The Hidden Rules Holding Society Together: Steven Pinker on Common Knowledge

Science of Perception Box

In this episode of Science of Perception Box, cognitive scientist Steven Pinker explores the concept of 'common knowledge'—not just what everyone knows, but

Key takeaways

• Common knowledge is not just shared information but a recursive awareness: I know you know that I know, and so on.
• Coordination in social life—like driving or flirting—depends on common knowledge to avoid miscommunication.

Main topics

• Common knowledge in philosophy and game theory
• Social coordination through shared understanding

Notable quotes

"Common knowledge is necessary for coordination—like driving on the right or left. It doesn't matter which side you drive on, but everyone must know that everyone else knows."

Conclusion

Common knowledge is a foundational yet invisible force in human society, enabling cooperation, maintaining

Transcript preview

Speaker 1 (0:00) So why can't people be completely honest? Speaker 4 (0:02) Complete honesty, which is common knowledge. You know what the other person knows what you're saying and they know that and you know that. I can threaten the nature of Speaker 2 (0:11) a Speaker 4 (0:11) relationship. Speaker 2 (0:12) Hi, I'm Elizabeth Koch. What's a perception box? It's this invisible mental box that each one of us lives inside, built from the material of our beliefs, life experiences, and the meaning we've made out of those experiences. You could think of it as a kind of reality filter that's constantly shaping how we see ourselves, other people, and the world around us. This podcast explores how, although the walls of this box are always present, they can expand in moments of curiosity, awe, and wonder, or contract in response to fear, anxiety, and anger. In each episode, we invite experts to share how to create lasting shifts in our perception. I'd like to introduce our esteemed host, Heather Berlin, professor of psychiatry and neuroscience at the Icahn School of Medicine at Mount Sinai, and Christophe Koch, chief scientist for the Tiny Blue Dot Foundation and former president of the Allen Institute for Brain Science. Welcome to the Science of Perception Box. This week, our guest is Dr. Steven Pinker. We tend to think that communication is about saying what we mean, but much of it is guessing what others know, assume, expect, or intend. Steven's work shows how much of our social world depends on this and how easily things break down when those interpretations don't align. This episode reminds us that even in ordinary moments, we're not just communicating, we're navigating each other's perception boxes. Speaker 1 (1:46) So first we want to open up with our own stories. So Christoph, has there ever been an interaction that you've had where, you know, you've realized after the fact that you were in the dark about some common knowledge, like everybody else knew, but you didn't know? So Speaker 3 (2:03) as you probably know, I don't own a car and a bike everywhere. And of course, as a biker, you have to be incredibly attuned to the laws and the customs of interaction between cars and bikes. You know, you have to look at the nods. Is the car giving me a nod so I can pass in front of it or I can enter the lane? So far, this has all worked out. But recently, a couple of months ago, I had this incident where there was another biker who came into my lane. And I thought he had given me the signal to proceed. by nodding. And I accepted that by nodding back, but he didn't get that. So I knew that he knew that I knew, but he didn't, he didn't close that loop. And so we ran into each other as a consequence of not fully completing the acknowledgement of the acknowledgement. Speaker 1 (2:52) That's a great example. So, well, welcome to the podcast. Thank you. Can you define common knowledge? Common Speaker 4 (2:59) knowledge in the... Technical sense from philosophy and game theory refers to the case where I know something, you know something, I know that you know it, you know that I know it, I know that you know that I know that you know it, ad infinitum. So common knowledge in the technical sense is interesting because it's necessary for coordination, for people to be on the same page. to do things that may be arbitrary, but are advantageous if everyone does it the same way. So driving on the right versus the left, stopping at a red light, these are all paradigm cases, excellent examples. It actually doesn't matter whether you drive on the right or the left. It does matter that everyone drives on the same side and that everyone knows that everyone else is driving on the same side. And so in general, traffic works. In England, everyone does it on the left, and here we do it, everyone does it on the right. works out fine, is often in cases where there isn't common knowledge, where you get failures to coordinate, as in Christoph's example of failure to establish common knowledge between a cyclist and a motorist. That often happens when there isn't some public signal that each one sees, knowing that the other one sees it, such as a traffic light, such as a zebra crossing, such as a stop sign. The reason that they are there is to establish these conventions that work by common knowledge. If I see the stop sign, I know that everyone else sees the stop sign, and we all know that that's the place to stop. But Speaker 3 (4:26) looking as people can replace that. Indeed. Partially, right? Speaker 4 (4:30) Partially, yes. The relevance to social relations is that I suggest that our relationships are situations of coordination. Coordination games in the sense of game theory. That just as... Driving on the right works because everyone knows that everyone knows that you drive on the right. You and I are friends because, you know, not because we signed a contract that, you know, stipulates our responsibilities, because, you know, I know that we're friends and you know that we're friends and I know that you know and you know that I know and so on. Or, alternatively, relations of deference. The