Principle of (Neuronal) Inertia

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The principle of inertia is a principle of the functioning of the nervous system in which the ' neurones tend to divest themselves completely of the quantities of energy that they receive. Freud presented it at the beginning of the Project for a Scientific Psychology (1950c [1895]).

The ' neurones receive external excitations, since they belong to consciousness. These neurones are described as "permeable" because their "contact barriers" (what we today would call synapses) permit quantities of energy to pass toward the?, or perceptual, neurones. In the Project, Freud takes the general law of motion from physics as his basis, but then focuses on an active tendency of the system, which would oppose the principle of constancy; in effect, he creates a psychophysical fantasy in which it is the working of the system itselfand not the conservation of energythat is the final goal. The Freudian model here is the reflex arc and, in particular, the "inclination to a flight from pain" caused by an exterior source.

Freud uses the notion of inertia in an ambiguous manner. In the physical sense, it is a property of what he calls "quantity," which, transformed into "quality," is retained by the memory belonging to the w system. The word Tragheit itself adds an unexpected element: in German it means both "inertia" and "laziness." While it may be difficult to think of such an active principle as idle, Freud nonetheless used this ambiguity here to indicate the system's fundamental tendency to retreat from life's burdens. Elsewhere in his work Freud did use Tragheit to mean "laziness," speaking of "mental laziness," "intestinal laziness," "dreams of laziness," and so on. Later, influenced by Jung's term "viscosity of the libido," Freud used the word to mean "inertia," particularly as a synonym for "fixation."

While the "principle of inertia" does not appear again in Freud's work after the Project, he does maintain a permanent equivocation between the different levels "constant," "low," and "zero" (1920g; Laplanche, 1970/1976).

Although it may represent a metaphor for free circulation in the unconscious, the principle of inertia can be considered as an eventual source of errors. Beyond its theoretical heir, the nirvana principle/death drive, it cannot account with any specificity for the encounter on the level of libido between adult and child. On the other hand, the principle of neuronal inertia does offer a certain resemblance to the free circulation of thing-representations that characterizes the unconscious, and it might well describe the results of trauma.

Bertrand Vichyn

See also: Discharge; Facilitation; Primary object; Principle of constancy; Principle of mental functioning; "Project for a Scientific Psychology, A"; Psi (Ψ) system; Word-presentation.


Freud, Sigmund. (1920g). Beyond the pleasure principle. SE, 18: 1-64.

. (1950c [1895]). Project for a scientific psychology. SE, 1: 281-387.

Laplanche, Jean. (1976). Life and death in psychoanalysis (Jeffrey Mehlman, Trans.). Baltimore: Johns Hopkins University Press. (Original work published 1970)

Laplanche, Jean, and Pontalis, Jean-Bertrand. (1974). The language of psycho-analysis (Donald Nicholson-Smith, Trans.). New York: W. W. Norton. (Original work published 1967)

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Principle of (Neuronal) Inertia

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Principle of (Neuronal) Inertia