Think of a dreadful secret about yourself, something shameful that nobody knows. Now imagine someone close to you stumbles across the horrible truth and you don’t know they know; they’ve kept it to themselves. From your perspective that relationship is completely normal. Yet if you find out that they know, and they find out that you know they know, everything changes. The secret hasn’t altered, nor has the number of people exposed to it. What’s different is the knowledge about that knowledge. It was private, and now it’s common knowledge, public to both of you. And that makes all the difference.
This is Steven Pinker’s 12th book. The first two were academic works on his area of expertise, language and cognition, subjects he’s researched and taught at Harvard for many years. These were followed by a string of popular bestsellers – The Language Instinct, How the Mind Works, The Blank Slate.
In 2011, he took a turn towards the political with The Better Angels of our Nature, a controversial interdisciplinary argument that pre-modern, pre-industrial societies were significantly more violent than most people imagined, and that moderns enjoy long, safe lives thanks to government, commerce and expanding moral norms. He’s advanced his pro-modernity position in Enlightenment Now and Rationality, which made a doomed attempt to teach the world to think clearly. Four years and one Trump re-election later, we have When Everyone Knows That Everyone Knows.
For Pinker, common knowledge is a social technology that allows complex societies to solve co-ordination problems and align our behaviours and norms across large and diverse populations. But it can also malfunction, leading to speculative financial bubbles, mobs and moral panics. In this framework, rationalism isn’t a problem of individual thinking; it’s the success or failure of a society to curate its systems of common knowledge.
Money is the most conspicuous example of the advantages and flaws of this practice. It began as a store of value, but now it has no physical existence at all. Wealth is completely notional – entries in databases, validated purely by the social convention that we’ll all agree to acknowledge it. It’s not possible to have private wealth. A database with a trillion dollars of your own currency that only you consider valuable is worthless. Bubbles and financial panics manifest as failures of this common knowledge. If everyone “knows” that prices in a market (tulip bulbs, mortgage derivatives, residential properties in Auckland) will increase, everyone pours their money in; when everyone knows prices are overvalued, the bubble bursts and the market collapses.
Say you’re in Paris and you and a friend have to rendezvous tomorrow – your lives depend on it! – but you have no agreed place or time and no way to communicate. You’ll almost certainly go to the Eiffel Tower at midday, and your friend will probably do the same. This is known as a focal point, first described by the economist Thomas Schelling, who pointed out that the human ability to co-ordinate our behaviour by anticipating each other’s knowledge and choices then acting accordingly, is a computational task of mind-blowing complexity – yet we perform it effortlessly. Once we start looking for focal points in human behaviour we find them everywhere: in language, non-verbal signals (what are tears and laughter but mechanisms for making our private states public?), dress codes, public rituals – marriages and funerals are tools to make significant events a form of common knowledge – laws, punishments, property rights.
“Pluralistic ignorance” is one of the pathologies of common knowledge. It’s possible for a group to land on a focal point they all disagree with as individuals but concede to the public consensus. Everyone remembers a class in school they didn’t understand but failed to ask questions about on the assumption everyone else followed along. Employees believe new policies are foolish but obey them because they think everyone else approves. When the Berlin Wall fell, it emerged that most East Germans hated their government but thought everyone else supported it. The collapse of the wall created a new form of public knowledge allowing everyone to re-co-ordinate. The perils of these “spirals of silence” are that they can be self-reinforcing. The more people stay quiet, the stronger the appearance of consensus.
There’s a double-edged quality to this social tool. It enables extraordinary levels of co-operation and co-ordination, but triggers panic, empowers mobs and entrenches untruths.
Pinker endorses free speech as a solution to these problems, good liberal that he is. Even false or bad ideas should be made public. Rituals and institutions that seem arbitrary or old fashioned are often a focal point creating some form of common knowledge, helping people co-ordinate fairly and predictably: you should probably leave them in place. But we should be more aware of these informational mechanisms in case they are malfunctioning and causing harm.
It’s ironic that awareness of common knowledge isn’t very common but has largely been the province of a handful of social psychologists, economists and game theorists. However, as we shift to global forms of communication that allow its pathologies to mutate and proliferate, perhaps it’s important for more people to know about what everyone does and doesn’t know.
