What Makes Something a Convention? (And Why That Matters)

Imagine you and a friend agree to meet after school. You can’t text each other, and you forgot to pick a place. You both just have to guess. If you both go to the library, great. If you both go to the soccer field, also great. But if you go to the library and your friend goes to the soccer field, you waste an afternoon wandering around alone.

Now imagine that this happens every day. Somehow, over time, you and your friend start showing up at the same place. Maybe it’s the library. Maybe it’s the soccer field. It doesn’t really matter which one—what matters is that you both go to the same one. After a while, you don’t even think about it. You just go. And if a new kid joins your group, they’ll learn: “Oh, we meet at the library.” They’ll go there because everyone else does.

This is what philosophers call a convention. It’s a pattern of behavior that a group follows, not because it’s the only possible way to do things, but because everyone else is doing it, and it’s better for everyone if they all do the same thing.

But here’s where it gets weird: how do conventions start? How do they spread? And are they just about practical things like where to meet, or do they creep into deeper stuff—like what money is worth, what words mean, and even what counts as true?

The Problem with “Everyone Just Agreed”

At first, you might think: conventions are just agreements. People sat down and decided. But that can’t be right for most conventions. Nobody ever held a meeting to decide that everyone in the United States should drive on the right side of the road. It just sort of happened. And if you go back far enough in history, nobody ever held a meeting to decide what the word “dog” means.

David Hume, a Scottish philosopher from the 1700s, noticed this problem. He pointed out that languages and money systems developed “by human conventions without any explicit promise.” Think about that: nobody signed a contract saying that a dollar bill is worth something. Nobody voted on what the word “justice” means. Yet we all act as if these things are real.

Hume gave a famous example: two men rowing a boat together. They don’t need to talk or make a deal. They just figure out how to row in sync. Each person rows because the other person is rowing, and they both want to get where they’re going. That’s a convention in action.

So the big puzzle is: how do conventions arise without anyone explicitly creating them?

David Lewis’s Big Idea: Coordination Problems

About 200 years after Hume, a philosopher named David Lewis (who was just 28 when he wrote his book on this) gave a really precise answer. Lewis said conventions are solutions to coordination problems.

A coordination problem is a situation where:

There are at least two ways to do something.
Everyone involved wants to do the same thing, but nobody much cares which thing.
You can’t communicate in advance to decide.

Lewis’s favorite example was the telephone game—the real kind, not the party game. Imagine two people talking on the phone, and they get disconnected. Who should call back? The problem is that each person would prefer that the other person call back (to avoid paying for the call). But both prefer talking to not talking. So if both call back at once, they get busy signals. If both wait, nobody calls. The only way to solve it is for everyone to follow a rule: “If we get disconnected, the person who originally called calls back.” Or: “If we get disconnected, the person who received the call calls back.” Either rule works, as long as everyone follows the same one.

Lewis said that a convention has four key features:

Everyone actually follows it. (In real life, close enough counts.)
Everyone expects everyone else to follow it.
Everyone prefers to follow it, as long as almost everyone else does.
There’s at least one other possible convention that would also work. This is the “arbitrariness” part—conventions could have been different.

This last point is important. The fact that we drive on the right in the US isn’t because the right side is naturally better. It’s just a convention. Other countries drive on the left and get along fine. What matters is that we all do the same thing.

But Wait—Are Conventions Always About Coordination?

Some philosophers think Lewis’s definition is too narrow. They point to things that feel like conventions but don’t seem to solve coordination problems.

Take fashion. Is there a convention about wearing black to funerals? Sure. But does this solve a coordination problem? Not really. I don’t particularly care what other people wear to a funeral, and they don’t care what I wear. Yet there’s still a convention.

Or take the rules of chess. The rule that bishops move diagonally isn’t a solution to a coordination problem with other players. It’s just a rule that defines the game. The philosopher Andrei Marmor calls these constitutive conventions—they don’t just coordinate behavior; they actually create the activity itself. Without the rules, there is no chess.

