No one has more strongly emphasized the essential difference between dream-life and waking life and drawn more far reaching conclusions from this difference than G. Th. Fechner in certain observations contained in his Elemente der Psychophysik (Part II, p. 520). He believes that "neither the simple depression of conscious psychic life under the main threshold," nor the distraction of the attention from the influences of the outer world, suffices to explain the peculiarities of dream-life as compared with waking life. He believes, rather, that the arena of dreams is other than the arena of the waking life of the mind. "If the arena of psychophysical activity were the same during the sleeping and the waking state, the dream, in my opinion, could only be a continuation of the waking ideational life at a lower degree of intensity, so that it would have to partake of the form and material of the latter. But this is by no means the case."

What Fechner really meant by such a transposition of the psychic activity has never been made clear, nor has anybody else, to my knowledge, followed the path which he indicates in this remark. An anatomical interpretation in the sense of physiological localization in the brain, or even a histological stratification of the cerebral cortex, must of course be excluded. The idea might, however, prove ingenious and fruitful if it could refer to a psychical apparatus built up of a number of successive and connected systems.

Other authors have been content to give prominence to this or that palpable psychological peculiarity of the dream-life, and even to take this as a starting-point for more comprehensive attempts at explanation.

It has been justly remarked that one of the chief peculiarities of dream-life makes its appearance even in the state of falling asleep, and may be defined as the sleep-heralding phenomenon. According to Schleiermacher (p. 351), the distinguishing characteristic of the waking state is the fact that its psychic activity occurs in the form of ideas rather than in that of images. But the dream thinks mainly in visual images, and it may be noted that with the approach of sleep the voluntary activities become impeded in proportion as involuntary representations make their appearance, the latter belonging entirely to the category of images. The incapacity for such ideational activities as we feel to be deliberately willed, and the emergence of visual images, which is regularly connected with this distraction- these are two constant characteristics of dreams, and on psychological analysis we are compelled to recognize them as essential characteristics of dream-life. As for the images themselves the hypnogogic hallucinations- we have learned that even in their content they are identical with dream-images. *

* Silberer has shown by excellent examples how in the state of falling asleep even abstract thoughts may be changed into visible plastic images, which, of course, express them. (Jahrbuch, Bleuler-Freud, vol. i, 1900.) I shall return to the discussion of his findings later on.

Dreams, then, think preponderantly, but not exclusively, in visual images. They make use also of auditory images, and, to a lesser extent, of the other sensory impressions. Moreover, in dreams, as in the waking state, many things are simply thought or imagined (probably with the help of remnants of verbal conceptions). Characteristic of dreams, however, are only those elements of their contents which behave like images, that is, which more closely resemble perceptions than mnemonic representations. Without entering upon a discussion of the nature of hallucinations- a discussion familiar to every psychiatrist- we may say, with every well-informed authority, that the dream hallucinates- that is, that it replaces thoughts by hallucinations. In this respect visual and acoustic impressions behave in the same way. It has been observed that the recollection of a succession of notes heard as we are falling asleep becomes transformed, when we have fallen asleep, into a hallucination of the same melody, to give place, each time we wake, to the fainter and qualitatively different representations of the memory, and resuming, each time we doze off again, its hallucinatory character.

The transformation of an idea into a hallucination is not the only departure of the dream from the more or less corresponding waking thought. From these images the dream creates a situation; it represents something as actually present; it dramatizes an idea, as Spitta (p. 145) puts it. But the peculiar character of this aspect of the dream-life is completely intelligible only if we admit that in dreaming we do not as a rule (the exceptions call for special examination) suppose ourselves to be thinking, but actually experiencing; that is, we accept the hallucination in perfectly good faith. The criticism that one has experienced nothing,