person who is kind of higher on the status hierarchy stands his ground because he knows that they... The beta will give way, the beta gives way because he knows the alpha will stand his ground, et cetera, et cetera, et cetera. Or transactional relationships or romantic relationships. That suggests that each one of those is a coordination game and that they are ratified or upended by certain common knowledge generators, signals that each one perceives knowing that the other one is perceiving it too. Language being the most efficient way of generating. common knowledge. So in the case of, Christoph mentioned that eye contact can often generate common knowledge. That is, eye contact we know, even from the ethological literature in animal communication, is a very potent signal because you're looking at the part of the person that's looking at the part of you that's looking at the part of them that's looking at the part of you. And so eye contact can generate common knowledge. It often resolves these ambiguities in, say, a car. stopping and a pedestrian crossing, establishing eye contact would be a way of generating that common knowledge. Speaker 3 (6:11) Or two people or two cars merging on a freeway. The other guy just sort of briefly nods. Exactly. And Speaker 4 (6:17) in fact, I was tickled to see a sign in San Francisco airport parking lot, which actually... photographed and included in the book. And it has a cartoon of a pedestrian and a driver and a dashed line joining their eyes. And it says, make eye contact before crossing. Speaker 1 (6:35) There Speaker 4 (6:35) it is. Yes. Speaker 1 (6:36) That's great. But in a way, Speaker 4 (6:38) I Speaker 1 (6:38) mean, this common knowledge is a way to have, you know, what you're saying, you know, why it's important. It's for social, it's for coordination among groups of people. But what happens when you know, people get it wrong. You know, I'm thinking about, you know, when you all pull up to a four-way stop and nobody knows where to go and you're both waving to go. But I mean, that's a smaller example. But like, is there, are there disagreements? I think, you know, you know something that you might think I know something different or we don't agree on what is common knowledge. Oh, Speaker 4 (7:09) you bet. And the, in the traffic case, it could lead to a collision. That's the ultimate miscoordination. in social interactions can lead to the situation we call awkwardness, or if it is deliberate and protracted outrage. For example, if two people have a platonic relationship and one would say to the other, hey, do you want to have sex? That could be really awkward, which is why we have the phenomena of euphemism and innuendo. Do you want to come up and watch my Netflix? Or Netflix, yes. And I suggest that all of the rituals of genteel hypocrisy, politeness, consist in avoiding the common knowledge that might threaten a relationship while still slipping the information in. The idea is that there's private knowledge, there could even be reciprocal knowledge, but not necessarily the common knowledge that would threaten the relationship. So just to be more... concrete. If he says, do you want Speaker 3 (8:14) to Speaker 4 (8:14) come up for Netflix and show? And she says, no. I mean, she's a grown-up. She knows what come up for Netflix and show means. So she knows what he intended. And he's a grown-up. He knows that she knows. But does he know that she knows that he knows? And does she know that he knows that she knows? Deniability, right? Well, it's not even so much the deniability of the proposition, because again, she's no fool. But he could always say, Speaker 3 (8:39) oh, I just meant watching a movie. I didn't intend anything else. Well, I think Speaker 4 (8:42) it's the deniability of the common knowledge. That is, she could plausibly think, well, maybe he thinks I'm naive. Maybe he thinks that it went over my head. And he could think, well, maybe she thinks I'm dense and I don't realize that she knows that I know. And that higher order deniability allows them to preserve the relationship of platonic friends or colleagues or... come up with an even more fraught situation, supervisor and supervisee, whereas blurting out, do you want to have sex? Violates. Direct speech generates common knowledge. That common knowledge would contradict the tacit understanding of the platonic friendship or the collegial relationship. I couldn't go back to the... So you can't go Speaker 3 (9:28) back. To the relation Speaker 4 (9:29) I had before. Exactly. And again, because common knowledge is what cements. particular kinds of relationships and direct speech generates common knowledge. Innuendo, euphemism, politeness leads to private knowledge, but not common knowledge. You can maintain the fiction of a photonic friendship. As Speaker 1 (9:52) a therapist, I'm advising people on relationships and I'm often telling them, be open, be honest, tell a person how you really feel. But that's not always- But probably not Speaker 4 (10:02) everyone. No. Sometimes, yeah. Speaker 1 (10:04) I Speaker 4 (10:04) mean, no. And clearly, so therapy, especially couples therapy, marital counseling, family counseling, consist of encouraging people to make something common knowledge that was previously private knowledge in the case that there was something dysfunctional about that equilibrium, about the relationship that they'd been locked into. But in other circumstances... if the equilibrium is working out, you're best off not saying everything that's on your mind. This is what we call, we have names for this, knowing when to keep things out of common knowledge. We call it tact, savoir-faire, social skill. That's what social skill often consists of. It's the ordinary civility that we try to implement in human relationships. I mean, a simple example is just ordinary politeness. If you could pass the salt, that would be great. Now, literally, that doesn't make a whole lot of sense. It's counterfactual, hypothetical. Why are you musing about possible worlds at the dinner table? But