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The processes of the system Ucs. are timeless; i.e. they are not ordered temporally, are not altered by the passage of
time; they have no reference to time at all. Reference to time is bound up, once
again, with the work of the system Cs.
The Ucs. processes pay just as little regard to reality. They are subject to the pleasure principle; their fate depends only on how
strong they are and on whether they fulfil the demands of the
pleasure-unpleasure regulation.
To sum up: exemption from mutual contradiction, primary process (mobility of cathexes), timelessness, and replacement of external by psychical reality - these are the characteristics which we may expect to find in processes
belonging to the system Ucs.¹
Unconscious processes only become cognizable by us under the conditions of
dreaming and of neurosis - that is to say, when processes of the higher, Pcs., system are set back to an earlier stage by being lowered (by regression). In
themselves they cannot be cognized, indeed are even incapable of carrying on
their existence; for the system Ucs. is at a very early moment overlaid by the Pcs. which has taken over access to consciousness and to motility. Discharge from
the system Ucs. passes into somatic innervation that leads to development of affect; but even
this path of discharge is, as we have seen, contested by the Pcs. By itself, the system Ucs. would not in normal conditions be able to bring about any expedient muscular
acts, with the exception of those already organized as reflexes.
¹ We are reserving for a different context the mention of another notable
privilege of the Ucs.