Some philosophers, like Margaret Gilbert, argue that conventions are even more social and binding than Lewis thought. For Gilbert, a convention involves a kind of joint commitment. When you’re part of a convention, you’re not just doing what’s convenient. You’re part of a “we”—a group that has accepted a rule together, even if nobody said it out loud. That’s why breaking a convention feels wrong, even if it’s just a minor social rule. You’ve violated a commitment.

The Normativity Problem: Why Should I Follow a Convention?

Here’s a puzzle that keeps philosophers up at night. Conventions seem to have a kind of “should” attached to them. If there’s a convention in your family to take off your shoes at the door, you should take off your shoes. But what kind of “should” is that?

It’s not a moral “should”—nobody thinks you’re a bad person if you track mud inside. It’s not exactly a practical “should” either—maybe you’re comfortable wearing shoes. There’s something in between, a kind of social normativity that philosophers still argue about.

Lewis had a partial answer: if everyone else is following the convention, you have a practical reason to follow it too, because you’ll be worse off if you don’t. (If everyone else drives on the right and you drive on the left, you crash.) But this doesn’t explain why we feel a sense of obligation about small things like thank-you notes or table manners.

The Really Controversial Part: Are Truth and Logic Conventions?

Now we get to the part that makes some philosophers nervous. Starting in the early 1900s, a group called the logical positivists argued that even logic and mathematics are just conventions. The idea was that sentences like “All bachelors are unmarried” are true because of the way we define words. And maybe mathematical truths like “2 + 2 = 4” are similar—they’re true because we’ve set up our symbols and rules that way.

The philosopher Rudolf Carnap took this very far. He said we can choose different “linguistic frameworks” for doing science. We could pick a framework with numbers, or one without. We could pick classical logic, or a different logic. The choice is just based on convenience, not on any deeper truth. There’s no “right” answer outside of whatever framework we pick.

This idea—that even the most basic truths might be up to us—was exciting, but it ran into a serious problem. Another philosopher, W.V.O. Quine, argued that you can’t really have “truth by convention” all the way down. Why? Because to apply a convention, you already need logic. You can’t set up the rules of logic using logic itself—that would be like trying to lift yourself by your own bootstraps.

Quine also pointed out something simpler: why bother saying that the truth of “Everything is identical to itself” is due to convention? It’s true because everything is identical to itself. The convention just gives us words to say it. The truth itself isn’t conventional.

Most philosophers today think Quine had a point. You can’t make everything conventional, because you need some basic rules to even have conventions at all. But the debate isn’t settled, and some philosophers still defend versions of conventionalism about logic.

Is Language a Convention?

This is probably the most fought-over question in the whole debate. Everyone agrees that specific words are arbitrary—there’s no reason “dog” means dog except that English speakers use it that way. But is the whole system of language based on convention?

David Lewis thought yes. He said that using a language involves a convention of truthfulness and trust: speakers try to say true things, and listeners trust that speakers are telling the truth. This convention keeps itself going because it’s useful for communication.

But critics point out that people lie all the time. Is it really a convention if it’s broken so often? And even if we do usually tell the truth, does everyone have a good reason to? If I want to deceive you, I have a reason to break the convention, not follow it.

The philosopher Donald Davidson went even further. He argued that convention isn’t the foundation of language—it’s the other way around. You need language first to have conventions, because conventions involve things like promises, agreements, and shared understanding, which all presuppose language. So you can’t explain language in terms of convention without going in a circle.

This is a deep disagreement that hasn’t been resolved. Some philosophers think language is fundamentally conventional; others think it’s more like a natural ability, with conventions only playing a supporting role.

How Do Conventions Actually Get Started?

Assuming conventions aren’t made by explicit agreements, how do they arise? Lewis talked about salience—one option “stands out” for some reason, and people converge on it. In his famous example, he asked people: you’re supposed to meet a friend in New York City tomorrow, but you can’t communicate. Where do you go? Most people said “noon at Grand Central Station.” Not because there’s a rule, but because it’s the most obvious choice.

