Kant observed that the madman is a dreamer awake, and more recently Wundt has remarked that, when asleep, we "can experience nearly all the phenomena which meet us in lunatic asylums." The grotesqueness of the combinations, the lack of all judgment as to consistency, fitness, and probability, are common characteristics of the short night-dream of the healthy and the long day-dream of the insane.[100] But one great difference marks off the two domains.

When dreaming, we are still sane, and shall soon prove our sanity.

After all, the dream of the sleeper is corrected, if not so rapidly as the illusion of the healthy waker.

As soon as the familiar stimuli of light and sound set the peripheral sense-organs in activity, and call back the nervous system to its complete round of healthy action, the illusion disappears, and we smile at our alarms and agonies, saying, "Behold, it was a dream!" On the practical side, the illusions and hallucinations of sleep must be regarded as comparatively harmless.

The sleeper, in healthy conditions of sleep, ceases to be an agent, and the illusions which enthral his brain have no evil practical consequences.