Carl Jung developed the concepts of the personal unconscious, collective unconscious, and archetypes. The psyche consists of the ego, personal unconscious, and collective unconscious. The collective unconscious contains archetypes - universal themes such as the mother, hero, and self. Jung described personality types as introverted/extraverted with thinking, feeling, sensing, and intuiting functions. His method of analysis included dream analysis, word association tests, and active imagination to understand a patient's unconscious and facilitate self-realization through integrating opposing forces. Critics argue Jung's concepts are difficult to empirically test and some concepts lack clarity due to ambiguity.