Steven Pinker on How Common Knowledge Rules Our Lives

0:00Welcome to another episode of Conversations with Coleman. This episode is a recording of a live conversation that I had at the Comedy Cellar in New York City with the great Steven Pinker. Steven is a Canadian-American cognitive psychologist, linguist, and popular science author. He's the Johnstone Family Professor of Psychology at Harvard University, and he previously taught at MIT and Stanford. Today, we're discussing his new book, When Everyone Knows That Everyone Knows. This book answers questions like, why did Biden's bad debate performance lead to his ouster when most Americans already believed he was too old?

0:36And also questions like, why do dictators hate comedy? Along the way, we also talk about U.S. foreign policy in general, where Stephen and I have some disagreements. We talk about how to apologize to people and when to apologize to people. And we even talk about read receipts. So without further ado, Stephen Pinker.

1:03Hey, Coleman here. If you're enjoying the show, then you probably care about how political decisions really get made. If that's you, I want to tell you about the new podcast, On Notice, produced by the nonpartisan newsroom Notice. Each week, journalist Reese Gorman sits down with lawmakers for candid conversations, not just about the headlines, but about what makes them tick and what brought them to Washington in the first place. On Notice gives you an insider's view of the people-shaping policy in the U.S. Reese's approachable style has earned him trust on both sides of the aisle, unlocking unguarded conversations that you won't hear in traditional interviews.

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1:53Okay, hello. How are we doing tonight? All right. So it's a very special occasion because there is a new Steven Pinker book. And I don't know about you, but every time there is a new Pinker book, I drop everything. I do a little dance in privacy that I'm going to spare you from right now. You definitely don't want to see it. but it makes me very happy that I'm able to share this moment with you and the book will be out next week and we're going to talk about it a bit today and we're going to touch some other topics so thank you so much for coming. First of all, Stephen, you've written about so many different topics.

2:31On any given day you could be writing about irregular verbs or the decline of violence around the world or the progress that human beings have made over the past 300 years or so, how does Steven Pinker pick a topic for his next book? Usually when, if I start to talk about something in conversation and I find people are intrigued, they want to know more, that is a cue that I have something to say that's worthy of a book. Also, sometimes I'll write a book and there'll be some question that I stumble upon that I realize I don't have enough room to pursue in that book or else it would go on forever.

3:17And so I know that that is also a good subject for the next book. Okay, so the subject of this book is common knowledge. And when most people think of the phrase common knowledge, you think of something that I know and something that you know. For instance, it's common knowledge that President Bush was the president of America in the early 2000s, right? That's not exactly the kind of common knowledge you're talking about. Explain what common knowledge is. It isn't. And common knowledge has come to take on a technical term meaning within game theory and philosophy and linguistics and economics.

3:54So it refers to the state in which I know something, you know it. 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 we're in a comedy club and people titter. It can be funny, and it actually has been the subject of plots and situation comedies, perhaps the best known being the episode of Friends where Rachel says to Joey, they don't know we know they know we know. Joey, you can't say anything. And he says, I couldn't even if I wanted to. which raises the puzzle of how could the concept of common knowledge, which, by the way, refers to that state of embedded knowledge about knowledge ad infinitum.

4:37Now, so immediately one has to ask, well, how could that be relevant to anything? Your head starts to hurt after two or three I knows that she knows, let alone an infinite number of them which can't fit inside a finite skull. But one of the reasons I took up the question is that as a cognitive psychologist, I was interested in how people can represent the state of common knowledge, if they do at all. There's reason to think that we do, because common knowledge is necessary for coordination. And that is why it has been of such interest among economists, philosophers, game theorists, coordination being the state in which two or more people make choices that benefit them both as long as they both make it.

5:20So there's no reason to drive on the right as opposed to driving on the left. but there's very good reason to drive on the same side that everyone else is driving on, whichever side that happens to be. And it's crucial that you know that everyone else knows that that's the side that you drive on. Or even something as simple as a rendezvous, to meet at a certain place. It's not enough to know that your friend likes to go to Starbucks, and so you go to Starbucks, because if he knows that you like to go to Pete's, he might then go to Pete's, and he might even think, well, wait a second, he knows I like to go to Starbucks, so he won't go to his favorite place.

