Principle of least expenditure of innervation

The Principle of least expenditure of innervation is the economy governing the second psychical system: it keeps most excitation quiescent and uses only a limited charge for thought and displacement, preserving the capacity to act upon the external world. In the account of repression, this economy is joined to the unpleasure principle, because thought can take up an unpleasant memory only by inhibiting the discharge that would produce unpleasure.

The Economy of the Second System

The second system must feel its way among memories, emitting and withdrawing charges as it explores possible paths of thought. It needs access to a broad store of memory and firmly established associations, but sending large quantities of energy down particular thought-paths would waste effort in discharges that do not change the world. Its economy therefore consists in keeping the greater part of its energy-charges quiescent and using a smaller portion for displacement.

The contrast is with the first system, whose activity is directed toward freely discharging excitation. The second system inhibits that discharge by emitting its own charges, transforming excitation into a quiescent state and probably raising its level. Once its exploratory thought-activity is complete, it suspends this inhibition, allowing the excitation to be discharged in movement. The economy is thus not the abolition of action: it postpones discharge so that energy can be directed toward effective action rather than dissipated along unproductive paths.

From Wish to Effective Action

The principle belongs to an account of how the psychical apparatus moves from wishing to action. An initial wish may hallucinatorily recharge the memory of a past satisfaction, but hallucination cannot end the need. A second system is required to divert excitation away from perception and toward voluntary movement, which alters the external world and makes an actual perception of the desired object possible.

That practical task requires extensive memory and associations, while also making economy essential. The second system’s exploratory charges must not drain the energy needed for changing external circumstances. In this model, thought is a detour from the memory of satisfaction toward a renewed charge of that memory, sought through motor experience; conserving excitation makes the detour useful rather than merely repetitive.

Unpleasure and Repression

The same inhibition that economizes discharge also explains the avoidance of painful memory. When an external shock produces pain, the primitive apparatus responds with spasmodic movement until it escapes the perception; if the painful perception returns, flight is repeated. A painful memory, when aroused, likewise prompts the primary apparatus to turn away, since overflowing excitation would begin to produce unpleasure. This effortless avoidance supplies the text’s model for psychical repression.

The first system, governed by the unpleasure principle, cannot incorporate anything unpleasant into its train of thought; left to itself, it can only wish. Yet the second system needs access to memories if it is to think. It cannot simply disregard unpleasure, because that principle also regulates its course of excitation. Instead, it must charge a memory in a way that inhibits discharge and prevents unpleasure from developing. Its inhibition need not be complete: the beginnings of unpleasure can still signal what the memory contains and whether it is unsuitable for the thinking-process.

The Principle’s Theoretical Role

The Principle of least expenditure of innervation and the unpleasure principle jointly support the hypothesis that charging by the second system inhibits excitation’s discharge. The second system can take up an idea only when it can inhibit the unpleasure issuing from it; what escapes that inhibition is promptly dropped. Economy is therefore not just a quantitative preference for conserving energy. It helps describe the conditions under which thought can engage material that the primary system would avoid.

This distinction also marks the difference between the primary and secondary processes. The primary process seeks discharge and perceptual identity; the secondary process inhibits that immediate aim and pursues thought-identity instead. The principle helps explain how restrained, exploratory thought can preserve the possibility of later movement while avoiding the useless expenditure of excitation.