Carl Jung was a Swiss psychiatrist and psychoanalyst who founded analytical psychology. Jung's work was influential in the fields of psychiatry, anthropology, archaeology, literature, philosophy, and religious studies. Jung worked as a research scientist at the famous Burghölzli hospital, under Eugen Bleuler. During this time, he came to the attention of Sigmund Freud, the founder of psychoanalysis. The two men conducted a lengthy correspondence and collaborated, for a while, on a joint vision of human psychology.
Freud saw the younger Jung as the heir he had been seeking to take forward his "new science" of psychoanalysis and to this end secured his appointment as President of his newly founded International Psychoanalytical Association. Jung's research and personal vision, however, made it impossible for him to bend to his older colleague's doctrine, and a schism became inevitable. This division was personally painful for Jung, and it was to have historic repercussions lasting well into the modern day.
Among the central concepts of analytical psychology is individuation—the lifelong psychological process of differentiation of the self out of each individual's conscious and unconscious elements. Jung considered it to be the main task of human development. He created some of the best known psychological concepts, including synchronicity, archetypal phenomena, the collective unconscious, the psychological complex, and extraversion and introversion.
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.[82] Jungian introversion and extraversion is quite different from the modern idea of introversion and extraversion.
Modern theories often stay true to behaviourist means of describing such a trait (sociability, talkativeness, assertiveness etc.)