That a dream fades away in the morning is proverbial. It is, indeed, possible to recall it. For we know the dream, of course, only by recalling it after waking; but we very often believe that we remember it incompletely, that during the night there was more of it than we remember. We may observe how the memory of a dream which in the morning was still vivid fades in the course of the day, leaving only a few trifling remnants. We are often aware that we have been dreaming, but we do not know of what we have dreamed; and we are so well used to this fact- that the dream is liable to be forgotten- that we do not reject as absurd the possibility that we may have been dreaming even when, in the morning, we know nothing either of the content of the dream or of the fact that we have dreamed. On the other hand, it often happens that dreams manifest an extraordinary power of maintaining themselves in the memory. I can remember a dream of my own which has lost nothing of its freshness in my memory. All this is very remarkable, and for the present incomprehensible...