"...Man, as we realize if we reflect for a moment, never perceives nothng fully or comprehends anything completely. He can see, hear, touch and taste; but how far he sees, how well he hears, what his touch tells him, and what he tastes depend upon the number and quality of his senses. These limit his perception of the world around him. By using scientific intruments he can partly compensate for the deficiencies of his senses... But the most elaborate apparatus cannot do more than bring distant or small objects within range of his eyes, or make faint sounds more audible. No matter what instruments he uses, at some point he reaches the edge of certainty beyond which conscious knowledge cannot pass. There are, moreover, unconscious aspects of our percception of reality. The first is the fact that even when our senses react to real phenomena, sights and sounds, they are somehow translated from the realm of reality into that o the mind. Within the mind they become psychic events, hose ultimate nature is unknowable (for the psyche cannot know its own psychical substance). Thus every exxperience contains an indefinite number of unknown factors, not to speak of the fact that every concrete object is always unknown in certain respects, because we cannot know the ultimate nature of matter itself. Then there are certain events of which we have not consciously taken note; they have remained, so to speak, bellow the threshold of conscious knowledge. We can become aware of such happenings only in a moment of intuition or by a process of profound thought that leads to a later realization that they must have happened; and though we may have originally ingnored their emotional and vital importance, it later wells up from the unconscious as a sort of afterthought... Man has developed consciousnes slowly and laboriously, in a process that took untold ages to reach the civilized state (which is arbitrarily dated from the invention of script in about 4000 BC). And this evolution is far from complete, for large areas of the human mind are still shrouded in darkness. What we call the "psyche" is by no means idential with our consciousness and its contents. Whoever denies the existence of the unconscious is in fact assuming that our present knowledge of the psyche is total. And this belief is clearly just as false as the assumption that we know all there is to be known about the natural universe. Our psyche is part of nature, and its enigma is as limitless. Thus we cannot define either the psyche or nature. We can merely state what we believe them to be and describe, as best we can, how they function... We can be possesed and altered by moods, or become unreasonable and unable to recall important facts about ourselves or others. We may think we have ourselves under control; yet a friend can easily tell us things about ourselves of which we have no knowledge. Beyond doubt, even in what we call a high level of civilization, human consciousness has not yet achieved a reasonable degree of continuity. It is still vulnerable and liablle to fragmentation. This capacity to isolate part of one's mind, indeed, is a valuable characteristic. It enables us to concentrate upon one thing at a time, excluding everything else that may claim our attention... A patient, for instance, who is confronted with an intolerable situation may develop a spasm whenever he tries to swallow: He "can't swallow it". Under similar conditions of psychological stress, another patient has an attack of asthma He "can't breathe the atmosphere at home". A third suffers from a peculiar paralysis of the legs He "can't go on anymore". A fourth, who vomits when he eats, "cannot digest" some unpleasant fact. I could cite many examples of this kind, but such physical reactions are only one form in which the problems that trouble us unconsciously may xpress themselves. They more often find expression in our dreams".