.