Instinct, for both psychology and ethology is a preformed behavioral patternoften manifesting itself immediately from birth. Its arrangement is determined hereditarily and is repeated according to modalities relatively adapted to a certain kind of object. (from Laplanche, Life and Death in Psychoanalysis) Instinctive behaviour contributes to the survival of species and is evolved like morphological structure. (Bowlby) Charles Darwin outlined the modern theory of instinct in The Origin of Species.

For Descartes, instinct was "a Kind of Inspiration to Brutes, mixing itself with, and helping out, that Part of their Faculties which corresponds to Reason in us, and which is extremely imperfect in them." Erasmus Darwin irritably observed that instinct had "been explained to be a divine something, a kind of inspiration; whilst the poor animal, that possesses it, had been thought little better than a machine!" When coupled with a behavioristic approach, the concept of instinct serves to deny animals any possible consciousness, making the most elaborate behavior one thier part only a machine-like expression of a genetic program. In Animal Minds, Donald R. Griffin ridicules the inhibitions that keep behaviorist scientists from even considering animal consciousness. He describes situations where animals adapt and learn, where they use tools or communicate, and claims that it is far simpler to explain these behaviors through cognitive concepts such as learning, remembering, problem solving, rule and concept formation, perception and recognition, than it is to describe them all as genetically pre-programmed and inflexible behaviors. In the words of Kety (1960,1862) "Nature is an elusive quarry, and it is foolhardy to pursue her with one eye closed and one foot hobbled." (Animal Minds, p.23) For Griffin the accusations of anthropocentrism that are used to deny the possibility of animal consciousness are only expressions of the prejudiced assumption that consciousness is only a human trait. 

Is there a difference between animal instincts and human instincts? Most writers dealing with instinct in humans use the concept to tie human behaviour into an evolutionary framework. At the same time, the apparent variability of human behaviour, even when instinctually driven, requires a more flexible or elaborate theory of instinct. 

The standard concept of instinct, even when it leads to complex behaviour such as nest building, implies predictable sequences of stereotypical responses to precise "releasing stimuli." -- N. Tinbergen, A Study of Instinct, Oxford U. Press, 1969 -- ref. in Ronald de Sousa, The Rationality of Emotion, p. 84. This is the form of instinct that causes a hare to run in a zig-zag pattern, even in front of a car which could avoid it much more easily if it ran in a straight line. ( But how could the hare ever know that the car was controlled by a driver who preferred to avoid it rather than run it down? ) Ronald De Sousa describes human instincts as motivational. They do not determine fixed patterns of behavior, but can produce quite different patterns of goal-oriented behavior in different circumstances. They also involve motivation and emotion. Nonetheless, human instincts must be preprogrammed wants that are the result of evolution. "Rembering the primacy of individual variation over types in modern evolutionary theory, we should not infer that natural instincts, wants, or emotions will be universal ones. Instead, we should assume that we might make sense of the notion of individual natures. " (De Sousa, p. 105)

Sigmund Freud developed his theories of instinct in Three Essays on the Theory of Sexuality (1905), in "Instincts and their Vicissitudes" (1915), and later elaborated a different and more general concept in Beyond the Pleasure Principle. (1920)For Freud, the instinct concept is a borderline concept, on the border between the somatic and the psychic realms. He wavered between characterizing instinct as an organic stimulus -- a "need" affecting the psychic apparatus -- and as a psychic representative of such an organic need-stimulus. This ambiguity lead Freud to wonder, for example, whether it was possible to have instinctual memories. Here the conceptual identification between the instinctive and the unconscious is manifest. 

Freud's term for instinct, Trieb, (from treiben, "to push") is more accurately translated as "instinctual drive," and its translation as "instinct" in the Standard Edition of Freud's work has been a source of criticism and confusion. 

Jean Pontalis points out that Freud uses two distinct words, Instinkt and Trieb, and although their usage overlaps, there remain slight differences of meaning. For Pontalis, the drive is derived from the instinct. He stresses the importance of "propping" -- a translation of Freud's references to anlenhung, usually translated into English as "anaclitic." (fr. étayage)-- as the relation of the drive to nonsexual, vital functions, upon what Freud calls "a bodily function essential to life." If these functions are oriented by instinct, then the drives prop themselves on the instincts. The archetypal model for this relation is orality, which is a sexual process that begins to appear in relation to breast feeding. Thus the instinct is the source of a process that mimics, displaces, and denatures it: the drive. (Laplanche, p.22) (cf desire as a "cartography of the body.)For Jean Pontalis, "It is sexuality which represents the model of every drive and probably consitutes the only drive in the strict sense of the term." (Life and Death in Psychoanalysis, p.8) 

In "Instincts and their Vicissitudes," Freud states that "The aim of an instinct is in every instance satisfaction (Befriedigung ), which can only be obtained by removing the state of stimulation at the source of the instinct." Thus climactic phenomena become the prototype of satisfaction through the discharge of tension (Abfuhr ). This is known as the Nirvana (or constancy) principle, whose satisfaction is the state of rest. Freud goes on to describe how, while the final aim (Endziel ) of an instinct remains unchangable, intermediate aims may arise, which he defines as aim-inhibited instincts. Freud related the growth of civilization to the suppression of the instincts, In Totem and Taboo, "Civilized" Sexual Ethics, and most famously, in Civilization and its Discontents.

For Freud, sublimation was the utilization and transformation of instinctual goals for intellectual and professional achievement. Unlike repression, which runs counter to instinct, sublimation utilizes the instinctual forces by channeling or modeling them. Leonardo da Vinci was the classic case of sublimation, which did not involve repression, even as it left Leonardo without much overt sexual drive. (Freud sees Leonardo's turn to scientific activities as part of a neurotic repression, however. What had started as study in service of his art (eg. anatomy) came to inhibit it.)Later, in 1920, Freud formulated the theory of dual instinctual drives: Eros and Thanatos. (respectively libido-aggression and erotic-destructive)

(Georges Bataille developed the overlap between love and death in Eroticism

The "economic," or discharge, model of instinctual satisfaction required revision to conform to this new conception of the dual instincts: the satisfaction of the life instinct could hardly consist in the elimination of tension, which would at that point be identified with the death instinct. It required qualitative as well as quantitative characteristics. In "The Economic Problem of Masochism" (1924) Freud acknowledged that there must be pleasurable tensions and unpleasurable relaxations of tensions as well. The introduction of the life instinct (which encompassed different conceptions of pleasure and of the pleasure principle) was a true and unsettling innovation in psychoanalytic theory -- an innovation that Freud could no longer circumvent but with which he felt much less at home than he did with the death instinct. (Loewald. p. 30) 

Didier Anzieu describes Freud's own sublimation as reflexive rather than expressive -- as a knowledge of the workings of instinct, which provided only a partial and insufficient discharge of instinctual energies. According to Hans Loewald, in the scientific work of psychoanalysis, sublimation turns around on itself, and as it were against itself --to unmask itself. Loewald emphasizes the symbolic linkages which still obtain between instinctual and deinstinctualized elements. He describes sublimations as progressive differentiations that culminate in new synthetic organizations in which oneness stays alive as connection. see p lay Do humans have a "lang uage instinct?"