Read: 2025-10-11
Recommend: 8/10
Protesting with blank paper in China during COVID echoes tactics used in the Soviet Union, as people use various methods to create or avoid common knowledge.
Here are some text that I highlighted in the book:
When the little boy said the emperor was naked, he wasn’t telling anyone anything they didn’t already know. But he added to their knowledge nonetheless. By blurting out what every onlooker could see within earshot of the others, he ensured that they now knew that everyone else knew what they knew, that everyone knew that everyone knew that, and so on. And that changed their relationship to the emperor, from obsequious deference to ridicule and scorn.
One of the best jokes from the vein of subversive humor in the Soviet Union has a man standing in the Moscow train station handing out leaflets to passersby. Soon enough the KGB arrest him, only to discover that the leaflets are blank sheets of paper. “What is the meaning of this?” they demand. The man replies, “What is there to write? It’s so obvious!” The point of the joke is that the pamphleteer was generating common knowledge. Everyone knew that the Communist regime was inefficient and oppressive, but they could not have been sure that everyone else had come to that conclusion. A man in a public place calling attention to the existence of reasons for discontent was making that discontent known, and the awareness of it known, even if he didn’t need to make the reasons themselves known.
After all, one could imagine that dictators would allow their powerless subjects to bitch and moan all they wanted. Political power, wrote Mao Zedong, “grows out of the barrel of a gun.” In reality there is an excellent reason why dictators brook no dissent. The immiserated subjects of a tyrannical regime are not deluded into thinking that they are happy. And if tens of millions of disaffected citizens act together, no regime on earth has the brute force to resist them. The reason that citizens don’t resist their overlords en masse is that they lack the prerequisite to coordinating their behavior for mutual benefit, namely common knowledge. Most citizens may be concealing their political opinions to avoid being punished, with the result that no one knows that a majority of their compatriots share their disgruntlement. They might even mistakenly think that everyone else is loyal to the regime—a combination of private knowledge and common misconception known as pluralistic ignorance, or a spiral of silence.
Dictators’ attempts to quash common knowledge have in turn inspired activists to think up ever more creative means of generating it, often by baiting the government to criminalize innocuous activities. The stunts include clapping hands, singing songs, opening umbrellas, wearing buckets on their heads, baring their breasts, setting their cell phones to ring simultaneously, tying flags to the tails of stray cats, performing sword fights, or frying eggs and sausages on the eternal flame of a war monument. (A satirical notice in Belarus reported, “A kindergarten teacher has been found guilty of fomenting disorder for teaching her charges how to play pattycake.”35) And in a case of life imitating a joke, in 2022 Russian police arrested a woman for, yes, holding a blank sign. A common saying in the Soviet era, sometimes attributed to Aleksandr Solzhenitsyn, was “We know they are lying. They know they are lying. They know that we know they are lying. We know that they know that we know they are lying. And still they continue to lie.” Perhaps they continued to lie because even three levels of mutual knowledge stopped short of the common knowledge that would have allowed the people to coordinate a challenge to the lies.
“It’s out there” and “You can’t take it back” are two of many idioms for common knowledge that refer to something in plain sight or public earshot. Here are some others: The cat is out of the bag. It’s on the record. The insult was in his face. She spilled the beans. It’s best if we bring this into the open. For years he was in the closet, but he finally came out. Let’s put this on the table. The bell can’t be unrung.
When people wish to avoid common knowledge, the conceptual metaphor can be adapted to refer to efforts to avoid seeing things that are in plain sight: The emperor has no clothes. She chose to look the other way. He buried his head in the sand. Don’t go there. That’s the elephant in the room. This includes awkward moments when one person enters a fact into common knowledge and the other may prefer to keep it out.
A defendant was on trial for murder. There was strong evidence indicating his guilt, but there was no corpse. In his closing statement, the defense attorney resorted to a trick. “Ladies and gentlemen of the jury,” he said. “I have a surprise for you all—within one minute, the person presumed dead will walk into this courtroom.” He looked toward the courtroom door. The jurors, stunned, all looked eagerly. A minute passed. Nothing happened. Finally the lawyer said, “Actually, I made up the business about the dead man walking in. But you all looked at the door with anticipation. I therefore put it to you that there is reasonable doubt in this case as to whether anyone was killed, and I must insist that you return a verdict of ‘not guilty.’ ” The jury retired to deliberate. A few minutes later, they returned and pronounced a verdict of “guilty.” “But how could you do that?” bellowed the lawyer. “You must have had some doubt. I saw all of you stare at the door.” The jury foreman replied, “Oh, we looked, but your client didn’t.”
Two mathematicians arguing at a whiteboard often will flip sides as they struggle for clarity, each passionately arguing for the conclusion that they had passionately argued against just moments before. It’s a display of an epistemic virtue called active open-mindedness, of treating beliefs as “hypotheses to be tested, not treasures to be guarded.” As the economist John Maynard Keynes did not in fact say but often gets credit for saying, “When the facts change, I change my mind. What do you do, sir?”
