Interpretation means finding a hidden meaning. There can be no question of interpretation in such an estimation of the dream process. Look up the description of the dream in Wundt, Jodl and other newer philosophers. You will find an enumeration of the deviations of dream life from waking thought, in a sense disparaging to the dream. The description points out the disintegration of association, the suspension of the critical faculty, the elimination of all knowledge, and other signs of diminished activity. The only valuable contribution to the knowledge of the dream which we owe to exact science pertains to the influence of bodily stimuli, operative during sleep, on the content of the dream. There are two thick volumes of experimental researches on dreams by the recently deceased Norwegian author, J. Mourly Vold, (translated into German in 1910 and 1912), which deal almost solely with the consequences of changes in the position of the limbs. They are recommended as the prototype of exact dream research. Now can you imagine what exact science would say if it discovered that we wish to attempt to find the meaning of dreams? It may be it has already said it, but we will not allow ourselves to be frightened off. If errors can have a meaning, the dream can, too, and errors in many cases have a meaning which has escaped exact science. Let us confess to sharing the prejudice of the ancients and the common people, and let us follow in the footsteps of the ancient dream interpreters. First of all, we must orient ourselves in our task, and take a bird's eye view of our field. What is a dream? It is difficult to say in one sentence. But we do not want to attempt any definition where a reference to the material with which everyone is familiar suffices. Yet we ought to select the essential element of the dream. How can that be found? There are such monstrous differences within the boundary which encloses our province, differences in every direction. The essential thing will very probably be that which we can show to be common to all dreams. Well, the first thing which is common to all dreams is that we are asleep during their occurrence. The dream is apparently the psychic life during sleep, which has certain resemblances to that of the waking condition, and on the other hand is distinguished from it by important differences. That was noted even in Aristotle's definition. Perhaps there are other connections obtaining between the dream and sleep. One can be awakened by a dream, one frequently has a dream when he wakes spontaneously or is forcibly awakened from sleep. The dream then seems to be an intermediate condition between sleeping and waking. Thus we are referred to the problem of sleep. What, then, is sleep?