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In what way, however, can a case arise in which the intention to sleep meets
with an interruption? The interruption may proceed from an internal excitation
or from an external stimulus. Let us first consider the more obscure and more
interesting case of interruption from within. Observation shows that dreams are
instigated by residues from the previous day - thought-cathexes which have not
submitted to the general withdrawal of cathexes, but have retained in spite of
it a certain amount of libidinal or other interest. Thus the narcissism of
sleep has from the outset had to admit an exception at this point, and it is here
that the formation of dreams takes its start. In analysis we make the
acquaintance of these ‘day’s residues’ in the shape of latent dream-thoughts; and, both
by reason of their nature and of the whole situation, we must regard them as
preconscious ideas, as belonging to the system Pcs.
We cannot proceed any further in explaining the formation of dreams till we
have overcome certain difficulties. The narcissism of the state of sleep
implies a withdrawal of cathexis from all ideas of objects, from both the unconscious
and the preconscious portions of those ideas. If, then, certain day’s residues
have retained their cathexis, we hesitate to suppose that they have acquired
at night so much energy as to compel notice on the part of consciousness; we
should be more inclined to suppose that the cathexis they have retained is far
weaker than that which they possessed during the day. Here analysis saves us
further speculation, for it shows that these day’s residues must receive a
reinforcement which has its source in unconscious instinctual impulses if they are to
figure as constructors of dreams. This hypothesis presents no immediate
difficulties, for we have every reason to suppose that in sleep the censorship between
the Pcs. and the Ucs. is greatly reduced, so that communication between the two systems is made
easier.