5:57He'll go to my favorite place ad infinitum. Nothing short of common knowledge can guarantee that they'll end up at the same place at the same time. So how do we do it, given that technically it involves an infinite number of layers? I think if something is public, if it's conspicuous, if it's self-evident, if it's out there, if one of us sees it at the same time that we see someone else seeing it and they see us see it, that can generate common knowledge in one intuition. The intuition that's something, it's public, it's out there, you can't take it back, and that is psychologically the main way we experience common knowledge.

6:37So I came upon the concept when I was trying in a previous book, there's a case in which an open subject in one book leads to an entire other book. This is in my book, The Stuff of thought. I had a, whose subtitle was language as a window into human nature. One of the puzzles that I took up was long known to linguists, which is that a lot of the time, maybe most of the time, we don't say exactly what we mean in so many words. We, so for example, if you could pass the salt, that would be awesome. Now, that doesn't make a whole lot of sense if you took it literally, because, you know, not only would it not be worthy of awe, but why are you kind of entertaining counterfactual hypothetical possible worlds?

7:25Why don't people just say, give me the salt? Or, geez, officers, is there some way we could settle a ticket here without, like, going to court doing all that paperwork? I mean, we all know that that is a veiled bribe or want to come up for Netflix and chill. you know most people know that that isn't an invitation wait does that not mean Netflix and chill? I've been doing it wrong for a long time so they tell me so what's the difference? why don't we just you know kind of cut the crap and say what we mean and the difference between an innuendo where it's very very likely that your hero knows so there's no plausible deniability and just blurting it out.

8:12What's the difference? What I claimed was that blurting it out generates common knowledge. When you blurt it out, not only does your hero know what you have in mind, but they know that you know, and they know that you know that they know. And since social relationships, like a platonic friendship, like supervisor-supervisee, like transactional partners, are coordination games, they depend on common knowledge. When we don't want to challenge a relationship, will sometimes keep something out of common knowledge. It can be private knowledge, but it doesn't subvert the basis of the relationship. So I'm sorry, I've been going on at some length.

8:49I did write a whole book about this. Yeah. But that's how I came upon it, from an interest in language. Got it. So if I'm mind reading accurately, I can hear that some people are thinking, what the hell does this pretty interesting but wonky, nerdy concept actually have to do with real life? And because I've read your book and I've heard you talk about it elsewhere, I think there's an example that everyone can register, that can help people register its importance. I was commentating at CNN for the past, between like 2022 and 24, and I would notice every time the topic of Joe Biden's age came up, it seemed very obvious to me that Joe Biden was, like if he were my grandfather, we would be telling him you can't drive anymore and all this kind of stuff.

9:38And then not only that, I would look at the polls and it would say things like 60, 70 % of Americans believe Biden is too old to be president. And then when we would talk about it on TV, I would say, hey, maybe Biden's too old to be president. And everyone would say, what are you talking about? He's doing backflips in the White House. And then the interesting part is that Joe Biden's bad debate performance, to me, seemed like everything Joe Biden had been, it seemed identical to his performance over the past year. but something changed overnight. What is it that changed? No, it's a great example.

10:11And what changed was now there was common knowledge of what previously had been private knowledge. So indeed, polls showed that a large percentage of Americans thought that he was cognitively unfit to be president, but they didn't necessarily know that everyone else knew that. What happened during the debate, because it was something that was watched, not only was it watched by a large audience, but the large audience knew that it was a large audience. It was national TV. And then everyone realized it a stroke. Everyone knows what I privately knew. And indeed, the percentage of Americans who thought he was cognitively impaired, it did go up by a few percentage points, but only a few percentage points, because it was already a majority.

