in classical psychoanalytic theory, mental structures and mechanisms. Sigmund Freud initially (1900) divided these into unconscious, preconscious, and conscious areas or systems and later (1923) into the id, ego, and superego: The id is described as unconscious, and the ego and superego as partly conscious, partly preconscious, and partly unconscious. Also called mental apparatus. See also structural model; topographic model.