which at the same time determines the relation of the dream to a more comprehensive sphere of manifestations, may be called a theory of dreams. Individual theories of the dream will be distinguished from one another through the fact that they raise to prominence this or that characteristic of the dream, and connect explanations and relations with it. It will not be absolutely necessary to derive from the theory a function, i.e. a use or any such activity of the dream, but our expectation, which is usually adjusted to teleology, will nevertheless welcome those theories which promise an understanding of the function of the dream.
We have already become acquainted with many conceptions of the dream which, more or less, merit the name of dream theories in this sense. The belief of the ancients that the dream was sent by the gods in order to guide the actions of man was a complete theory of the dream giving information concerning everything in the dream worth knowing. Since the dream has become an object of biological investigation we have a greater number of theories, of which, however, some are very incomplete.
If we waive completeness, we may attempt the following loose grouping of dream theories based on their fundamental conception of the degree and mode of the psychic activity in the dream:—
1. Theories, like those of Delbœuf,16 which allow the full psychic activity of the waking state to continue into the dream. Here the mind does not sleep; its apparatus remains intact, and, being placed under the conditions different from the waking state, it must in normal activity furnish results different from those of the waking state. In these theories it is a question whether they are in position to derive the distinctions between dreaming and waking thought altogether from the determinations of the sleeping state. They moreover lack a possible access to a function of the dream; one cannot understand why one dreams, why the complicated mechanism of the psychic apparatus continues to play even when it is placed under conditions for which it is not apparently adapted. There remain only two expedient reactions—to sleep dreamlessly or to awake when approached by disturbing stimuli—instead of the third, that of dreaming.
