The aim of psychoanalysis is the undoing of repression and other defences, the recovery of lost memories, and the achievement of insight or a fresh understanding of previously puzzling behaviour. Psychoanalytic psychotherapy is practised much more widely than psychoanalysis, from which it has evolved. Sigmund Freud’s first major psychoanalytic proposal concerned the nature of hysteria. This is a condition in which the patient experiences physical symptoms, for example blindness or paralysis, without obvious organic cause. Although in principle the practice of psychoanalysis requires lengthy specialist training, including the psychoanalysis of the trainee analyst, many clinical psychologists, as well as psychiatrists and social workers, practise psychotherapy guided by psychoanalytic principles without receiving a full psychoanalytic training. Efforts have been made to demonstrate the scientific validity of psychoanalysis by replicating in the laboratory clinical phenomena such as projection, repression, and dream symbolism.