The basic postulate of psychoanalysis, the concept of a dynamic unconscious mind, grew out of Freud's observation that the physical symptoms of hysterical patients tended to disappear after apparently forgotten material was made conscious (see hysteria). He saw the unconscious as an area of great psychic activity, which influenced personality and behavior but operated with material not subject to recall through normal mental processes. Freud postulated that there were a number of defense mechanisms—including repression, reaction-formation, regression, displacement, and rationalization—that protect the conscious mind from those aspects of reality it may find difficult to accept. The major defense mechanism is repression, which induced a "forgetfulness" for harsh realities. Observing the relationship between psychoneurosis and repressed memories, Freud made conscious recognition of these forgotten experiences the foundation of psychoanalytic therapy. Hypnosis was the earliest method used to probe the unconscious, but due to its limited effectiveness, it was soon discarded in favor of free association (see also hypnotism). Dreams, which Freud interpreted as symbolic wish fulfillments, were considered a primary key to the unconscious, and their analysis was an important part of Freudian therapy.
To clarify the operation of the human psyche, Freud and his followers introduced a vast body of psychoanalytic theory. In considering the human personality as a whole, Freud divided it into three functional parts: id, ego, and superego. He saw the id as the deepest level of the unconscious, dominated by the pleasure principle, with its object the immediate gratification of instinctual drives. The superego, originating in the child through an identification with parents, and in response to social pressures, functions as an internal censor to repress the urges of the id. The ego, on the other hand, is seen as a part of the id modified by contact with the external world. It is a mental agent mediating among three contending forces: the outside demands of social pressure or reality, libidinal demands for immediate satisfaction arising from the id, and the moral demands of the superego. Although considered only partly conscious, the ego constitutes the major part of what is commonly referred to as consciousness. Freud asserted that conflicts between these often-opposing components of the human mind are crucial factors in the development of neurosis.
Psychoanalysis focused on early childhood, postulating that many of the conflicts which arise in the human mind develop in the first years of a person's life. Freud demonstrated this in his theory of psychosexuality, in which the libido (sexual energy) of the infant progressively seeks outlet through different body zones (oral, anal, phallic, and genital) during the first five to six years of life.