10:57But everything changed when it was now common knowledge. Again, there was a coordinated response, whereas previously there had been just scattered opinions. And in general, any highly public event has the capacity to generate common knowledge. The paradigm case in the way I begin the book is the story of the emperor's new clothes because when the little boy said the emperor was naked, he actually wasn't telling anyone anything they didn't already know. They could see the emperor was naked. So what changed? Well, at that moment, now everyone knew that everyone else knew that everyone else knew.

11:33And crucially, the common knowledge changed their relationship with the emperor from obsequious deference to ridicule and scorn. That is, it changed the relationship of authority, which like all relationships, I argue, is held in place by common knowledge and can be challenged by a change in common knowledge. Yeah, so to get why this is a profound concept, you really have to cement in your brain that 90 % of humans everywhere could know something, and it's still not common knowledge until suddenly they know that everyone else knows it. They know that they're in the majority, right? So that's the difference.

12:08I'm going to run some situations by you that might relate to common knowledge, and you tell me if you think they do. So when states are negotiating in like a sensitive behind-the-scenes negotiation. Think Arafat and Ehud Barak negotiating over Israel-Palestine in 2000. We know they're both so fearful of a leak. In other words, the prime minister of Israel might be currently negotiating that I'm going to give up this big thing that a lot of this painful concession, Arafat may think the same thing, but if it comes out that he's ready to give that out, he can no longer give it out. And it's a strange paradox because he, you know, if the deal were achieved, he would go home and say, we split Jerusalem in half, right?

12:59But if it leaks that he's about to split Jerusalem in half, he can't split Jerusalem in half. So does this relate to common knowledge in any way or is this something else? It's a great example. I haven't really thought it through, but it absolutely must. And I do talk about the fact that governance, and in fact any relationship depends on a certain amount of secrecy, one might even say hypocrisy. I think none of us would want there to be hidden microphones or telescreens with the Stasi eavesdropping our conversations at home, even though we're really not guilty of plotting anything. But you say a lot of things, even about your close friends, your boss, that you really would not want to be public because social relationships depend on common knowledge.

13:50Things that might be privately suspected are very different when they're out there, when they're leaked. So in the case of negotiations, probably what's driving that crucial difference is that broaching a concession is a sign of surrendering dominance or authority or face. That is, it's signaling weakness. It's signaling a willingness to back down in a confrontation. And confrontations are often resolved by the dominant one knowing that the subordinate one is going to back down, and the subordinate one backs down because he knows that the dominant one will hold his ground, which he knows because he knows the subordinate will back down ad infinitum.

14:36It's common knowledge who is the alpha and who is the beta. And a concession before it actually is consummated as a deal can be seen, especially among people in the same coalition, as a willingness to surrender dominance, to lose face, to back down, and therefore to have forfeited an advantageous negotiating stance in the future. Next question, are you an alpha or a beta? I'm kidding, don't answer that. So over the past few years, I can't remember when I first heard this term, but I'm sure many will be familiar with the term dog whistling. It's the idea that a political commentator or someone on cable news is saying something that's kind of a coded message to his particular base, but is meant to sound innocent enough for the rest of the world to not realize, wink-wink what he's getting at, which group he's talking about, and so forth.

15:36Does this have to do with common knowledge at all? Yeah, it does. It is a way of avoiding common knowledge. And it can even be that if the dog whistle is recognized as a dog whistle, it can still be more effective than just blurting something out. Because again, what can be widely distributed private knowledge, or at least private with specific to one group, not common across groups, can then maintain the relationship of status or face saving between them. So even if you highly suspect that it's a dog whistle, there can still be a different psychological status than if it's blurted out overtly.

16:22Then if you accept it without challenging it, without confronting the person, you haven't surrendered your bargaining position. Okay, another example might be political apologies. I think there's this interesting dance any time a politician does something wrong or something that many people think is wrong that some people will say, well, why don't you just apologize? Just acknowledge you messed up and people will forgive you. But I think a lot of politicians have the instinct that if I apologize, that will actually somehow make it worse. And could this possibly have to do with common knowledge?

