Symbols and the Interpretation of Dreams by Carl Jung

Our new method treats the dream as a spontaneous product of the psyche about which there is no previous assumption except that it somehow makes sense. This is no more than every science assumes, namely that its object is worthy of investigation. No matter how low one's opinion of the unconscious may be, the unconscious is at least on a level with the louse, which, after all, enjoys the honest interest of the entomologist. As to the alleged boldness of the hypothesis that an unconscious psyche exists, I must emphasize that a more modest formulation could hardly be imagined. It is so simple that it amounts to a tautology: a content of consciousness disappears and cannot be reproduced. The best we can say of it is: the thought (or whatever it was) has become unconscious, or is cut off from consciousness, so that it cannot even be remembered. Or else it may happen that we have an inkling or hunch of something which is about to break into consciousness: "something is in the air," "we smell a rat," and so on. To speak under these conditions of latent or unconscious contents is hardly a daring hypothesis.

When something vanishes from consciousness it does not dissolve into thin air or cease to exist, any more than a car disappearing round a corner becomes non-existent. It is simply out of sight, and, as we may meet the car again, so we may come across a thought again which was previously lost. We find the same thing with sensation, as the following experiment proves. If you produce a continuous note on the edge of audibility, you will observe in listening to it that at regular intervals it is audible and inaudible. These oscillations are due to a periodic increase and decrease of attention. The note never ceases to exist with static intensity. It is merely the decrease of attention that causes its apparent disappearance.