Steven Pinker Gage Skidmore, via Wikimedia Commons, CC BY-SAI don’t know about you, but ever since I can remember – from my early teens – I have been bemused about the endless rituals we humans perform; and even more so about what can and can’t be said about these rituals, especially when the rituals involve obvious hypocrisies or are illogical.Review: When Everyone Knows That Everyone Knows: Common Knowledge and the Science of Harmony, Hypocrisy and Outrage – Steven Pinker (Allen Lane)Do you see what I just did with my opening paragraph?Obviously, through a brief personal reflection, I tried to give you a general sense of what much of Steven Pinker’s book When Everyone Knows That Everyone Knows is about: namely, that we often perform perplexing rituals for the sake of harmony, and if we draw attention to the quizzical aspects of those rituals – if we make these aspects common knowledge – we can get into trouble.But I also did something else. I started with the innocuous, “I don’t know about you…”Now hold on tight. This gets complicated very fast. Just like Pinker’s book.The thing is, I do believe that many people are bemused by the rituals we perform and the silences we must keep. But I wouldn’t say that this phenomenon is itself common knowledge. More accurately, I wouldn’t say that I know that you know that this is common knowledge. And I also wouldn’t say that I know that you know that I know that this is common knowledge. In drawing attention to this phenomenon, however, I am, like Pinker, helping to make this phenomenon, which involves common knowledge, common knowledge. I’m not joking. Well, actually, I am joking. But the joke is accurate. Pinker’s book goes on like this for hundreds of pages. Reading it is a discombobulating but glorious experience. Section after section takes us down one, then another, then another layer of reflexivity. In doing so, the book brings to light the endless ways that common knowledge – knowledge that everyone knows that everyone knows – affects our individual lives and society. Indeed, having read Pinker’s book, my sense is that tussling with “common knowledge” is just about the most common thing we humans do – it’s up there with breathing and sleeping. Though it isn’t exactly common knowledge that this is the case.What is ‘common knowledge’?Common knowledge is not exactly knowledge in the sense of established and widely accepted facts. Pinker is not talking about Einstein’s General Theory of Relativity or other well-established truths, like calculus or maybe even the law of supply and demand, though such truths do come into it. Rather, common knowledge refers to beliefs that are commonly held, and that people know to be commonly held. Sometimes these beliefs are true, sometimes not.The book begins with the classic example of Hans Christian Andersen’s story The Emperor’s New Clothes. Pinker writes: 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.And so the illusion could no longer be sustained. In this instance, the little boy’s speech was a threat to the status quo. It undermined the emperor’s prestige and revealed to everyone that, for the sake of something like harmony, they were upholding a ridiculous lie. Steven Pinker interprets the Emperor’s New Clothes as a story about common knowledge. Illustration by Vilhelm Pedersen (1849). Public domain, via Wikimedia Commons This account of common knowledge is useful. But Pinker’s immense insight concerns the way humans use common knowledge to coordinate action and bring about win-win situations. (Pinker, the great liberal optimist of our time, is drawn to win-win situations.) Humans have done remarkable things, and much of what we have achieved has been through cooperation: we work together to achieve common goods, which include not just survival, but progress. Given that each of us is a universe unto ourselves, a fundamental question is: how do we coordinate our cooperation? Pinker’s answer: using common knowledge. As he puts it:Life is filled with opportunities to coordinate with other people for mutual gain. We agree on a time and place to meet, bring complementary fare to a potluck dinner, divide responsibilities on a project.And yet,Coordination can fail if people are not on the same page, even when they want the same thing. Schedules clash, signals get crossed, and shared goals fall through the cracks. Ultimately, as Pinker writes, “our world is built on conventions that allow us to coordinate effectively and are self-reinforcing because they are common knowledge.”Common knowledge functioningPinker provides hundreds of examples of common knowledge at work, examples that often reveal its fragility and its double-edged nature. Here are a few.In many parts of the world, we all know that when traffic lights go red and there is a signal to walk, pedestrians can cross the road safely. This is common knowledge. Often in such situations, we will cross the road without even considering whether the cars will stop. But sometimes, when we are out and about, a car will stop to let us cross, even though the car has right of way. This works by the driver and pedestrian locking eyes and the driver giving a hand signal to cross. This establishes common knowledge between the two. It is also the case that the driver and pedestrian have the common knowledge that such situations often arise. And yet uncertainty lingers. We have all experienced this. As Pinker writes, I’m grateful for the courtesy and would like to cross, but I know he can’t wait forever, and I’m reluctant to step off the sidewalk