In psychoanalysis, the mixing of Eros and Thanatos so that they operate jointly, in contrast to the defusion of instincts in which they operate independently, each pursuing its own instinctual aim. In a key passage on this phenomenon, Sigmund Freud (1856–1939) wrote in his book New Introductory Lectures on Psycho-Analysis (1933, Standard Edition, XXII, pp. 5–182): ‘In sadism and masochism we have before us two excellent examples of a mixture of two classes of instinct, of Eros and aggressiveness; and we proceed to the hypothesis that this relation is a model of one—the very instinctual impulse that we can examine consists of similar fusions or alloys of the two classes of instinct. These fusions, of course, would be in the most varied ratios’ (pp. 104–5).