Psychological Types is found in volume 6 of The Collected Works of C. G. Jung.

Jung proposes four main functions of consciousness: two perceiving or non-rational functions (Sensation and Intuition), and two judging or rational functions (Thinking and Feeling). These functions are modified by two main attitude types: extraversion and introversion.

Jung proposes that the dominant function, along with the dominant attitude, characterizes consciousness, while its opposite is repressed and characterizes the unconscious. Based on this, the eight outstanding psychological types are: Extraverted sensation / Introverted sensation; Extraverted intuition / Introverted intuition; Extraverted thinking / Introverted thinking; and Extraverted feeling / Introverted feeling. Jung, as such, describes in detail the effects of tensions between the complexes associated with the dominant and inferior differentiating functions in highly and even extremely one-sided types.