In psychoanalysis, any of the basic elements of the sexual instinct as defined by its instinctual source (oral, anal, and so on) and to a lesser extent by its instinctual aim and instinctual object. Sigmund Freud (1856–1939) introduced the concept in 1905 in his book Three Essays on the Theory of Sexuality (Standard Edition, VII, pp. 130–243). In one of his encyclopedia articles published in 1923, he explained: ‘The sexual instinct, the dynamic manifestation of which in mental life we shall call “libido”, is made up of component instincts into which it may once more break up and which are only gradually united into well-defined organizations. … The first (pregenital) stage of organization to be discerned is the oral one’ (Standard Edition, XVIII, pp. 235–59, at p. 244). Also called an instinctual component, a partial instinct, or a part instinct.