17:00Because an apology is sort of like a recognition that everyone knows that everyone knows that it's wrong rather than it being sort of up for debate, even if most people did think it was wrong. Yeah, so apology has a different function when you talk. In one of the chapters in the book, I categorize human relationships into three broad types, drawing on a theory from the anthropologist Alan Fisk, who did a cross-cultural survey. There's communal sharing or communality. We're all brothers. What's mine is thine. Share and share alike. There's authority. Don't mess with me. And then there's reciprocity or equity.

17:42Tit for tat, even Stephen trading. We're very psychologically attuned to what relationship we have. I think an apology in the context of a communal relationship, a couple or a friendship, can cement the relationship. It means that you don't have grounds for defecting when someone has tried to claim an unfair advantage. You don't bail out. If they apologize, they've given some clue that they know that they have messed up or taken advantage of you, and they won't do so in the future. So you have reason not to bail. in a relationship of dominance if that's what the leader is trying to reinforce apology can be a loss of face an inability to stand his ground in the future with the confidence that the other person will give way and I think that's when you get into the situation of was it Admiral Nelson who said never apologize never explain bad advice if you're in a relationship, if you're in a marriage Contra the old cliche from the movie Love Story, love means never having to say you're sorry That's not very good advice for a romantic relationship Okay Are read receipts You know what read receipts are?

19:09Yes Are read receipts an example of common knowledge and what does it mean when you turn on your read receipts with someone as opposed to not having them on? Yeah, there was actually reproduced an ad for the now defunct BlackBerry smartphone. And the caption was, you'll know, they know, you know, they read it. I actually find rather terrifying. That is, the read receipt was the default as opposed to something you request. That was supposed to be an advantage. Maybe that explains why they went out of business. But yeah, there is a big difference. And there's a famous theorem in the literature on common knowledge that actually no number of read receipts suffice to guarantee coordination compared to being on the same page having the synchronous conversation.

20:04Because you could always wonder, they got the read receipt, but did they know that you know that they got the read receipt? You have to send a read receipt for the read receipt. and one of the reasons that the definition of common knowledge is that it has to be an infinite number of layers of I know that he knows is that no finite number of read receipts actually establishes the coordination with certainty. I remember the example from the book to make that more concrete it's like you and I are generals with different factions in an army we know we can beat these guys but only if we attack together so I send you a message saying I'll attack if you attack and you say okay I'm ready to attack but I don't know if you've gotten the message yet right and then you send me a message and you don't know if I've gotten the message that you've gotten the message that I've gotten the message and so we never have the confidence to strike unless you have something like cell phones or simultaneous communication right.

20:58That's exactly right and it is a famous theorem and it was originally called the electronic mail game to refer to kind of read receipts for electronic mail also called the coordinated attack problem. I think it does have manifest, it has a lot of manifestations, why sometimes it's so hard to say goodbye, like you hang up first. No, you hang up first. No, you hang up first. She hung up on me. Or if you're pedestrian and you're stepping on the, and a car stops, not at a red light, but courtesy to let you pass, and you don't know whether you should go or because the, for all you know, the driver might think you've decided not to go, and so then he'll gun.

21:41He might think, well, you've decided to let him pass, which is why I reproduced a sign that I saw in San Francisco Airport. It says, at the zebra crossing, it says, make eye contact with the driver. And eye contact is a quintessential common knowledge generator 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. ad infinitum implicitly. And so eye contact, it's a potent signal. In this case, of just mere coordination. We agree, pedestrian can cross, car will stop. But eye contact is also a potent generator of common knowledge. It's as in, can you look me straight in the eye and say that?

22:28Or the barroom taunt, you looking at me? My colleague, my late colleague at Harvard, Irvin DeVore, the anthropologist, used to tell his introductory behavioral biology class, if two humans anywhere on the planet look into each other's eyes for six seconds or longer, then either they're going to have sex or one's going to kill the other one. So eye contact doesn't have a suit. I actually try that with my class. And after five seconds, I say, stop, stop.

