Erich Neumann
Author: Erich Neumann
Publisher: Princeton University Press (1954)

Evil, no matter by what cultural canon it be judged, is a necessary constituent of individuality as its egoism, its readiness to defend itself or to attack, and lastly, as its capacity to mark itself off from the collective and to maintain its 'otherness' in face of the leveling demands of the community.  The shadow roots the personality in the subsoil of the unconscious, and this shadowy link with the archetype of the antagonist, i.e., the devil, is in the deepest sense part of the creative abyss of every living personality.  That is why in myths the shadow often appears as a twin, for he is not just the 'hostile brother,' but the companion and friend, and it is sometimes difficult to tell whether this twin is the shadow or the self, the deathless 'other.