The term "defense" refers to all the techniques deployed by the ego in conflicts that have the potential to lead to neurosis. In the sense in which Freud first used the term, defenses are unconscious because they stem from a conflict between the drive and the ego or between a perception or representation (memory, fantasy, etc.) and moral imperatives. The function of the defenses is thus to support and maintain a state of psychic stability by avoiding anxiety and unpleasure. The concept of defense was broadened somewhat when Freud attributed an important role to the reality principle and to the superego. Melanie Klein then formed the more radical view that the defenses exist within an archaic ego.

In his letter to Wilhelm Fliess dated May 21, 1894, and concerning his interpretation of the neuroses, Freud introduced the concept of defense in connection with the notion of psychic conflict: "What is warded off is always sexuality"...