in case he decides the time is up and he’s going to hit the gas.And so the hesitating and inching forwards and counter-waving begin. Turns out the common knowledge isn’t quite common. Another example involves relatively recent laws against smoking in public spaces. This example relies on the concept of a “focal point”. “Probably no one was ever arrested and convicted for smoking in a lecture hall or airport terminal,” Pinker writes. “But once NO SMOKING signs were posted, nonsmokers, who previously would not have wanted to create a scene, were emboldened to look daggers at the violators or ask them to stop, and they didn’t push back.”So common knowledge of a law, which likely isn’t enforced, and a humble sign, have transformed the air quality in many public places. This salutary example provides hope that more serious problems might, to some degree, be solved by optimising the coordination made possible by common knowledge. Pinker gives the example of nation states acceding to “agreements brokered by toothless mediators, courts, and religious leaders”. The point here is that even if international agreements are not enforceable in the same ways as domestic laws, these agreements can become focal points around which coordination can occur, such that win-win outcomes in the international realm become more possible. Steven Pinker argues that coordinated action depends on common knowledge. Christopher Michel, via Wikimedia Commons, CC BY-SA Common knowledge malfunctioningAn excellent example of common knowledge malfunctioning is a bank run. Because banks do not hold all the deposits of their customers, but lend them out to make a profit, banks can collapse if everyone tries to get their money back at once. Even a bank that is functioning well can collapse if enough people put enough weight on the fact that not everyone can get their money back. As Pinker observes, banks put considerable effort into suppressing this common knowledge, for example by making themselves seem like they have lots of money by having fancy interiors.Pinker also discusses how common knowledge is suppressed by authoritarian regimes. We see here a clear illustration of the importance of common knowledge for coordination. “The reason that citizens don’t resist their overlords en masse,” writes Pinker, “is that they lack the prerequisite to coordinating their behaviour for mutual benefit, namely common knowledge.” If everyone rebels at once, because there is sufficient confidence among the citizenry that everyone will rebel at once, a revolution can be successful. But so long as this confidence can be suppressed, the regime will endure. For me, one of the most interesting and dark functions of common knowledge relates to the lies people tell to bind a group together. This is not just about people being too nervous to say that the emperor has no clothes, or that the dictator is a dictator. It is about the necessity that the binding statement be a lie – or an “unverifiable belief”, as Pinker diplomatically puts it. Unverifiable beliefs are the best signals of commitment to the coalition’s norms: anyone can say that the sun rises in the east, but only a stalwart would affirm that Jesus is the son of God or that America is the greatest country on earth.I can think of many more examples.Cancellations and strategic silencesThis brings me to the part of the book that is closest to my own heart: cancel culture. (I had a book withdrawn from sale last year that spent a fair few words pointing out that the emperor has no clothes.) Pinker’s chapter “The Cancelling Instinct” begins by presenting numerous questions that have become taboo within universities over recent decades. These include: “Do women, on average, have a different profile of aptitudes and emotions than men?” “Did indigenous peoples frequently engage in war and genocide?” “Are there two sexes in animals, including humans?” “Is sudden-onset gender dysphoria in adolescent girls an effect of social contagion?” “Did European colonialism bring any benefits to colonized people, in addition to its harms?”The problem, as Pinker puts it, is that “people hold many factual beliefs not because the beliefs have been shown to be true but because they are felt to uphold a moral order”. This is clearly an issue within universities because, as Pinker rightly states, “societies entrust universities, at fantastic expense, with a mandate to discover and transmit knowledge”. People who ask difficult questions, people like the little boy who announced that the emperor had no clothes, are often silenced in one way or another because their questions risk generating a different common knowledge – one that will disrupt the moral status quo, upon which numerous careers and even lives depend.To finish, Pinker points out that it is far from clear that making something common knowledge is a good idea. Society, to function, depends upon strategic silences. Revealing truths, while generally desirable, is not always the endgame. Sometimes social cohesion is preferable. In fact, as Pinker says, “calling for complete honesty is the ultimate dishonesty. No one really wants it.” He quotes philosopher Blaise Pascal, who in 1670 wrote: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.When Everyone Knows That Everyone Knows is a challenging book. It is hard to navigate all of its depths. But this is also its point. The phenomenon of common knowledge is everywhere, and yet the way it functions is remarkably complex.Jamie Q. Roberts does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.