What I know you know...: Steven Pinker chats about how common knowledge has shaped our world

How have the unsaid understandings between people moulded us - our society, history, culture? In his new book, the Harvard psychologist digs for answers.

We laugh at the same jokes (usually for the same reasons), blush at innuendo, bow to dictators (at least temporarily), all because of a sense of implicit understanding: ie, common knowledge. We maintain social contracts such as friendships and kinship, and group together as mobs, based on common knowledge too.

Photo by Eric Haynes

The idea of common knowledge is key to understanding human social constructs, says Steven Pinker, 71, a Canadian psychologist and psycholinguist at Harvard University.

“As a cognitive scientist, I have spent my life thinking about how people think,” Pinker adds. “So the ultimate subject of my fascination would have to be how people think about what other people think, and how they think about what other people think they think, and how they think about what other people think they think they think. As dizzying as this cogitation may seem, we engage in it every day, at least tacitly, and this state of awareness is what is called common knowledge.”

Pinker’s new book, When Everyone Knows That Everyone Knows, examines the social ramifications of this kind of coalescing, and seeks to untangle how this cognitive ability has impacted history, culture, society.

What do they look like, the mental acrobatics that govern our social world? Excerpts from an interview.

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Common knowledge is not just “what everyone knows” but “what everyone knows that everyone knows”. That sense of acknowledgement of an idea is crucial, isn’t it?

I open the book with the story of the emperor’s new clothes, which I think captures this distinction; because when the little boy points out that the emperor is naked, he isn’t telling them anything they don’t already know.

Yet, as soon as he said it, now everyone knew that everyone else knew, and this became common knowledge. They went from privately knowing, to everyone knowing, to everyone knowing that everyone knew.

And the point of the story, of course, is that common knowledge can change everyone’s relationship with a person or a situation.

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Even children intuitively tap into this. How does that happen?

A problem I faced when writing the book, which scholars of common knowledge also face, is a paradox. We have finite brains and can’t fit an infinite number of “I know that she knows” thoughts into them. We cannot possibly actively keep track of the things we know that others know and know we know. At the same time, the knowing is in play.

We are observing each other, conducting ourselves, checking off thousands of boxes in the course of a single day’s interactions. So how do we do it?

The answer is that common knowledge can be granted at a stroke by an event that is self-evident or public or out there; like the little boy blurting out that the emperor was naked. In just one moment, we get common knowledge and don’t have to think through all those layers of “I know that she knows that I know”.

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You’ve written on rationality, optimism, language. How did this theme come about?

The common thread through all my books is human nature. As a cognitive psychologist, I’m interested in what makes us tick, how we think. I’m interested in how individual minds coordinate, because we’re social animals. Language allows us to do that. This book originated from my interest in language, because it generates common knowledge.

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How has the social-media age affected the idea, and applications, of common knowledge?

Social-media knowledge is a little paradoxical because there’s a sense in which it is not common knowledge. After all, it’s delivered as a personalised feed determined by an algorithm. On the other hand, in social media, with the like, repost, and retweet buttons, you know that anything can go viral. In this sense, it can generate common knowledge.

It is said that the world is becoming increasingly polarized because of our online world. But weren’t communities always in separate bubbles?

Before the mass media, the world was even more fragmented. What we’re seeing now is a kind of re-fragmentation, taking us back to the villages, tribes and clans that characterised humans before there were mass media.

When the media are fragmented, it can also mean that our sense of a moral community comprised of the entire nation or even the entire planet is harder to retain. This is evident in the rise of populism and nationalism in my country and yours, India and the US.

Common knowledge by definition refers to some inherent group of knowers. How big that group is depends on the medium of disseminating information. It could be just two people in conversation.

Social media could lead to more fragmentation because the answer I get is not the answer the next person gets; it’s no longer like Wikipedia, where everyone opens the page and sees the same thing. That’s why there will still be a major role for the BBC, The New York Times, Hindustan Times and other sources dedicated to fact.

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Should it be called common acknowledgement, rather than common knowledge — given that so much of it is subjective?

In cases where the information is not objectively true, it is more accurate to call it common belief (“I believe with 90% confidence that she believes with 90% confidence that I believe with 90% confidence…” and so on). But common belief with sufficiently high probability works like common knowledge.

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As humans we sometimes go out of our way to avoid creating common knowledge too. Where does that fit in?

A fact about language that’s been well known to linguists for a long time is that we very often don’t mean what we say. If you were to apply an algorithm to the meanings of the words and the syntactic rules we use to combine them, you would not actually get out what the speaker intended, which is why it took so long to get computers to understand ordinary human conversation.

Take a sexual come-on, for example. “Would you like to come upstairs and see my etchings?” Any grown woman knows what that means.

In public demonstrations, I tell the joke from the Soviet era about a man handing out leaflets in Red Square. Of course, the KGB arrest him and take him to headquarters, only to discover that the leaflets are blank. They confront him: What is the meaning of this? He says, “What is there to say? It’s so obvious.” That’s a joke about common knowledge.