StarTalk Radio: “What Everyone Knows You Know” with Steven Pinker

Host: Neil deGrasse Tyson
Guests: Steven Pinker, Chuck Nice, Gary
Date: January 23, 2026

Episode Overview

In this Special Edition of StarTalk Radio, Neil deGrasse Tyson welcomes renowned cognitive psychologist Steven Pinker to discuss the concept of common knowledge—what it is, how it shapes human society, and its impact on everything from economics and politics to comedy, relationships, and cultural norms. Drawing from Pinker’s latest book, “When Everyone Knows that Everyone Knows: Common Knowledge and the Mysteries of Money, Power And Everyday Life,” the conversation dives into the power of shared understanding, coordination, social signaling, and the profound role these mechanisms play in maintaining (or dissolving) the fabric of civilization.

Key Discussion Points & Insights

1. Defining Common Knowledge

• What is Common Knowledge?
  • Pinker distinguishes between private knowledge (“everyone knows something”) and common knowledge (“everyone knows that everyone knows, and so on, ad infinitum”) [06:00].
  • Quote (Pinker, 05:54):

    “Common knowledge, in the technical sense, refers to the situation where I know something. You know it. I know that you know it, you know that I know it… ad infinitum. So it's when everyone knows that everyone knows.”

2. Common Knowledge and Social Coordination

• Why It Matters:
  • Coordination: It enables humans to align actions, expectations, and social roles—“civilization depends on common knowledge” [07:40]. Institutions (government, money, corporations) exist because people share a mutual recognition of their roles and value [08:13].
  • Example: The value of money arises only because “everyone knows it is valuable, and everyone knows that everyone knows it is valuable” [07:38].
• Thomas Schelling’s Example: A couple lost in pre-cell phone Manhattan must rely on shared conventions to find each other, illustrating the need for common knowledge to coordinate (e.g., both guessing a “public” meeting place) [09:00].

3. Human Signaling, Euphemism, and Acceptable Duplicity

• Weasel Words and Plausible Deniability:
  • Social interactions often avoid full explicitness, maintaining plausible deniability—think of euphemisms (“Netflix and chill”), veiled bribes, and innuendo to protect relationships and “save face” [15:37, 16:22].
  • Quote (Pinker, 17:18):

    “It's a plausible deniability of common knowledge. Because when you think about it, it's really not that plausible.”

4. Nonverbal Communication as Common Knowledge Generator

• Laughter, Blushing, Crying, Eye Contact:
  • These conspicuous non-verbal displays make private experience public, generating shared understanding about someone’s feelings or intentions.
  • Eye Contact: Among primates (including humans), it can signal threat, seduction, or the creation of mutual awareness (the “infinite loop” of “I know you know I know,” etc.) [28:29, 30:24].
  • Quote (Pinker, 25:04):

    “I suggest that they [laughter, crying, blushing] are common knowledge generators. So when you're laughing, you know you're laughing… Other people know you're laughing… and so on. Blushing… You feel the blood, others see the color change… They know that you know you're feeling it.”

5. Common Knowledge and Cultural Variation

• Cultural Context: What’s commonly known—and how certain resources (money, favors, sex) or relationships are treated—varies widely across cultures [22:21, 23:23].
  • Pinker explains three relationship models: communal, hierarchy/dominance, transactional [22:21].
  • Culture shock happens when you don’t know a new culture’s common knowledge [23:36].

6. Comedy, Education, and Solidarity

• Jokes and Pedagogy:
  • Comedy (and education) depends on shared common knowledge; a punchline only lands if the audience “gets it” [40:11].
  • Humor signals solidarity and “bonds people” because recognizing a joke identifies mutual understanding [41:37].
  • Quote (Pinker, 41:37):

    “If you get the joke, then what has just been made public is something that you privately knew all along. …That’s why humor is such an important bonding agent.”

7. Contagious Phenomena: Bank Runs and Toilet Paper Panics

• Virulence of Common Knowledge:
  • Public rumors (even jokes) can trigger mass behavioral cascades—e.g., bank runs, toilet paper shortages [44:02, 47:16].
    • Johnny Carson’s Joke: A Tonight Show quip about a “toilet paper shortage” created an actual shortage via public panic [47:16].
    • “The only thing we have to fear is fear itself” (Roosevelt) as a practical application of common knowledge theory [44:02].

