_Objectivity of Dreams._--In waking life we distinguish ideas or mental images from real objects by the fact that we are able under normal circumstances to dismiss the former at will. In sleep, on the other hand, we have, in the first place, no real objects with which to compare the images, which therefore take on a character of reality comparable to the hallucination of waking life; moreover, powers of visualization and other faculties are enhanced in sleep, so that the strength of dream images considerably exceeds those of the mental images of the ordinary man; changes in powers of attention, volition and memory help to increase the hallucinatory force of the dream. In the second place, the ideas of our dreams are presented in the form of images, which we are unable to dismiss; we therefore mistake them for realities, exactly as the sufferer from delirium tremens in waking life is apt to regard his phantoms as real. _Relations of Dreaming and Sleep._--It has been maintained by Hamilton and others (see below, Modern Views) that dreams invariably accompany sleep, and that we always find ourselves dreaming when we are awakened. But even if it were true that dreams were invariably experienced at the moment of waking, this would not by any means establish the invariable concomitance of dreams and sleep of all sorts; at most it would show that imperfect sleep is a condition of dreaming; in the same way, dreams before wakening, known to have taken place either from the recollection of the dreamer or from the observation of another person, may clearly be due to imperfect wakening, followed by a deepening of sleep. It is, however, by no means true that awakening from sleep is invariably accompanied by a dream; in considering the question it must be recollected that it is complicated by the common experience of very rapid forgetfulness of even a vivid and complicated dream, only the fact of having dreamt remaining in the memory; it is clear that amnesia may go so far that even the fact of dreaming may be forgotten. On the whole, however, there appear to be no good grounds for the assertion that we always dream when we are asleep. On the other hand, there is no proof that partial awakening is a necessary condition of dreaming.