Introversion and extraversion were first set out systematically by Carl Jung in Psychological Types (1921). They describe whether a person's psychic energy and interest turn mainly inward, toward the subjective world, or outward, toward people and things. They are not the same as shyness or talkativeness. The MBTI is a later questionnaire built on Jung's ideas that sorts people into 16 types, but research has found real problems with its test-retest stability and validity. Most psychologists today measure introversion–extraversion with the Big Five trait of extraversion, a continuous dimension on which most people fall somewhere in the middle.
Key points
- Jung's introversion and extraversion are about where attention and interest flow, not about social skill.
- The MBTI was developed by Katharine Cook Briggs and Isabel Briggs Myers from Jung's theory, with an added judging–perceiving scale.
- Critics note that MBTI scores don't split into two peaks, so forcing people into either/or categories loses information, and in some early studies about half of people got a different type on retest a few weeks later.
- The Big Five treats extraversion as a continuous trait with finer facets such as sociability, assertiveness and energy level.
- Any type or score is a lens for looking at yourself, not a verdict.
Introversion and extraversion in Jung's Psychological Types
Jung published Psychologische Typen in 1921; the English text appears as Volume 6 of his Collected Works. He proposed two basic attitudes. In extraversion, psychic energy flows mainly toward outer objects, and a person is drawn and energized by people, events and surroundings. In introversion, energy returns mainly to the subject, and inner impressions, thoughts and feelings carry more weight.
Jung also described four functions, thinking, feeling, sensation and intuition, and discussed how they combine with the two attitudes. He stressed that pure types are rare: everyone has both attitudes, with different emphasis. In a later foreword he added that his typology was a tool for organizing psychological experience, not a way to label people at first sight.
By Jung's own meaning, then, an introverted person can be articulate and have many friends. They may simply recharge more through solitude and reflection and care most about what things mean to them.
How the MBTI grew out of Jung's theory
The Myers-Briggs Type Indicator was created by Katharine Cook Briggs and her daughter Isabel Briggs Myers, building on Jung. It describes people with four either/or scales: extraversion–introversion (E/I), sensing–intuition (S/N), thinking–feeling (T/F), and the judging–perceiving (J/P) scale they added. Combined, these give the familiar 16 four-letter types.
The MBTI is easy to remember, and for many people it's the first time they think seriously about how they differ from others. That explains its popularity. Being easy to use and measuring accurately are different questions, though.
The main research criticisms of the MBTI
Scores don't form two peaks. If people really came in E and I types, most scores would bunch at the two ends with few in the middle. Studies repeatedly find the opposite: scores are roughly continuous, with many people near the middle. McCrae and Costa (1989), analyzing 468 adults, found no support for truly dichotomous types. Two people whose scores differ only slightly can end up with opposite letters.
Limited test-retest stability. Pittenger's reviews (1993, 2005) summarize early studies in which roughly half of participants received a different four-letter type when retested after a few weeks. The publisher says newer versions have improved, but Stein and Swan (2019) note that such claims are hard to verify independently.
The theory is hard to test. Evaluating MBTI theory against standard criteria, Stein and Swan (2019) conclude that it fits poorly with established personality data, that core claims such as an inborn "true type" are hard to falsify, and that parts of the theory contradict each other.
These criticisms are about sorting people into fixed types. Feeling that a type description sounds like you isn't "wrong"; that feeling just isn't evidence that the test is reliable.
How the Big Five measures introversion and extraversion
The most widely used framework in personality research today is the Big Five: openness, conscientiousness, extraversion, agreeableness and neuroticism (negative emotionality). McCrae and Costa (1989) found that four MBTI scales line up with four Big Five traits. E/I tracks extraversion, S/N tracks openness, T/F tracks agreeableness, and J/P tracks conscientiousness. Neuroticism has essentially no MBTI counterpart.
The Big Five treats extraversion as a continuum. In the Big Five Inventory–2 (BFI-2) by Soto and John (2017), extraversion breaks into three facets: sociability, assertiveness and energy level. Someone can be low in sociability yet quite assertive at work. A single letter can't hold that detail.
Researchers have also tried to explain extraversion in terms of brain systems. DeYoung's (2015) Cybernetic Big Five Theory, for example, frames extraversion as engagement with and sensitivity to potential rewards and proposes links to dopamine-related systems. This is a theoretical framework still being tested; it doesn't mean "extraverts have one brain area that is more active."
FAQ
Does introverted mean shy or socially anxious?
No. Introversion describes energy and interest leaning toward the inner world, while shyness is more about nervousness in social situations. They can occur together or separately. If social anxiety is getting in the way of daily life, consider talking with a qualified professional.
Is the MBTI useless?
It can be a conversation starter and a prompt for self-reflection about differences between people. Because of its reliability and validity problems, it isn't suited to hiring, selection or drawing conclusions about someone.
Why do I get a different MBTI result each time?
This is common. Many people score near the middle on some scales, so small shifts in mood or context can flip a letter. That itself suggests personality is more like a spectrum than a set of boxes.
What is a more accurate way to understand my introversion or extraversion?
Look at research-validated Big Five measures such as the BFI-2. Even a well-built questionnaire describes statistical tendencies, not what you will do in any given moment.
Try it in SleepBeauty
SleepBeauty's Daily Quiz folds psychology research, Jungian ideas and a little brain science into a few light questions, such as whether tonight you feel more like reaching out or staying quiet. It won't hand you a fixed four-letter answer and it is not a diagnosis. It's a gentle way to notice how you are right now before sleep.
References
- Jung CG. Psychological Types. The Collected Works of C. G. Jung, Vol. 6. Translated by H. G. Baynes, revised by R. F. C. Hull. Princeton, NJ: Princeton University Press (Bollingen Series XX); 1971 (German original 1921). https://press.princeton.edu/books/hardcover/9780691097701/collected-works-of-c-g-jung-volume-6
- McCrae RR, Costa PT Jr. Reinterpreting the Myers-Briggs Type Indicator from the perspective of the five-factor model of personality. Journal of Personality. 1989;57(1):17–40. https://doi.org/10.1111/j.1467-6494.1989.tb00759.x
- Pittenger DJ. The utility of the Myers-Briggs Type Indicator. Review of Educational Research. 1993;63(4):467–488. https://doi.org/10.3102/00346543063004467
- Pittenger DJ. Cautionary comments regarding the Myers-Briggs Type Indicator. Consulting Psychology Journal: Practice and Research. 2005;57(3):210–221. https://doi.org/10.1037/1065-9293.57.3.210
- Stein R, Swan AB. Evaluating the validity of Myers-Briggs Type Indicator theory: A teaching tool and window into intuitive psychology. Social and Personality Psychology Compass. 2019;13(2):e12434. https://doi.org/10.1111/spc3.12434
- Soto CJ, John OP. The next Big Five Inventory (BFI-2): Developing and assessing a hierarchical model with 15 facets to enhance bandwidth, fidelity, and predictive power. Journal of Personality and Social Psychology. 2017;113(1):117–143. https://doi.org/10.1037/pspp0000096
- DeYoung CG. Cybernetic Big Five Theory. Journal of Research in Personality. 2015;56:33–58. https://doi.org/10.1016/j.jrp.2014.07.004