23:03But in the pedestrian crossing case, it's merely to coordinate a simple plan, but hardwired into us, because eye contact is also a threat signal in other species, in many primates, and in canines as well, that it can have a hardwired function as well. In humans, it's more generic. It's something that has hitherto been private knowledge is heretofore common knowledge. That's why eye contact is so potent. And it's one of a number of nonverbal signals that I deal with in one chapter of the book called laughing, crying, staring, blushing, staring, glaring, displays that I argue are common knowledge generators.

23:52Namely, they are potent because the expressor feels them from the inside at the same time as he's displaying them from the outside, knowing that the perceiver knows that he's experiencing it from the inside. Again, ad infinitum. But in one fell swoop. I'm blushing right now. You just can't tell. Okay, so let's talk about how common knowledge relates to authoritarian regimes. So you talk about in the book how, you know, we're thinking of places like North Korea, Cuba, Venezuela, and, you know, the Soviet Union under Stalin, were places where it can be just like, you know, 70, 80 % of the population can be dissatisfied.

24:37And if they all rose up together, they'd be able to topple the regime, but it cannot happen for, you know, 50, 100 years. So how does that relate to common knowledge? Yeah, there's a, I quote a line from the movie Gandhi, where the Gandhi character says to a British officer, in the end, you will leave because there is no way that 100 ,000 Englishmen can control 350 million Indians if the Indians refuse to cooperate. He could have said refuse to coordinate because indeed 350 million Indians can overpower a regime of 100 ,000 colonial officers if they all stand up at the same time and refuse to work or storm the palace.

25:17The problem being, how do they coordinate given that common knowledge is necessary for coordination? Well, that's why dictators try to prevent common knowledge. It explains why they censor, why they clamp down on public demonstrations, because a widely circulated article or even slogan generates common knowledge. If everyone knows it, everyone hears it. Now can be the time that everyone stands up at once, whereas individually, they might be afraid of being picked off one by So it's why freedom of assembly is considered a fundamental right in a democracy and why dictatorships forbid public rallies, likewise a public dissemination of information.

26:08I reproduce a joke from the Soviet Union in which a man is distributing leaflets in Red Square. And of course, the KGB arrest him, take him back to headquarters, only to discover that the leaflets are blank sheets of paper. So they confront him. They say, what is the meaning of this? He says, what's there to say? It's so obvious. Now, the point of the joke is he was generating common knowledge. That is, he didn't have to say anything. The mere fact that he was distributing it, that people were accepting it, meant that people now knew that they were not the only ones disgruntled with the regime.

26:46Moreover, that even if everyone suspected that everyone else was disgruntled, until they had grounds for believing that everyone knew that everyone else knew, they would not have the confidence or the coordination to oppose the regime in unison. And in a case of life imitating a joke, a few years ago, Putin's forces arrested a man for holding a blank sign, as if they had heard the joke. And along those lines, there was a very interesting and counterintuitive fact about the Chinese Communist Party and the way they do censorship in your book. Yes, from my colleague Gary King, who did a study, managed to infiltrate hundreds of thousands of social media posts and which ones were censored by the Chinese government.

27:37And it turned out it was not complaints against the regime. In fact, they used those as kind of inside intel as to which of the commissars wasn't doing his job at kind of placating the masses. But what they did stomp on was any attempt to coordinate. People having a meeting, sharing information, sharing news about a new bulletin board, anything that would allow people to get together is what they came down on like a ton of bricks. Right. So they actually want real private feedbacks to avoid people getting disgruntled. They just don't want people to meet in the town square. Exactly. Or the electronic equivalent.

28:15Right. So if you think about the Arab Spring in 2011, where you basically have one Arab country rises in revolution, demands democracy, and then all these other Arab countries follow suit in short order, is this an example of common knowledge and salience? Yeah, it is. And it all, one of the remarkable things about the Arab Spring is that it all began on what would seem like a rather isolated incident, a Tunisian fruit peddler who was harassed by the authorities and set himself on fire in protest. That started a chain of events that led to regime change in a variety of countries, and then eventually to one of the worst civil wars in the 21st century, the Syrian civil war.