8. Politics, Social Norms, and Fractured Common Knowledge

• Norm Shattering:
  • Norms exist only so long as people believe they do. Trump (and others) flouting expectations undermined decades-old conventions by publicly violating norms and facing few consequences—copycats then follow [50:31].
  • The fracturing of common knowledge, through media bubbles, leads to increased polarization and the erosion of shared facts [51:05].
• Quote (Pinker, 53:28):

  “There was a norm in politics… that you pretend that you like them even if you don't. And those are some of the norms that are shattered. You don't lie blatantly. … You at least try to pretend that you're honest.”

9. Danger of Distorted (or Weaponized) Common Knowledge

• Polarization: “Negative polarization” means not only disagreement, but mutual vilification. Social networks, cable news, and social sorting have created separate pools of common knowledge, increasing divisiveness and fueling conflict [51:05].
• Advice for Repair: Norms of civil disagreement, epistemic humility, and charitable interpretations in arguments could help restore healthy dialogue [55:18].
  • Mathematical Note: Pinker references Robert Aumann’s theorem that rational agents should not “agree to disagree,” advocating for dialogue aimed at convergence, not combat [56:04].

Notable Quotes & Memorable Moments

On Common Knowledge and Civilization:

• “Civilization does depend on common knowledge, on institutions like government, like money. The only reason… a piece of paper… is valuable is because other people treat it as valuable.” — Pinker [07:40]

On Euphemism:

• “You're completely manipulating the buyer.” — Chuck Nice jokes about Pinker's provocative book title [05:48]

On Blushing and Universality:

• “[Darwin] used similarity in facial expressions… as an argument against… scientific racism of his day… we all descended… from a common ancestor.” — Pinker [26:02]

On Comedy and Bonding:

• “If you get the joke, then what has just been made public is something that you privately knew all along.” — Pinker [41:37]

On Bank Runs and Virality:

• “When Roosevelt said, ‘the only thing we have to fear is fear itself,’ this was a theorem of common knowledge.” — Pinker [44:05]

On Culturally Fractured Knowledge:

• “There has been a segregation into two separate pools of common knowledge… Each one then hung out with people like them. And then the common knowledge that they shared started to grow disjoint.” — Pinker [52:25]

Cosmic Perspective:

• “You know what the hardest thing is? The human mind. …I just hope that the study of the human mind by the human mind is not the most complex thing we ever have to tackle in this universe.” — Neil deGrasse Tyson [57:53]

Important Timestamps

• 01:56 — Introduction to topic: Why is “common knowledge” interesting?
• 05:19 — Pinker introduces his new book and defines common knowledge.
• 07:40 — Common knowledge as the foundation of civilization.
• 09:00 — Schelling’s “meeting in Manhattan” example.
• 15:28 — “Acceptable duplicity” and plausible deniability in social interactions.
• 25:04 — Laughter, blushing, crying, eye contact as generators of common knowledge.
• 28:29 — Eye contact, social norms, and threat signals across primates.
• 41:37 — Comedy and the bonding power of shared knowledge.
• 44:02 — Virulence and bank runs: When rumors go viral.
• 47:16 — Johnny Carson, toilet paper shortages, and the power of public jokes.
• 50:31 — Trump, norm-breaking, and the fragility of social expectations.
• 51:05 — The fracturing of national common knowledge and the rise of polarization.
• 55:18 — Hope for civil disagreement: mathematical models and epistemic humility.
• 57:53 — Neil’s cosmic perspective on the complexity of the human mind.

Tone and Style

The episode is lively, humorous, and intellectually accessible, marked by the playful banter between Tyson, Nice, and Pinker. Listeners are treated both to insightful science and relatable, sometimes irreverent, pop culture references—everything from “Coming to America” and “Friends” to national political events and viral behavioral panics.

Summary Takeaways

• Common knowledge—not just what is known, but what is publicly known to be known—is fundamental to society’s functioning.
• It shapes money, power, relationships, language, and humor, and underlines everything from institutional power to viral fads.
• The move from private to public knowledge can upend hierarchies, spark mass behaviors, or mend/break social bonds.
• Comedy, education, and even basic conversation are all built on shared common knowledge.
• The fracturing of common knowledge threatens social cohesion, but attending to civil discourse and humility in argument offers hope.

Final Quote (Pinker, 57:07):

“That would be the kind of norm, it goes against human nature... But for that norm to spread in journalism, in politics, in the court system would be a good thing. It would be transformative. Yes. More truth, less vituperation.”

Steven Pinker’s latest book:
When Everyone Knows that Everyone Knows: Common Knowledge and the Mysteries of Money, Power, And Everyday Life