The concepts of fusion and defusion essentially apply to the life and death instincts, which are initially closely united but later become partially differentiated, under the influence of various psychic movements. Some portion of these instincts remains fused together in the self, in the form of erotogenic masochism (Laplanche and Pontalis, 1967, pp. 244-245).
The elaboration of the second theory of the instincts in "Beyond the Pleasure Principle" (1920g) led Sigmund Freud to postulate the existence of two types of instincts: the life instinct, which forms ever-larger units, and the death instinct, which disintegrates these units. Fusion of the life and death instincts is primal. Outward projection of the death instinct, when it is redirected inward toward the self, constitutes secondary masochism, Freud asserted in "The Economic Problem of Masochism" (1924c). But, according to Freud, a psychic movement that inhibits libidinal satisfaction, such as the movement that is the basis for the existence of the superego or the process of sublimation, by its very nature brings about a defusion of the instincts and thus unleashes destructiveness. This is what endows the Superego with a brutal and cruel aspect, Freud explained in "The Ego and the Id" (1923b).
Benno Rosenberg, in his thorough study of the consequences of this theory of fusion of the instincts, postulated the existence of a form of "life-saving masochism," so named because it restrains primal destructiveness in its structures. Nevertheless, there is a remaining ambiguity: When Jean Laplanche in The Language of Psychoanalysis (1967, trans. 1974) deemed the term union preferable to fusion, he introduced the concept of binding (Wilfred R. Bion), which has generally supplanted the concept of fusion in the current psychoanalytic literature. However, the concept of binding/unbinding applies to that which interrelates or separates the ego and the object, and no longer applies to the two types of instincts.
It has come to the point where the term fusion is often used instead of binding ; there is thus a confusion between that which pertains to the integration of opposite qualities, with all the mental work that entails, and what was originally conceived as a primal attribute of the psyche. This confusion particularly affects the concept of ambivalence, which is the maintaining of two distinct qualities that exist in conjunction but not in a state of fusion.
See also: Activity/passivity; Binding/unbinding of the instincts; Death instinct (Thanatos); Economic point of view; Eros; Free energy/bound energy; Ego and the Id, The ; Life instinct (Eros); Love-Hate-Knowledge (L/H/K links); Sexuality.
Freud, Sigmund. (1920). Beyond the pleasure principle. SE, 18, 7-64.
——. (1923). The ego and the id. SE, 19, 12-66.
——. (1924). The economic problem of masochism. SE, 19, 159-70.
Laplanche, Jean, and Pontalis, Jean-Bertrand. (1974). The language of psycho-analysis. (Donald Nicholson-Smith, Trans.). New York: Norton.
Rosenberg, Benno. (1991). Masochisme mortifère et masochisme gardien de la vie. (pp. 30-54). Paris: Presses Universitaires de France.