Extraversion and introversion
Extraversion and introversion are a central trait dimension in human personality theory. The terms were introduced into psychology by Carl Jung, though both the popular understanding and current psychological usage are not the same as Jung's original concept. Extraversion is typically associated with sociability, talkativeness, and high energy, while introversion is linked to introspection, reserve, and a preference for solitary activities. Jung defined introversion as an "attitude-type characterised by orientation in life through subjective psychic contents", and extraversion as "an attitude-type characterised by concentration of interest on the external object".
While often presented as opposite ends of a single continuum, many personality theorists, such as Carl Jung, have suggested that most individuals possesses elements of both traits, with one being more dominant. Virtually all comprehensive models of personality include these concepts in various forms. Examples include the Big Five model, Jung's analytical psychology, Hans Eysenck's three-factor model, Raymond Cattell's 16 personality factors, the Minnesota Multiphasic Personality Inventory, and the Myers–Briggs Type Indicator.
History
Experimental Foundation.The quantitative foundation of Jung's typology lies in his early research at the Burghölzli Hospital. Through the Word Association Experiment, Swiss psychiatrist Carl Jung provided the first empirical evidence of "complexes." He observed that individuals showed distinct patterns in how they responded to emotional disturbances: some subjects were consistently oriented toward the objective meaning of the stimulus, while others were derailed by internal, subjective associations.
Clinical Observation.
Jung observed a fundamental divergence in how psychic energy moved in psychiatric patients. He noted that in Hysteria, energy flowed outward toward the object, whereas in Dementia Praecox, it withdrew into a subjective inner world. By 1913, Jung concluded that these were not merely symptoms of illness but exaggerated manifestations of normal psychological orientations. Longitudinal Introspection and the Four Functions.
The differentiation of the four psychological functions emerged from Jung’s period of intense self-experimentation between 1913 and 1917, now known as his "confrontation with the unconscious." Documented in The Red Book, Jung utilized the method of active imagination to observe the autonomous behavior of his own mental processes. This longitudinal introspection allowed him to map how certain functions dominate consciousness while their opposites remain "inferior" and unconscious. By comparing these personal findings with the case histories of his patients, Jung moved from a simple two-fold model to the complex eight-fold functional system published in 1921. While the terms 'introversion' and 'extraversion' had prior use in European thought, Jung was the first to integrate them into a comprehensive structural theory of personality. He redefined these concepts not merely as social traits, but as fundamental directions of psychic energy, establishing the first systematic model of psychological types based on the movement of psychic energy libido toward the subject or the object.
In his seminal work Psychological Types, Jung synthesized years of clinical observations and experimental research to propose that personality is structured by the movement of psychic energy. He identified two primary 'attitudinal types'—introvert and extrovert—not as rigid classifications, but as dynamic orientations of the libido toward either the inner subjective world or the outer objective reality. Jung compares these two psychological types to ancient archetypes: Apollo and Dionysus. The introvert is likened to Apollo, who shines a 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.
Jung believed that the differences between extraverts and introverts are typically apparent even to laymen: 'Even in a circle of friends and acquaintances the psychological layman will have no difficulty in distinguishing two groups of individuals, the one characterized by an open, frank and genial nature, who are easily reconciled to a given situation, and form attachments with ease... while the other group is characterized by a withdrawn, often inscrutable nature, and a certain shyness...' "
Jung's original concepts of introversion and extraversion differ fundamentally from their common usage in modern trait psychology. While contemporary models, such as the Big Five, often define these terms through social behavioral traits, Jung defined them as 'directional orientations of libido.' In Jungian theory, the distinction lies in the movement of psychic energy: whether an individual's primary value and interest are directed toward the inner subjective world or the outer objective reality. The modern misunderstanding of these terms is largely attributed to later psychometric adaptations, most notably by Hans Eysenck. While Eysenck adopted Jung's terminology for his PEN model, he stripped the concepts of their psychodynamic depth, redefining extraversion primarily through sociability and impulsivity—traits that Jung considered merely secondary effects. Unlike Jung’s model, which focused on the subjective-objective flow of energy, Eysenck’s behavioral approach turned introversion-extraversion into a static, temperament-based scale measured by outward social conduct.
Modern theories often stay true to behaviourist means of describing such a trait, whereas Jungian introversion and extraversion are expressed as a perspective: introverts interpret the world subjectively, whereas extraverts interpret the world objectively. For the extravert, the libido flows outwards, and the person has an interest, relationship and dependence on events, people and things. As such, the extravert is very influenced by her environment. By contrast, the introvert's libido flows inwards towards subjective factors, and is influenced by 'inner necessity'.
In September 1909, Carl Jung used the term introverted in a lecture at Clark University. A transcript of this lecture was then published with two others in a journal in 1910, the first time the term appeared in print. In the lecture he mentions that love that is "introverted... is turned inward into the subject and there produces increased imaginative activity".
His 1921 book Psychologische Typen was published as Psychological Types in English in 1923. It described the "introverted" in detail for the first time. In his later paper, "Psychologische Typologie", he gives a more concise definition of the introverted type, writing:
He holds aloof from external happenings, does not join in, has a distinct dislike of society as soon as he finds himself among too many people. In a large gathering he feels lonely and lost. The more crowded it is, the greater becomes his resistance. He is not in the least "with it," and has no love of enthusiastic get-togethers. He is not a good mixer. What he does, he does in his own way, barricading himself against influences from outside. He is apt to appear awkward, often seeming inhibited, and it frequently happens that, by a certain brusqueness of manner, or by his glum unapproachability, or some kind of malapropism, he causes unwitting offence to people...
For him self-communings are a pleasure. His own world is a safe harbor, a carefully tended and walled-in garden, closed to the public and hidden from prying eyes. His own company is the best. He feels at home in his world, where the only changes are made by himself. His best work is done with his own resources, on his own initiative, and in his own way...
Crowds, majority views, public opinion, popular enthusiasm never convince him of anything, but mere make him creep still deeper into his shell.
His relations with other people become warm only when safety is guaranteed, and when he can lay aside his defensive distrust. All too often he cannot, and consequently the number of friends and acquaintances is very restricted.
In the 1950s, British psychologist Hans Eysenck theorized that the trait of introversion-extraversion could be explained in terms of Clark Hull's drive theory of motivation. He later developed his own arousal theory to explain individual differences in the trait, suggesting that the brains of extraverts were chronically under-aroused, leading them to seek out stimulation from the environment. Introverts, being more cortically aroused, avoid overstimulating environments. The trait of introversion-extraversion would become one of three central traits in Eysenck's PEN theory of personality.