The incongruity of anonymous donors earning esteem for their anonymity is just one example of a social paradox, a term suggested by the psychologist David Pinsof for phenomena like these: We try to gain status by not caring about status. We rebel against conformity in the same way as everyone else. We show humility to prove we’re better than other people. We don’t care what people think, and we want them to think this. We make anonymous donations to get credit for not caring about getting credit. We bravely defy social norms so that people will praise us. We avoid being manipulative to get people to do what we want them to do. We compete to be less competitive than our rivals. We help those in need, regardless of self-interest, because being seen as the type of person who helps those in need, regardless of self-interest, is in our self-interest. We make subversive art that only high-status people appreciate. We make fun of ourselves for being uncool to prove we’re cool. We self-righteously defend false beliefs to prove we care more about the truth than virtue-signaling. We help our friends without expecting anything in return, because we know they would do the same for us. We show everyone our true, authentic self—not who society wants us to be—because that is who society wants us to be.
The only sane rationale for possessing nuclear weapons is deterrence against an all-out attack, and many strategic analysts have concluded that a country could accomplish that with a few dozen missiles in concealed submarines. No one can explain why the world needs more than twelve thousand nuclear warheads—as an American admiral put it, “You seldom see a cowboy, even in the movies, wearing three guns. Two is enough.” But during the eighty years that nuclear weapons have been around, nine countries have accumulated these threats to humanity’s existence because they served as status symbols, or displays of resolve, or gestures of reassurance to allies, or moves of tit-for-tat matching or gap-closing or besting or keeping up with the Joneses.
A major goal of cognitive behavioral therapy is to get patients to learn to identify what’s eating them.
Whether or not the eyes are a window to the soul, they certainly are a window to the mind. Our eyeballs are in constant motion to extract detail from the spot in the visual world most relevant to our current interests, so when people follow our gaze they are reading our mind. And when the gaze they follow is gazing back at them, they are reading the mind of a mind reader. Eye contact is the ultimate common-knowledge generator: we are seeing the part of the person that sees us seeing them seeing us. Eye contact is not uniquely human, but it must have been uniquely important in the evolution of our species, because we are designed to flaunt the direction of our gaze. Our black pupil and colorful iris are set off by a contrasting white sclera, unique among primates, and they are framed in an oblong window, also distinctively human. It all fits: eye contact generates common knowledge; common knowledge is necessary for coordination; humans are consummate coordinators. Not surprisingly, eye contact is a major choreographer of human social life.
It turns out that “eye contact” in everyday social interaction is a bit of a misnomer. It’s not just the five-second rule. What people call “eye contact” in conversation is not a pupil-to-pupil straight line. Our eyes dart all over our interlocutors’ faces, spending the most time on the bridge of the nose and often dipping down to read their lips. Come to think of it, we can’t look each other in the eye, because each of us has two of them. Parallel rays from eyeball to eyeball would mean that we were staring through each other into infinity, not peering into each other’s souls. Meaningful, sustained eye contact means choosing one eye to stare into, then jumping to the other one, a switch we don’t even notice. Try looking at one eye in your reflection in a mirror, then the other. It’s as if nothing happened. You are blind during the eye movement, and looking into either eye feels like looking into both. Hollywood directors know this, and tell actors in a love scene to switch eyes every few seconds.
Each time, he looked the maître d’ in the eye, taking care not to glance down at the fifty in his hand, and came up with a line such as one of these: “I hope you can fit us in.” “I was wondering if you might have a cancellation.” “Is there any way you could speed up my wait? “We were wondering if you had a table for two.” “This is a really important night for me.” To his astonishment, it worked every time—he was seated within two to four minutes.
Of course, governments, corporations, and the media can be even more punitive. Repression of speech is more the rule than the exception in human affairs. Over the course of history, occasional defenses of free speech pop out from a backdrop of persecution for blasphemy, heresy, or lèse majesté. And censorship and punishment of speech remains the norm in vast swaths of the globe today, including Russia, China, and most of Africa and the Middle East. I’m focusing on the drive by academics to censor one another both because of its timeliness and because it stands in such stark contrast to the professed values of a university in a liberal democracy. Why does repressing speech come so naturally to people that it bleeds through even in institutions dedicated to the exchange of ideas?
It also reminds us of the preciousness of privacy in the lives of individuals. Totalitarian states in fiction, like Nineteen Eighty-Four, and in reality, like communist East Germany and China, tolerate no zone of privacy, obliterating them with electronic surveillance and networks of anonymous informants. The rationale is, If you aren’t doing anything wrong, what do you have to hide? But of course even the most innocent of us has a great deal to hide. We know our relationships and reputations would lie in smithereens if the convivial conversations we enjoy with friends and intimates, with all their mordant remarks and politically incorrect wisecracks, were ever made public. Again, this would appear to be a part of the human condition. As Blaise Pascal put it in 1670, “I lay it down as a fact that if all men knew what others say of them, there would not be four friends in the world.”
