In this classic work, originally published in 1921, Jung categorized people into primary types of psychological function. He proposed four main functions of consciousness: Two perceiving functions: Sensation and Intuition Two judging functions: Thinking and Feeling The functions are modified by two main attitude types: extraversion and introversion. Jung theorized that the dominant function characterizes consciousness, while its opposite is repressed and characterizes unconscious behavior. The eight psychological types are as follows: Extraverted sensation Introverted sensation Extraverted intuition Introverted intuition Extraverted thinking Introverted thinking Extraverted feeling Introverted feeling In "Psychological Types, " Jung 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.