Podcast Summary: People I (Mostly) Admire

Episode 167 – The Secret of Humanity? It’s Common Knowledge
Date: September 27, 2025
Host: Steve Levitt
Guest: Steven Pinker

Overview

In this episode, Steve Levitt is joined by Harvard linguist and cognitive psychologist Steven Pinker to explore the surprisingly profound impact of "common knowledge" on human society. They trace how this concept underpins coordination, cooperation, social norms, and even the controversial realm of cancel culture. Drawing on Pinker’s new book, When Everyone Knows That Everyone Knows, the conversation weaves together economics, psychology, language, and evolutionary biology to reveal why common knowledge may be one of humanity’s most essential—and underappreciated—foundations.

Key Discussion Points & Insights

1. The Shifting Value of Rationality and Science

• Rationality and public skepticism: Pinker reflects on changing attitudes toward rationality and science, noting their increasing politicization and the false dichotomy between rationality and emotion.

  “Does reason mean that you’ve got to be a grim, emotionless drone...? I had to disabuse people of the idea that using reason means that there’s no such thing as human goals, preferences, emotions, so on.” – Steven Pinker (02:31)

• Rationality in economics: Levitt and Pinker agree that strict rationality is an academic modeling convenience, not a reflection of actual human behavior, and discuss behavioral economics as a necessary corrective.

  “The game was: give me any behavior I see in the world and let clever people try to reconcile that with rational behavior… And I found it really off-putting.” – Steve Levitt (04:31)

2. What Is Common Knowledge?

• Definition and importance: Common knowledge is when not only does everyone know something, but everyone knows that everyone knows, and so on, recursively.

  “Common knowledge ratifies our social relationships… These relationships depend on common knowledge. By avoiding [it] with an innuendo, you don’t blow up the relationship, but you still convey the message.” – Steven Pinker (06:56)

• Language and social roles: Politeness, innuendos, veiled threats, and “reading between the lines” exist to avoid creating common knowledge that could upend relationships.

Main Point:

“If we as a species didn’t have the ability to do the mental processes involved in understanding common knowledge, the entire nature of collective life and human relationships would be impossible.” – Steve Levitt (11:41)
“No, that is exactly right.” – Steven Pinker (12:11)

Applications:

• Currency value, bank runs, speculative bubbles—all can be traced to shared beliefs and expectations, i.e., “Keynesian beauty contests.”
• Ceremonies, law, and ritual serve to publicly generate common knowledge for coordination.

3. Common Knowledge, Social Coordination, and Game Theory

• Coordination problems: Referencing Thomas Schelling’s parables, Pinker illustrates how coordination requires common knowledge or, at minimum, salient focal points.

  “In the absence of common knowledge, the next best thing is common salience, what he [Schelling] calls a focal point.” – Steven Pinker (15:10)

• Game theory: Levitt explains that economists assume common knowledge in models for mathematical tractability, not realism, but Pinker argues that it mirrors social reality:

  “Social life is game theory. We do coordinate; we do try to outsmart each other.” – Steven Pinker (21:21)

• Examples:

  • Bank runs/toilet paper hoarding: Socially amplified beliefs lead to self-fulfilling outcomes.

    “It wasn’t necessarily that the manufacturers couldn’t keep up with the demand… but worrying that other people might think there’s a shortage.” – Steven Pinker (21:21)

  • Super Bowl ads: Used to launch products with network effects because they generate widespread, simultaneous common knowledge.

4. Common Knowledge in Nature and Evolution

• Nonhuman analogs: Corals synchronize spawning with the moon, a “public” cue, showing that coordination doesn’t always require recursive mentalizing.
• Theory of mind: Human ability to reason about the minds of others (and their beliefs about us) expands the possibilities of coordination beyond fixed signals.

  “Coordination doesn’t literally require the intermediate step of knowing what other people know. We humans do it—and that’s why we can coordinate in hundreds of ways. In the coral, it’s just hardwired.” – Steven Pinker (28:26)

5. Body Language as Common Knowledge Generators

• Eye contact: A public “signal” establishing mutual recognition and often used in dominance, mating, or conflict.

  “You’re looking at the part of the person that’s looking at the part of you that’s looking at the part of them looking at the part of you…” – Steven Pinker (30:12)

• Blushing, laughing, crying: Involuntary, public signals that create common knowledge of emotional states and norm breaches, often fostering trust or apology.

  “Blushing is endearing… it makes an implicit apology credible… Because you can’t make yourself blush. If you’re blushing, then deep down you really mean it.” – Steven Pinker (34:46)

Cancel Culture, Social Norms, and Academic Freedom

6. The Dynamics of Cancel Culture

• Public norm enforcement: Punishment for perceived transgressions is tied to violations made public, which threaten the existence of shared norms.