The historical trend toward openness has a natural limit, with radical honesty turning out to be the greatest hypocrisy of all. People need to keep many thoughts private, however illogical that might appear at first glance. It’s easy to “explain” this diffidence by appealing to common sense: we’re naturally sensitive and inhibited and polite, and want to avoid offending people or causing tension and embarrassment and awkwardness and bad feelings. All true, but too glib to be a satisfying explanation. Why did evolution equip us with these feelings, rather than a willingness to let it all hang out? The logic of coordination and common knowledge applied to social relationships, as I have explained it in this book, provides an answer. Humans are not independent monads bouncing around like molecules in an ideal gas. The evolutionary niche of Homo sapiens is one of massive interdependence. Some of this working together is altruistic cooperation, where I’ll scratch your back if you scratch mine, but much of it is mutualistic coordination, in which one hand washes the other. Life presents us with many stag hunts, coffee dates, dollars to divide, collisions to avoid, groups to organize, fights to avert, and other positive-sum games. All require common knowledge so that each player is sure the other opts for the same win–win equilibrium. That includes our informal social relationships, which are held together by a compact of conventions. The conventions are idealizations, verging on fictions. Yet in a strict logical sense they are necessary for the coordination equilibria we enjoy, and undermining them with contrary indications can poison that coordination. We often keep the knowledge that would undermine a social convention private, not because of some uptight fuddy-duddy inhibition, but for rational, indeed mathematically provable, reasons.
Communal sharing is based on the fiction that everyone is an equal member of a collective in which each unstintingly sacrifices toward the good of the whole. It’s a lovely model, and it may be true as far as it goes, but it goes only so far. The overlap of interests that natural selection builds into families is only partial, with siblings competing over parental investment, parents pulled in different directions by their current and future children, and couples divided by loyalty toward blood kin and by opportunities for infidelity. And when everyone contributes to a common pot, some have the opportunity to stint, hoard, or hog. These ever-present realities contradict the commonly held conventions that make the warmth of communality possible, and it’s natural that they be kept out of common knowledge (while being understood privately so that people can protect themselves from exploitation).
A rational understanding of hypocrisy, grounded in the idea that common knowledge enables coordination, can stop us from ruining our personal lives with runaway candor. It can also prevent us from jettisoning some of the hypocrisies in public life that may seem obsolete but serve a real purpose. The police often choose to look away from infractions that the offenders try to veil, however thinly, such as “escort services,” drug paraphernalia advertised as tobacco accessories, and public drinking from a whiskey bottle in a paper bag. Enforcing the letter of every law would be exorbitant and intrusive, but allowing it to be common knowledge that laws may be openly flouted would signal that the legal system has forfeited its authority.
In the international arena, the fate of the world may depend on what is kept out of common knowledge. Israel’s policy of “deliberate ambiguity,” neither affirming nor denying that it has nuclear weapons, furnishes the deterrent value that makes possession worthwhile without provoking its Middle Eastern rivals to acquire their own to save face. Taiwan is patently a sovereign state, and the United States and the European Union unofficially treat it that way while officially denying that it exists. The reason for the duplicity is that publicly acknowledging the reality would be an affront to the People’s Republic of China, which has staked its reputation on being the sole ruler of all of historic China. The history of violence sparked by communal outrages reminds us that symbolic affronts can have catastrophic consequences. In all these cases, the people who maintain the hypocrisy could explain why they are maintaining it, but may choose not to undermine the rationale by stating the explanation in so many words. They may resort to euphemism and discreet omission, and in doing so they are far from being irrational. In a similar way, if scholars tacitly decide that the best way to handle a socially pernicious and intellectually minor topic is not to go there, they would not be surrendering to the ignorance of a dark age, but may be deploying a higher-order rationality which factors in the effects of making discoveries common knowledge. That could even be true if they reasoned that the best way of implementing such a policy is not to speak too long and loud about why they are implementing it.
All these trains of thought are exercises of recursive mentalizing, the cognitive talent that underlies common knowledge. The power of cognition to take its own outputs and feed them back into more cognition is a theme that has run through all my books, and it fills me with awe even after decades of pondering human intelligence. It underlies the vast expressive power of language, its ability to convey ideas from nursery rhymes to metaphysics. It explains how human intelligence, having evolved to reason about survival and reproduction, can be extended to reason about science, philosophy, and mathematics. It explains how human progress is possible, when people rethink their norms and institutions. And it implies that rationality itself is limitless: even when an application of rationality is flawed, we can step back, rationally analyze how we are deploying our rationality, and devise a higher-order rationality that subsumes it. It’s what’s most special about our kind: we not only have thoughts, but have thoughts about our thoughts, and thoughts about our thoughts about our thoughts.