I'm going to follow Campbell's outline of Jung's theory as he lays it out in "Psyche and Symbol," the first lecture in the series, Mythos 1: the Shaping of Our Mythic Tradition. The third of the Archetypes that Campbell discusses (and one of my favorites) is the Shadow.
Here's what Campbell has to say:
Near the bottom of the circle is the “shadow,” as Jung calls it, which we have depicted as a series of separate strokes. The shadow is like the blind spot for the ego: that part of the self about which ego is completely unconscious.
Jung's first interest in Freud was in Freud's theory of the mechanism of repression. What is it in the psyche, Freud asked, that puts certain experiences so out of sight that consciousness is completely unaware of them? Jung's shadow corresponds almost precisely to the Freudian unconscious, which is constituted of shocks that have been experienced and then repressed by the infant and the growing child. The shocks that upset and transform the life experience of one person are never precisely the same as those that have affected another, so these experiences set up an individual’s posture, his structuring attitude toward life
Yet the shadow, this system of individual shocks, and the self, which is a function of basic human biology, both exist in the unconscious realm as far as ego knowledge is concerned. So there must be, Jung argued, two orders to the unconscious: the realm common to all, which he called the “collective” unconscious, and that which he termed the “personal” unconscious, the realm unique to each individual. It is out of these centers that dreams emerge.
Most dreams, of course, are personally oriented: they come from the personal unconscious and are related to experiences quite peculiar to the individual. The order of symbols in these dreams can be interpreted by personal associations—the free-association technique that Freud used. Yet there will be other images in dreams at certain critical moments in life that cannot be interpreted through personal associations, for they are strictly mythological in character. Mythological imagery evolves from the collective unconscious. Jung calls dreams arising from the personal unconscious “little” dreams; the others, he calls “big” dreams. Big dreams often occur in Technicolor.
Joseph Campbell Foundation
publications at jcf dot org
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