Jung was one of the first people to define introversion and extraversion in a psychological context. In Jung's Psychological Types, he theorizes that each person falls into one of two categories, the introvert and the extravert. These two psychological types Jung compares to ancient archetypes, Apollo and Dionysus. The introvert is likened with Apollo, who shines light on understanding. The introvert is focused on the internal world of reflection, dreaming and vision. Thoughtful and insightful, the introvert can sometimes be uninterested in joining the activities of others. The extravert is associated with Dionysus, interested in joining the activities of the world. The extravert is focused on the outside world of objects, sensory perception and action. Energetic and lively, the extravert may lose their sense of self in the intoxication of Dionysian pursuits.[77] Jungian introversion and extraversion is quite different from the modern idea of introversion and extraversion.[78] Modern theories often stay true to behaviourist means of describing such a trait (sociability, talkativeness, assertiveness etc.) whereas Jungian introversion and extraversion is expressed as a perspective: introverts interpret the world subjectively, whereas extraverts interpret the world objectively.

“It is not that something different is seen, but that one sees differently. It is as though the spatial act of seeing were changed by a new dimension. —Carl Jung”