The Psychology of Knowing: Professor Steven Pinker on Common Knowledge and the Power of Shared Awareness

On Nov. 12, Harvard Kennedy School’s John F. Kennedy Jr. Forum hosted a conversation featuring Professors Steven Pinker and Jennifer Lerner. The event centered on Pinker’s latest book, “When Everyone Knows That Everyone Knows: Common Knowledge and the Mysteries of Money, Power, and Everyday Life,” which explores how shared awareness—mutual understanding of what others know—shapes cooperation, politics, and social behavior. Drawing from psychology, Pinker examined how this often-overlooked concept underpins everything from government legitimacy and social norms to academic freedom in an age of competing truths.

Lerner opened the discussion by questioning the meaning of “common knowledge:” “In the book, common knowledge has a very specific definition. It’s not something that everybody already knows. It has a more precise definition… Can you tell us what’s special about common knowledge?”

For Pinker, common knowledge describes what allows people to coordinate their actions and understand one another’s intentions. “Common knowledge, in its technical sense, 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, and so on ad infinitum,” he said. 

“It can be generated when we have a sense that something is public, or conspicuous, or out there, or self-evident. When one of us sees something and another one sees it, and each sees the other one seeing it, that generates all of these levels implicitly.”

In academic literature, the concept of common knowledge has long been discussed in fields such as game theory, economics, and philosophy. Philosopher David Lewis first formalized the idea in the 1960s to explain how shared awareness enables cooperation. Since Lewis, mathematician Robert Aumann expanded the concept in 1976 through his “Agreement Theorem,” and later scholars applied it to fields ranging from political science to computer science models of distributed systems. Pinker’s contribution lies in bringing this abstract concept into the realm of psychology and everyday human behavior. 

“It is necessary for coordination—for being two people on the same page,” he stated. “It can be the basis of power, from the dominance and deference relations in everyday life. One person defers to another because he knows that the other one will stand his ground, and the second one will stand his ground because he knows that the first one will defer.”

He added that this logic applies to larger institutions as well. “The power of a government hinges on common knowledge that they have power. Of course, [the] government has the guns, but not enough guns to intimidate every last member of the population.”

“I quote a line from the movie ‘Gandhi’ in which the titular character says to a British colonial officer, ‘In the end, you will leave, because there is simply no way that 150,000 Englishmen can control 350 million Indians if the Indians refuse to cooperate,’” he continued.

Pinker explained that regimes maintain authority by suppressing information. “The regime holds its power because it prevents common knowledge from being generated. [It] suppresses freedom of the press, freedom of speech, freedom of assembly, so that people can’t share the news that their disgruntlement is widely shared,” he said. 

Drawing from his earlier work on rationality, he noted that humans are prone to errors yet capable of great collective achievements. “Despite all of the flaws of human judgment and decision-making that Jen and I are both obsessed with…We’ve discovered DNA. We’ve gotten to the moon. We’ve reduced the toll from scourges like infectious diseases, war, and crime. If we’re so cognitively flawed, how did we accomplish these things?”

Pinker attributes this to the power of institutions that guide human reasoning toward truth and progress. “Part of the answer is institutions,” he explained. “We figure out hacks and workarounds where the flaws of some people can be used to expose the flaws of other people.” 

“That’s why free speech, freedom of the press, [and] open debate are cardinal virtues in a democracy, as they ought to be in academia and in science. Someone proposes an idea; everyone gets to then say what’s wrong with it. You expose it to potential falsification.”

The connection between human imperfection and institutional design that Pinker alluded to has long preoccupied political thinkers. In the “Federalist Papers No. 51,” James Madison famously wrote, “If men were angels, no government would be necessary.” Like Madison, Pinker views democratic systems as protections against the limits of human reason: structures built to channel disagreement rather than suppress it. Yet as modern society confronts newfound pressures on free speech, the same mechanisms meant to correct human error can turn into tools of exclusion. 

This tension between open inquiry and social policing set up the next part of the conversation. 

Pinker then turned to what he calls the “canceling instinct” and described it as a deeply rooted psychological tendency to suppress ideas that threaten widely accepted norms. “I did want to take up the psychological question of why people feel the need to cancel in the first place,” he said. 

“Why is it contrary to what ought to be the ethos of academia—namely, only by expressing an idea can we find out whether it’s any good? Why is there an urge that certain ideas not be expressed at all, leading to the various incidents of cancellations, censorship, punishment, mobbing, and shaming?”

He traced the answer back to common awareness and the role it plays in sustaining moral and social norms. “Our moral and social norms are held up by common knowledge—that something is a norm because everyone knows it’s a norm,” he explained. “Why don’t we tell ethnic jokes the way people did when I was a child, or jokes at the expense of gay people, or jokes about ditzy blondes, or all kinds of things that are almost unthinkable today?”

Pinker noted that because norms exist through common knowledge, they can unravel if they are publicly violated without consequence. “If we follow a norm, we also tend to be norm-policemen,” he said. “We tend to be attentive to people broaching the norm, particularly in a public forum. And if they do, there is a need to prop up the norm by making it common knowledge that you can’t get away with breaching it.”

While this tendency helps uphold civility and respect, Pinker warned that in academia it can be destructive, as people often equate opinions with moral worth. “They’re signs of tribal loyalty, of moral purity,” he said. “These features are poisonous to the collective search for the truth, which is why we allow free speech even when it can be shocking or offensive.”

Pinker’s warning carries particular weight at Harvard, where debates over free expression and inclusion have intensified in recent years. In April 2023, more than 70 Harvard faculty members came together to form the Council on Academic Freedom, co-led by Pinker, with the stated goal of “encouraging the adoption and enforcement of policies that protect academic freedom.” 

Nonetheless, ideas once considered offensive can later become accepted truths. “Often empirical hypotheses or even normative beliefs that seem to be assaults on the moral sensibilities of a day can become unexceptionable in subsequent eras,” Pinker said. “The idea that humans descended from apes was, in its time, considered to threaten the moral order. Fortunately, some people were willing to say it—they were denounced, they survived—and now we just don’t think it’s a major moral issue.”

Pinker concluded on a reflective note: “We can’t study everything. Should judgments of social harm enter into what we do or don’t take up? This is different from repressing a particular opinion, but rather about what questions we should raise.”

Nashla Turcios ’28 (nashlaturcios@college.harvard.edu) writes News for the Harvard Independent.