Other philosophers use evolutionary game theory to model how conventions develop. Imagine a population where people randomly try different behaviors. Some behaviors work better than others. Over time, the successful behaviors spread. Eventually, everyone settles on one way of doing things—not because anyone planned it, but because it was the most stable pattern.

Brian Skyrms, a contemporary philosopher, has shown how signaling systems (like early language) can evolve this way. In computer simulations, agents start off just making random noises and random responses. But over many rounds of interaction, they converge on stable patterns where certain signals reliably cause certain responses. No one designed the system. It just emerged.

Why This Still Matters

Conventions are everywhere, and they shape almost everything we do. The value of money, the meaning of words, the rules of games, the norms of politeness, the structure of property—all of these are, at least partly, conventional. But understanding how they work, and how much is really just convention, is surprisingly hard.

The big questions remain:

Can we change conventions if we want to? If money is just a convention, could we invent a different system?
Are there limits to what convention can create? Can we make something true just by agreeing to treat it as true?
When should we follow a convention, and when should we break it?

These aren’t just academic questions. People argue about them every day—in politics, in law, in school, in families. Every time someone says “that’s just the way things are done,” they’re appealing to convention. And every time someone asks “why?”, they’re questioning it.

That’s what philosophy does: it looks at things we take for granted and asks whether they really have to be that way.

Appendices

Key Terms

Term	What it does in the debate
Convention	A pattern of behavior that a group follows, where there are alternatives and people conform because others do
Coordination problem	A situation where people need to match their actions, and there’s more than one way to do it successfully
Salience	The quality of “standing out” that helps people converge on one convention without communicating
Constitutive convention	A rule that doesn’t just regulate behavior but actually creates the activity (like chess rules)
Joint commitment	Gilbert’s idea that conventions involve a shared “we” who have accepted a rule together
Truth by convention	The controversial idea that even basic truths (like logical truths) are true because we set them up that way
Nash equilibrium	A stable state in a game where no one can improve their outcome by changing their own strategy alone
Common knowledge	Something that everyone knows, everyone knows that everyone knows, and so on, infinitely

Key People

David Hume (1711–1776): Scottish philosopher who first analyzed conventions as arising without explicit agreements, using the example of two people rowing a boat together. He argued that property, justice, and money are all conventions.
David Lewis (1941–2001): American philosopher who gave the most influential modern analysis of convention using game theory and coordination problems. He was 28 when he wrote his book on the topic.
Rudolf Carnap (1891–1970): German philosopher who argued that even logic and mathematics are just linguistic conventions we choose for convenience. He sparked a huge debate about “truth by convention.”
W.V.O. Quine (1908–2000): American philosopher who attacked Carnap’s conventionalism, arguing that you can’t have logic itself be a convention because you need logic to apply conventions.
Margaret Gilbert (born 1942): Contemporary philosopher who argues that conventions involve “joint commitment” and create a “plural subject”—a sense of “we” that Lewis’s account misses.
Donald Davidson (1917–2003): American philosopher who argued that convention is not the foundation of language; rather, language is needed for conventions to exist.

Things to Think About

If money is just a convention, what happens when people stop believing in it? Does it still have value? Can you think of a time when this actually happened?
Gilbert says conventions involve a kind of commitment, even if nobody said anything. Is that true? If you move to a new country and don’t know the local conventions, are you really breaking a commitment, or just making a mistake?
Quine’s argument against “truth by convention” seems to show that you can’t make everything conventional. But how do you decide where the line is? What must be non-conventional for conventions to work?
Davidson says you need language to have conventions. But then how did language start? Isn’t that exactly the kind of thing that arises without agreement, like a convention?

Where This Shows Up

In school: Class rules, grading systems, and even the schedule of the school day are conventions. They could be different, but they work because everyone follows them.
In video games and sports: The rules of any game are conventions. They’re arbitrary (you could change them), but they create the game. When a new game comes out, players have to learn the conventions to play together.
In arguments about fairness: When people argue about whether something is “fair,” they’re often arguing about which conventions to follow—or whether to change them.
In science: Scientists use conventional systems of measurement (meters, grams) and classification (what counts as a planet). These conventions affect what they discover.