In psychoanalysis, the term "libido" is used to describe a mental -- psychic and emotional -- energy associated with instinctual biological drives.
The term "libido" was introduced into psychoanalytic theory by Freud.
Freud often employs metaphors from the science of hydraulics to describe libido.
Freud conceives of the libido as an "economic" concept.
It is said to be quantifiable, plastic and adhesive, and can be attached to or withdrawn from objects thanks to the mechanism of cathexis.
It is an energy which can increase or descrease, and which can be displaced.<ref>Freud, Sigmund. SE XVIII. 1921c. p.90.</ref>
It can be desexualized or used in sublimation.
Freud insisted on the sexual nature of this energy.
Libido is a specifically sexual energy.
Libido is also described by Freud as being active and masculine.
Throughout his work, Freud maintained a dualism in which the libido is opposed to another (non-sexual) form of energy.
Freud made a distinction between the sexual or libidinal drives and the self-preservation of ego drives.
One of the major sources of the disagreement between Freud and Jung is the later's tendency to desexualize the concept of libido and to dissolve it into a more general category of mental energy.
Jung opposed this dualism, positing a single form of life-energy which is neutral in character, and proposed that this energy be denoted by the term "libido."
Lacan uses the term "libido" very sparingly, and tends to discuss sexuality in terms of desire and jouissance.
In general Lacan does not use the term "libido" anywhere near as frequently as Freud, preferring to reconceptualize sexual energy in terms of jouissance.
Lacan rejects Jung's monism and reaffirms Freud's dualism.<ref>Lacan, Jacques. The Seminar. Book I. Freud's Papers on Technique, 1953-54. Trans. John Forrester. New York: Nortion; Cambridge: Cambridge University Press, 1988. p.119-20</ref>
He argues, with Freud, that the libido is exclusively sexual.
Lacan also follows Freud in affirming that the libido is exclusively masculine.<ref>Lacan, Jacques. Écrits: A Selection. Trans. Alan Sheridan. London: Tavistock Publications, 1977. p.291</ref>
In the 1950s Lacan locates the libido in the imaginary order.
"Libido and the ego are on the same side. Narcissism is libidinal."<ref>Lacan, Jacques. The Seminar. Book II. The Ego in Freud's Theory and in the Technique of Psychoanalysis, 1954-55. Trans. Sylvana Tomaselli. New York: Nortion; Cambridge: Cambridge Unviersity Press, 1988. p.326</ref>
From 1964 on, however, there is a shift to articulating the libido more with the real.<ref>Lacan, Jacques. Écrits. Paris: Seuil, 1966. p.848-9</ref>