The Collective Unconscious
Jung's most contested proposition: a stratum of the psyche older than biography, organized not by personal experience but by inherited form.
Freud's unconscious was personal — a basement of forgotten, repressed, or socially unacceptable material drawn from the individual's own life. Jung accepted this layer and then argued there was another beneath it, common to the species.
The evidence he marshalled was comparative. Patients with no exposure to a given mythology produced its motifs in dreams. Schizophrenic delusions reproduced cosmologies the patient could not have read. The same handful of figures — the wise old man, the great mother, the child, the trickster, the shadow — appeared in cultures separated by oceans and centuries.
The collective unconscious is not a library of inherited memories. It is a set of inherited structures of possibility — what Jung called archetypes — that organize experience the way grammar organizes language. The contents that fill those structures are local; the structures themselves are not.
This is the proposition that makes Jungian work strange to a strictly empirical psychology and indispensable to anyone who takes seriously the recurrence of pattern across human experience.