psychical appearance of probability; the
child is without the capacity which it will acquire later to distinguish
hallucinations or phantasies from reality.

The adult has learnt this differentiation; he has also learnt the
futility of desire, and by continuous practice manages to postpone his
aspirations, until they can be granted in some roundabout method by a
change in the external world. For this reason it is rare for him to have
his wishes realized during sleep in the short psychical way. It is even
possible that this never happens, and that everything which appears to
us like a child's dream demands a much more elaborate explanation. Thus
it is that for adults--for every sane person without exception--a
differentiation of the psychical matter has been fashioned which the
child knew not. A psychical procedure has been reached which, informed
by the experience of life, exercises with jealous power a dominating and
restraining influence upon psychical emotions; by its relation to
consciousness, and by its spontaneous mobility, it is endowed with the
greatest means of psychical power. A portion of the infantile emotions
has been withheld from this procedure as useless to life, and all the
thoughts which flow from these are found in the state of repression.

Whilst the procedure in which we recognize our normal ego reposes upon
the desire for sleep, it appears compelled by the psycho-physiological
conditions of sleep to abandon some of the energy with which it was wont
during the day to keep down what was repressed. This neglect is really
harmless; however much the emotions of the child's spirit may be
stirred, they find the approach to consciousness rendered difficult, and
that to movement blocked in consequence of the state of sleep. The
danger of their disturbing sleep must, however, be avoided. Moreover, we
must admit that even in deep sleep some amount of free attention is
exerted as a protection against sense-stimuli which might, perchance,
make an awakening seem wiser than the continuance of sleep. Otherwise we
could not explain the fact of our being always awakened by stimuli of
certain quality. As the old physiologist Burdach pointed out, the mother
is awakened by the whimpering of her child, the miller by the cessation
of his mill, most people by gently calling out their names. This
attention, thus on the alert, makes use of the internal stimuli arising
from repressed desires, and fuses them into the dream,