Personality refers to unique patterns of thinking, feeling and behaving. There are several perspectives on personality including psychoanalytic, humanistic, social cognitive and trait theories. The psychoanalytic perspective emphasizes unconscious motivations and was developed by Sigmund Freud who described the id, ego and superego. Defense mechanisms and psychosexual stages are also part of psychoanalytic theory. Personality is assessed using both projective tests and self-report inventories which each have strengths and weaknesses.