Ask most people whether they’re an introvert or an extravert and you’ll get a fast answer, usually with a small note of relief, as if they’ve just told you their blood type.

Introvert: quiet, drained by parties, happiest with a book. Extravert: loud, energized by crowds, first to the microphone. Two boxes. Pick one and file yourself away.

The strange thing is that the man who gave psychology those two words never meant them as boxes. Carl Jung, the Swiss psychiatrist who brought “introversion” and “extraversion” into psychology in his 1921 book Psychological Types, was pointing at something looser and stranger than a personality label. He saw them not as who you are, but as something you do. That framing might make your own tendencies feel less like a life sentence.

A quick note before we go further: I’m not a psychologist or clinician, and this is a piece of reading and reflection on a century-old idea and the research that followed it, not personal advice. Jung’s claims here are his theory, and the modern findings I mention are broad patterns across many people, not verdicts about you.

What Jung actually claimed

In his own words, Jung called introversion and extraversion “not characters at all, but mechanisms, which can, as it were, be inserted or disconnected at will” (other translations render the phrase “switched on or off at will”), as one survey of his typology records — not what you are, but what you do, and can stop doing.

For Jung, these are two directions your mental energy can flow: outward, toward people and the world, or inward, toward your own inner life. Everyone has both. He wrote that “everyone possesses both mechanisms, extraversion as well as introversion, and only the relative predominance of one or the other determines the type.” A quiet person isn’t missing the outward gear. They just spend less time in it.

That’s a real shift in how to hear the label. The everyday version treats “introvert” as an identity. Jung treated it as a setting that happens to be running most of the time.

How a setting hardens into a type

So where does the “type” come from, if it isn’t baked in? Jung’s answer is habit.

He proposed that “one mechanism will naturally predominate, and if this condition becomes in any way chronic a type will be produced.” The key word is chronic. One setting runs, then keeps running, then becomes the default, and eventually you call that default your character.

My read is that the character isn’t the cause, it’s the residue. You don’t withdraw into yourself because you’re an introvert. Over years of habitually turning inward, “introvert” becomes a fair description of the pattern. Jung even allowed that your surroundings, not just inborn disposition, shape which mechanism ends up in charge. The type forms over time, not at birth.

That’s a more honest picture than the boxes, because it leaves room for the obvious fact that people behave differently in different rooms. The same person can be the quietest one at a work meeting and the loudest at a small dinner. On the box model that’s a contradiction. On Jung’s model it’s just two settings, used as the situation asks.

Where modern science agrees, and where it doesn’t

A century on, personality researchers still argue about how much of this holds up, and the answer is a real mix. Today’s leading framework, the Big Five, treats extraversion as a stable trait that shows up fairly consistently across situations and over time. That’s closer to the “box” than to Jung’s freely switchable mechanism. Researchers also estimate the Big Five traits are roughly 40 to 60 percent heritable, meaning a good chunk is inherited. There is something durable here, not just habit.

But on one big point the science lands close to Jung. Almost nobody sits at the extremes. Personality researcher Jens Asendorpf estimates that “ninety percent of people are somewhere in the middle” of the range between extravert and introvert. That’s a rounded estimate, not a hard count, but the picture is clear. Introversion and extraversion sit on a smooth scale, and most of us cluster near the center. People in that middle band are often called ambiverts.

Where does one category stop and the next begin? Mostly it doesn’t. As psychologist Scott Barry Kaufman puts it, “there is no magic line that clearly separates ambiversion from introversion and extroversion.” The lines we draw are conveniences, not natural borders.

There’s even a case that the middle is a good place to be. Adam Grant’s study of 340 call-center salespeople found the top earners weren’t the outgoing extraverts everyone pictures behind a sales desk. Over three months, people with “intermediate extraversion” brought in about 24 percent more revenue than strong introverts and 32 percent more than strong extraverts. One study in one workplace, so I wouldn’t build a life around it. But it fits the pattern: the extremes aren’t the sweet spot. Kaufman also argues there’s “no hierarchy of goodness when it comes to personality traits,” adding that each has its advantages depending on the situation.

Holding the idea without over-labeling

Where the science parts ways with Jung is on the “at will” part. You probably can’t flip your dominant orientation on command the way you flip a light. It’s stickier than that, and it tends to shift slowly with age rather than by choice. A large review of 152 long-term studies found personality traits grow more stable as we get older, reaching their highest consistency only after around age 50. Movement is real, but gradual.

Still, the useful thing to take from Jung isn’t the “switch at will” claim. It’s the reframe underneath it. If “introvert” names a habit rather than a cage, then it describes what you’ve tended to do, not the outer wall of what you can do. That’s a lighter thing to carry than an identity. It also makes you slower to pin the label on other people, whose quiet at your dinner table might just be the wrong room for their louder setting.

So the next time you reach for the box, reach a little more carefully. You’re someone with two mechanisms and a well-worn preference — and that preference describes where you’ve tended to go, not where you can go.