In psychoanalysis, a defence mechanism whereby an emotional conflict associated with an action is dealt with by negating the action or attempting ‘magically’ to cause it not to have occurred by substituting an approximately opposite action. It differs from an ordinary act of making amends for an action that one regrets, inasmuch as the original action itself, and not merely its consequences, are negated. Sigmund Freud (1856–1939) introduced the concept briefly in his famous case study of the ‘Rat Man’ entitled ‘Notes upon a Case of Obsessional Neurosis’ (1909), where he describes compulsive actions ‘in two successive stages, of which the second neutralises the first’ (Standard Edition, X, pp. 155–320, at p. 192). The Rat Man knocked his foot against a stone lying in the road and felt obliged to remove it in case a carriage containing his loved one struck it and caused her to come to grief; but a few minutes later he realized the absurdity of what he had done and felt obliged to put the stone back in its original position in the middle of the road. Freud discussed undoing at greater length in his book Inhibitions, Symptoms and Anxiety (1926), where he gave the clearest definition of it: ‘An action which carries out a certain injunction is immediately succeeded by another action which stops or undoes the first one even if it does not go quite so far as to carry out its opposite’ (Standard Edition, XX, pp. 77–175, at p. 113). Freud's daughter Anna Freud (1895–1982) discussed the phenomenon on page 36 of her book The Ego and the Mechanisms of Defence (1937).