We have so far discussed the dream-wish, we have traced it to the sphere of the Unc., and analyzed its relations to the day remnants, which in turn may be either wishes, psychic emotions of any other kind, or simply recent impressions.  We have thus made room for any claims that may be made for the importance of conscious thought activity in dream formations in all its variations.  Relying upon our thought series, it would not be at all impossible for us to explain even those extreme cases in which the dream as a continuer of the day work brings to a happy conclusion and unsolved problem possess an example, the analysis of which might reveal the infantile or repressed wish source furnishing such alliance and successful strengthening of the efforts of the foreconscious activity.  But we have not come one step nearer a solution of the riddle:  Why can the unconscious furnish the motive power for the wish-fulfillment only during sleep?  The answer to this question must throw light on the psychic nature of wishes; and it will be given with the aid of the diagram of the psychic apparatus.

We do not doubt that even this apparatus attained its present perfection through a long course of development.  Let us attempt to restore it as it existed in an early phase of its activity.  From assumptions, to be confirmed elsewhere, we know that at first the apparatus strove to keep as free from excitement as possible, and in its first formation, therefore, the scheme took the form of a reflex apparatus, which enabled it promptly to discharge through the motor tracts any sensible stimulus reaching it from without.  But this simple function was disturbed by the wants of life, which likewise furnish the impulse for the further development of the apparatus.  The wants of life first manifested themselves to it in the form of the great physical needs.  The excitement aroused by the inner want seeks an outlet in motility, which may be designated as “inner changes” or as an “expression of the emotions.”  The hungry child cries or fidgets helplessly, but its situation remains unchanged; for the excitation proceeding from an inner want requires, not a momentary outbreak, but a force working continuously.  A change can occur only if in some way a feeling of gratification is experienced—­which in the case of the child must be through outside help—­in order to remove the inner excitement.  An essential constituent of this experience is the appearance of a certain perception (of food in our example), the memory picture of which thereafter remains associated with the memory trace of the excitation of want.