In founding psychoanalysis, Freud developed therapeutic techniques such as the use of free association and discovered transference, establishing its central role in the analytic process. Freud's redefinition of sexuality to include its infantile forms led him to formulate the Oedipus complex as the central tenet of psychoanalytical theory. His analysis of dreams as wish-fulfillments provided him with models for the clinical analysis of symptom formation and the underlying mechanisms of repression. On this basis Freud elaborated his theory of the unconscious and went on to develop a model of psychic structure comprising id, ego and super-ego. Freud postulated the existence of libido, a sexualised energy with which mental processes and structures are invested and which generates erotic attachments, and a death drive, the source of compulsive repetition, hate, aggression and neurotic guilt. In his later works, Freud developed a wide-ranging interpretation and critique of religion and culture.