IV. Psychic Exciting Sources.—In treating the relations of the dream to the waking life and the origin of the dream material, we learned that the earliest as well as the latest investigators agreed that men dream of what they are doing in the day-time, and of what they are interested in during the waking state. This interest continuing from waking life into sleep, besides being a psychic tie joining the dream to life, also furnishes us a dream source not to be under-estimated, which, taken with those stimuli which become interesting and active during sleep, suffices to explain the origin of all dream pictures. But we have also heard the opposite of the above assertion, viz. that the dream takes the sleeper away from the interests of the day, and that in most cases we do not dream of things that have occupied our attention during the day until after they have lost for the waking life the stimulus of actuality. Hence in the analysis of the dream life we are reminded at every step that it is inadmissible to frame general rules without making provision for qualifications expressed by such terms as "frequently," "as a rule," "in most cases," and without preparing for the validity of the exceptions.
If the conscious interest, together with the inner and outer sleep stimuli, sufficed to cover the etiology of the dreams, we ought to be in a position to give a satisfactory account of the origin of all the elements of a dream; the riddle of the dream sources would thus be solved, leaving only the task of separating the part played by the psychic and the somatic dream stimuli in individual dreams. But as a matter of fact no such complete solution of a dream has ever been accomplished in any case, and, what is more, every one attempting such solution has found that in most cases there have remained a great many components of the dream, the source of which he was unable to explain. The daily interest as a psychic source of dreams is evidently not far-reaching enough to justify the confident assertions to the effect that we all continue our waking affairs in the dream.Other psychic sources of dreams are unknown. Hence, with the exception perhaps of the explanation of dreams given by Scherner,58 which will be referred to later, all explanations found in the literature show a large gap when we come to the derivation of the material for the presentation pictures, which