A lot of the discussion about introversion and extraversion seems to collapse a whole bunch of things into a single binary. When people point out that they’re not well-described by either term, they tend to come up with patches like “ambivert,” but this is a missed opportunity to develop a more granular understanding of sociability. There are enough tensions in the underlying definitions that I want to blow up those terms and replace them with more precisely defined axes along which people vary:

• Stimulation affinity
• Social skill
• Social anxiety
• Relationship realism (vs intuitive individualism)
• Communalism (vs ideological individualism)

This isn’t a complete schema - it’s just a set of categories that might individually or together be useful in helping the user perceive finer distinctions than sociable vs unsociable.

Stimulation affinity

Some people seek out as much stimulation as they can. Others try to avoid it. Social interactions are a common source of stimulation, which is why this affects how much people seek out or try to avoid social interactions. Hans Eysenck, famously developed this definition of introversion and extraversion, where introverts avoid stimulation and extraverts seek it out.

If someone has a high stimulation affinity, they’ll tend to like interactions more than solitude, big gatherings more than small ones, raucous parties more than sedate conferences, and loud music and other kinds of stimulation, whether social or not. If someone has low stimulation affinity, they may need to take breaks to recover from all that stimulation, and find a lot of it draining rather than exciting.

Stimulation affinity might not even just be one thing - there are multiple possible reasons why people might like different amounts of stimulation, including:

• Reward response - Some people may have stronger reward-responses to stimulation than others.
• Stimulation threshold - Some people may have a higher threshold for what counts as stimulation than others, so they are both harder to satisfy and harder to overwhelm.

Reward response

Some people get a lot of pleasure out of food. They’re often willing to spend a substantial amount of time or money on obtaining the best culinary experiences, because they get a lot of value out of them. Other people don’t enjoy food very much - they might like it a little, and they might like better food more, but it doesn’t drive a large difference in enjoyment for them. These people are much less willing to spend effort on their food, at extremes preferring an all-Soylent or Mealsquares diet for a minimum of hassle.

Conceivably some people have a fully general lower reward response to stimulation (or to social stimulation). We should expect that in general these people will not be willing to expend as much effort on stimulation, even if it’s slightly pleasant. Depression sort of looks like an extreme version of this kind of state, where it’s not that particular things have lost their appeal, but rather that nothing seems good. (On the other hand, the comorbidity of depression and anxiety suggests that in some cases, depression might be due to an excess of (aversive) stimulation, in response to which part of the brain’s reward processing simply shut down in response to the overload.)

If the lack of reward is specific to social stimulation, then an unsociable person could become more sociably inclined by improving their social skills - in particular the ones related to perceiving social phenomena - or by finding a class of social interactions they like more than the ones currently available. If someone has a more general lack of affinity for stimulation, they might need to fiddle with their brain chemistry through a more general-purpose alteration like prescription drugs or therapy for depression.

On the other hand, someone who wants to be less reliant on / compulsive about social (or all) stimulation could cultivate patience through practices like meditation, or could find alternative sources of stimulation.

Stimulation threshold

Sometimes I’m lonely and want to be around people. Other times I feel socially overloaded and want to be alone. This makes sense if I’m implicitly trying to maintain some fixed level of stimulation, and feel distressed if things go too far in either direction.

On this hypothesis, introverts have a lower stimulation threshold, and pass their satiation point with less stimulation. This would explain the stereotype that introverts tend to be more reflective than extraverts: internal stimulation (e.g. thinking about stuff) is more salient to introverts, and more satisfying, leaving less appetite for external stimulation. By contrast, extraverts would need to amplify their thoughts by thinking out loud and through an external and preferably social process.

If someone who is typically above their stimulation satiation point wants more stimulation-seeking behavior, they could try removing unnecessary sources of stimulation for their lives, or training their brains to more efficiently process sensations by practicing graduated exposure. On the other hand, someone persistently below their stimulation satiation point might try cultivating more precise and subtle “mindful” awareness of their existing sources of stimulation.

Social skill

Some people have more interest in figuring out what’s going on socially than others do, or more ability to do so. People with more interest and ability end up handling social situations better, which gives them more access to more interactions. People with less end up alone more of the time, either voluntarily because their poor social skills make social interactions less pleasant for them relative to other ways they can spend their time, or involuntarily because other people don’t want to interact with them as much.

I suspect that this interacts in interesting ways with how we allocate our attention by default. People who find it easier to focus narrowly on the primary object of their attention are going to perceive social signals as distractions, which makes social processing worse both in the short run because they are allocating less attention to it and in the long run because they are learning less about it.

Social anxiety

Some people are timid or scared, either of interacting with people, or just in general. People with an anxious disposition may avoid all but the safest interactions - or, just, all of them. In addition, anxiety itself uses up energy that might otherwise be spent on interactions with other people.

Someone with social anxiety might be hypersensitive of what’s going on around them socially (and thus hyperaware of what might go wrong). Alternatively, their anxiety might cause them to be less socially skilled because they have less practice, or because they’re distracted by their anxiety. On the other hand, people who start out socially inept might develop an entirely reasonable fear of social interactions if too many of them go badly early on.

On the other hand, some people seem to have anxiety about being alone, and prefer the company of others in part because it helps their thoughts from drifting to unpleasant places.

Relationship realism vs intuitive individualism

Some people have a palpable experience of relationship. If they try to have a high-intimacy interaction with a stranger, something feels off. Their affordances for interacting with someone are based on their history together. Most people have at least a little bit of this - think of the first time you saw a schoolteacher or your doctor outside of their place of work. I call this disposition relationship realism, and people who have a lot of it, relationship realists.

It’s disorienting or scary for relationship realists to be around people without relating to them - so they try to build relationships, if only temporary ones, in order to build trust. This can make them seem very chatty to those without this preference. If they have a close relationship with someone, then it feels like something’s missing when the other person isn’t there.

By contrast, intuitive individualists don’t have intuitions for what relationships or community should be like, and don’t feel like something’s missing when it’s gone - they just know that there are a lot of people some of whom it’s good to interact with. As soon as they find a way to have a great interaction with someone, they're willing to jump in - and don't necessarily feel like they were taking a big risk or committing themselves to being closer in the future. Getting to know a person isn’t “building a relationship” for them the way it is for a relationship realist; it’s just learning about each other and establishing common knowledge about ways in which they can have good interactions.

Communalism vs ideological individualism

Some people feel like an important part of what makes their lives meaningful is the communal context in which they are embedded. These people will pay a lot of attention to what the people around them are doing, and will want input from them.

Other people feel like their autonomy is much more important. Someone who is highly attuned to social signals (a highly perceptive relationship realist), but holds personal autonomy as a value (an ideological individualist), will care a lot about being part of a community that highly values autonomy, because anything else will be a constant drag on their ability to be their authentic self.