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. 2. Theories which, on the contrary, assume for the dream a diminution for the psychic activity, a loosening of the connections, and an impoverishment in available material. In accordance with these theories, one must assume for sleep a psychological character entirely different from the one given by Delbœuf. Sleep extends far beyond the mind—it does not consist merely in a shutting off of the mind from the outer world; on the contrary, it penetrates into its mechanism, causing it at times to become useless. If I may draw a comparison from psychiatrical material, I may say that the first theories construct the dream like a paranoia, while the second make it after the model of a dementia or an amentia. The theory that only a fragment of the psychic activity paralysed by sleep comes to expression is by far the favourite among the medical writers and in the scientific world. As far as one may presuppose a more general interest in dream interpretation, it may well be designated as the ruling theory of the dream. It is to be emphasized with what facility this particular theory escapes the worst rock threatening every dream interpretation, that is to say, being shipwrecked upon one of the contrasts embodied in the dream. As this theory considers the dream the result of a partial waking (or as Herbart’s _Psychology_ of the dream says, “a gradual, partial, and at the same time very anomalous waking”), it succeeds in covering the entire series of inferior activities in the dream which reveal themselves in its absurdities, up to the full concentration of mental activity, by following a series of states which become more and more awake until they reach full awakening. One who finds the psychological mode of expression indispensable, or who thinks more scientifically, will find this theory of the dream expressed in the discussion of Binz[4] (p. 43):—