A defense mechanism is a psychological mechanism that functions as a form of self-protection in which an undesirable emotion or impulse is avoided or controlled. Sigmund Freud (1856-1939) introduced this idea into psychoanalysis in his article The Infantile Genital Organization (1923).

The concept of defense mechanisms has not lacked criticism but is still important in psychological understanding. Although protective of the self, a defense mechanism can become pathological if used excessively.

Several defense mechanisms have been described:

Denial – This is a refusal of acknowledgment through the failure to consciously acknowledge thoughts, desires, feelings, or aspects of reality that are too painful or unacceptable. An example is an individual with a terminal illness who refuses to acknowledge the imminence of death. 

Displacement – This is the redirection of powerful negative or positive emotions directed toward another object or person.

Externalization – The unconscious attribution of inner impulses to the external world. For example, a child converts his unconscious impulses of anger or aggression into a fear of monsters in the dark. A common form of externalization is projection.

Identification with the aggressor – Articulated by Sigmund Freud’s daughter Anna Freud (1895-1982) in The Ego and the Mechanisms of Defence (1950). It describes a person who when facing an external threat, such as disapproval or criticism from an authority figure, identifies with the source of the threat. The person appropriates the aggression or adopts attributes of the threatening figure.

Introjection – This term was introduced by Hungarian psychoanalyst Sandor Ferenczi (1873-1933) in Introjection and Transference (1916), where he contrasts it with projection. It is instinctual energy that is turned inward such as, for example, when a depressed person turns aggression back on himself. 

Projection – The attribution of one’s intolerable feelings, impulses, or thoughts to other people. Sigmund Freud studied this in connection to paranoia, although he never completed his analysis of it in full.

Rationalization – First used by Ernest Jones (1879-1958) in the Journal of Abnormal Psychology, rationalization is a contrived false but reassuring or self-serving explanation to explain behavior that arises from a repressed wish. It works on the unconscious level to help protect the mind from feelings of anxiety, such as when one convinces herself that a particular situation is “really not that bad”.

Reaction formation – When a feeling or idea is felt to be especially threatening, the person deals with it by enthusiastically embracing its opposite. For example, a man who is threatened by his homosexual feelings might engage in aggressive heterosexual behavior, or when a shy person behaves in an exhibitionist manner.

Regression – Sigmund Freud introduced this mechanism in The Interpretation of Dreams (1899). It describes a person who reverts to a form of behavior or thinking characteristic of an earlier stage of development to avoid or reduce anxiety, such as when an adult experiencing stress resorts to behaving in a childlike manner.

Repression – Described in Sigmund Freud’s article Repression (1915), this is when unacceptable thoughts, feelings, or wishes are banished from consciousness or, in Freud’s words, “turning something away, and keeping it at a distance, from the conscious”.

Sublimation – When an unconscious or repressed drive is denied gratification leading to the diversion of the drive into a more acceptable form of expression. For example, aggression is diverted into playing or watching violent sports. In Civilization and its Discontents, Sigmund Freud attributed the highest expressions of civilization to the sublimation of the sexual drive.

Suppression – In The Interpretation of Dreams, suppression is described as the elimination or banishing of feelings, wishes, or memories from a person’s consciousness. It differs from repression because the eliminated material is stored in the preconscious rather than the unconscious.