  “If a norm appears to be flouted in a public forum, everyone has the sense that threatens the norm, and they feel the urge to prop up the norm by punishing the norm breaker in public...” – Steven Pinker (40:41)

• Private vs Public: Attitudes differ dramatically depending on whether statements are made privately or become “common knowledge.”

  “Some of the opinions that can get you canceled… I suspect a lot of people believe, including the people doing the canceling.” – Steven Pinker (42:52)

7. The Weaponization of Belief

• Identity over truth: Large issues (like crime, climate, race) are often not about truth-seeking but are “badges” of tribal loyalty.

  “Your beliefs are signs of your moral commitments… Beliefs are often signals of tribal loyalty, not of degrees of credence in the objective state of the world.” – Steven Pinker (45:11)

8. Defending Academic Freedom

• Pinker describes his role in founding the Council on Academic Freedom at Harvard, especially after fellow academics faced public shaming and professional repercussions for expressing scientific views.

  “It wasn’t about me… but what happened to one of my associates… She was driven out over this bogus accusation that she said something transphobic, and that’s what set a number of us over the edge.” – Steven Pinker (49:16)

• Attacks on academic freedom now come from both the left (within) and the right (outside/through government).

  “Most of the attacks from within the university come from the left. Most of the attacks from outside the university come from the right.” – Steven Pinker (51:51)

Progress, Pessimism, and Predictions

9. Is Progress Inevitable?

• Long-term trends: Pinker argues most indications of progress remain positive—declining poverty, mortality, etc.—though recent years have seen setbacks (e.g. war, democracy).

  “I don’t think any aspect of progress is inevitable. It’s the result of human beings seeing problems, trying to solve them… To the extent that we do that, progress can continue; but to the extent that we do stupid things, then it won’t.” – Steven Pinker (53:08)

• Current threats: Levitt and Pinker both worry about rising anti-science attitudes and the erosion of the rule of law in the US.

  “It never really occurred to me in my own lifetime that the US could descend into some sort of nightmare scenario. But now I do see some possibility, although remote.” – Steve Levitt (54:40) “Some of the great ideas of the Enlightenment... all of which the current administration is oblivious to and trying to undo. The idea that government is a system empowered by a rule of law, that’s not an intuitive idea.” – Steven Pinker (55:15)

• Final note of guarded optimism: Pinker sees possibilities for self-correction if the consequences of bad policies become common knowledge and society recalls its democratic roots.

Notable Quotes & Memorable Moments

• On innuendo and relationships:

  “By avoiding common knowledge with an innuendo, you don’t blow up the relationship, but you still convey the message.” – Steven Pinker (06:56)

• On public signals:

  “There are some signals that generate common knowledge. They’re public. You see them when you know that everyone else is seeing them… that can give you common knowledge at a stroke.” – Steven Pinker (12:11)

• On Super Bowl ads:

  “It isn’t just the number of eyeballs, it’s that those eyeballs know that there are other eyeballs.” – Steven Pinker (25:07)

• On blushing:

  “Blushing is endearing… it makes an implicit apology credible… Because you can’t make yourself blush.” – Steven Pinker (34:46)

• On cancel culture driver:

  “If a norm appears to be flouted in a public forum, everyone has the sense that threatens the norm, and they feel the urge…to prop up the norm by punishing the norm breaker in public.” – Steven Pinker (40:41)

Timestamps for Critical Segments

• Introduction to Steven Pinker and context: 01:18
• Rationality, science, and their politicization: 02:31 – 06:04
• Defining and expanding common knowledge: 06:56 – 12:11
• Economic examples & coordination: 09:14 – 15:10
• Game theory and academic assumptions: 19:15 – 21:21
• Super Bowl ads and network effects: 23:43 – 26:31
• Common knowledge in animals; theory of mind: 26:31 – 30:12
• Body language (eye contact, blushing): 30:09 – 34:46
• Cancel culture and social enforcement: 40:25 – 44:25
• Belief as tribal identity: 45:11 – 46:38
• Academic freedom battles and balance of threats: 49:05 – 51:51
• Progress and setbacks: 53:08 – 56:53
• Final reflections on Enlightenment values: 55:15 – 56:53

Tone and Style

Throughout the episode, the discussion is intellectually playful and candid, blending stories, research, and broad philosophical reflections. Pinker’s language is precise yet accessible, with flashes of dry humor. Levitt’s tone is curious, occasionally self-deprecating, and seeks practical connections between abstract theory and the real world.

This engaging dialogue reveals how a simple-sounding concept—common knowledge—shapes everything from the money in your wallet to the latest social controversy, and why our ability to generate and manipulate shared understanding may be the beating heart of human civilization.