the smallest expenditure of innervation.  Let us, however, keep to the fact—­this is the key to the theory of repression—­that the second system is capable of occupying an idea only when it is in position to check the development of pain emanating from it.  Whatever withdraws itself from this inhibition also remains inaccessible for the second system and would soon be abandoned by virtue of the principle of pain.  The inhibition of pain, however, need not be complete; it must be permitted to begin, as it indicates to the second system the nature of the memory and possibly its defective adaptation for the purpose sought by the mind.

The psychic process which is admitted by the first system only I shall now call the primary process; and the one resulting from the inhibition of the second system I shall call the secondary process.  I show by another point for what purpose the second system is obliged to correct the primary process.  The primary process strives for a discharge of the excitement in order to establish a perception identity with the sum of excitement thus gathered; the secondary process has abandoned this intention and undertaken instead the task of bringing about a thought identity.  All thinking is only a circuitous path from the memory of gratification taken as an end-presentation to the identical occupation of the same memory, which is again to be attained on the track of the motor experiences.  The state of thinking must take an interest in the connecting paths between the presentations without allowing itself to be misled by their intensities.  But it is obvious that condensations and intermediate or compromise formations occurring in the presentations impede the attainment of this end-identity; by substituting one idea for the other they deviate from the path which otherwise would have been continued from the original idea.  Such processes are therefore carefully avoided in the secondary thinking.  Nor is it difficult to understand that the principle of pain also impedes the progress of the mental stream in its pursuit of the thought identity, though, indeed, it offers to the mental stream the most important points of departure.  Hence the tendency of the thinking process must be to free itself more and more from exclusive adjustment by the principle of pain, and through the working of the mind to restrict the affective development to that minimum which is necessary as a signal.  This refinement of the activity must have been attained through a recent over-occupation of energy brought about by consciousness.  But we are aware that this refinement is seldom completely successful even in the most normal psychic life and that our thoughts ever remain accessible to falsification through the interference of the principle of pain.