the fourth, undifferentiated, “inferior” function is undomesticated, unadapted, uncontrolled, and primitive. Because of its contamination with the collective unconscious, it possesses archaic and mystical qualities
This passage directly identifies the fourth function as the psychologically primitive, unconscious-contaminated complement to three differentiated functions, grounding the Jungian typological schema in the Platonic axiom of Maria Prophetissa.
, The Psyche in Antiquity, Book One: Early Greek Philosophy From Thales to Plotinus, 1999thesis