StarTalk Radio

What Everyone Knows You Know with Steven Pinker

January 23, 2026

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  • Common knowledge, defined technically as a situation where everyone knows that everyone else knows something *ad infinitum*, is the invisible glue necessary for social coordination, underpinning institutions like money, power, and language. 
  • Conspicuous non-verbal signals like laughter, blushing, and crying function as powerful 'common knowledge generators,' making private emotional states or intentions publicly verifiable. 
  • The fracturing of shared common knowledge, often exacerbated by media silos, contributes to societal polarization by creating separate informational realities within a single culture. 
  • The ideal norms for civil disagreement should prioritize epistemic humility and charity over the natural human tendency to treat argument as a competition or war. 
  • A mathematical proof by Robert Allman suggests that rational agents should not agree to disagree, proposing an alternative model for argument where information exchange leads to convergence on a common conclusion rather than a winner-take-all scenario. 
  • Neil deGrasse Tyson concludes that the human mind is the hardest thing to study in the universe, noting it is the source of civilization but potentially its end if not carefully managed. 

Segments

Introduction of Steven Pinker
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(00:01:27)
  • Key Takeaway: Steven Pinker is introduced as the expert guest for the StarTalk Radio episode, What Everyone Knows You Know with Steven Pinker.
  • Summary: The segment marks the official start of the interview portion of the podcast. Steven Pinker, a cognitive scientist and author, is welcomed by Neil deGrasse Tyson and Chuck Nice. The episode will focus on human psychology and recursive common knowledge.
Defining Common Knowledge
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(00:02:10)
  • Key Takeaway: Common knowledge requires an infinite chain of mutual awareness (I know that you know that I know, etc.) and is essential for human coordination.
  • Summary: Humans rely on social creatureship and language for coordination, but the underlying mechanism is common knowledge. This concept involves knowing something, knowing that others know it, and knowing that they know that you know it, extending infinitely. This shared understanding is crucial for social behavior and coordination.
Book Title and Definition
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(00:05:33)
  • Key Takeaway: Pinker’s book title, When Everyone Knows That Everyone Knows, emphasizes the infinite recursion required for technical common knowledge, which is distinct from private knowledge.
  • Summary: The full title of Pinker’s book is revealed to be When Everyone Knows That Everyone Knows, dot, dot, dot: Common Knowledge and the Mysteries of Money, Power, and Everyday Life. The ‘dot, dot, dot’ signifies the infinite layers of mutual knowledge required for the technical definition.
Coordination and Institutions
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(00:07:40)
  • Key Takeaway: Common knowledge is necessary for coordination, as demonstrated by the value of money and the authority of government, which rely on shared belief in their existence.
  • Summary: The value of currency, like a dollar bill, exists only because everyone knows that everyone else treats it as valuable. Similarly, governmental power is maintained because the citizenry collectively treats leaders as authoritative figures.
Schelling’s Lost Couple Example
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(00:09:15)
  • Key Takeaway: The Schelling example illustrates that coordination requires common knowledge, as simple mutual knowledge is insufficient for two people to reliably meet up in a complex environment.
  • Summary: If a lost couple needs to meet, simply knowing where the other might go is insufficient due to recursive uncertainty. Only common knowledge—knowing that the other person knows where you will be—guarantees they meet at the same location.
Generating Common Knowledge
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(00:10:39)
  • Key Takeaway: Common knowledge is often generated instantly through public, salient events that are impossible to ignore, bypassing the need to consciously track infinite layers of knowledge.
  • Summary: Because tracking infinite layers of knowledge is mentally taxing, common knowledge is often established at a stroke when an event is public or salient. This shared, observable experience implicitly establishes the necessary recursive knowledge.
Euphemism and Veiling Intentions
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(00:11:25)
  • Key Takeaway: People use euphemism and innuendo to prevent things from becoming common knowledge, such as in the metaphor of being ‘in the closet.’
  • Summary: Language is used not only to establish common knowledge but also to conceal it. Euphemisms allow individuals to hint at intentions without making them explicitly public, thereby avoiding changes in social dynamics.
Acceptable Duplicity and Weasel Words
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(00:15:30)
  • Key Takeaway: Acceptable duplicity involves situations where both parties are aware of an underlying truth but use veiled language (like ‘Netflix and chill’) to avoid making it common knowledge and thus preserve a relationship dynamic.
  • Summary: Veiled language, or ‘weasel words,’ allows for transactional interactions (like bribery or seduction) to occur without explicitly establishing a dominance or transactional relationship, thereby saving face. Plausible deniability relies on the lack of common knowledge regarding the true intent.
Cultural Variation in Relationships
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(00:22:17)
  • Key Takeaway: Cultural differences arise from varying norms regarding which resources (e.g., brides, land) are exchanged within different relationship models (communal, hierarchical, transactional) and contexts.
  • Summary: Cultures differ not in the phenomenon of common knowledge itself, but in how they apply it to negotiate relationships. Competent cultural membership involves mastering the specific common knowledge dictating what resources can be exchanged in specific contexts.
Non-Verbal Common Knowledge
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(00:24:27)
  • Key Takeaway: Conspicuous non-verbal displays like laughing, blushing, and crying serve as powerful common knowledge generators, making private emotional states or intentions publicly verifiable.
  • Summary: Darwin noted that facial expressions, like blushing, are universal and serve to make internal states public. Blushing, for example, makes the internal feeling of heat common knowledge because others can see the color change, and you know they can see it.
Eye Contact as a Signal
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(00:30:56)
  • Key Takeaway: Prolonged eye contact is an uncomfortable but potent common knowledge generator, historically signaling either threat or the establishment of a shared, non-private understanding.
  • Summary: Among primates, direct eye contact is a threat signal, a dynamic that persists in humans where prolonged staring can signal aggression or intimacy. Asking someone to look you in the eye is a demand to make a private assertion common knowledge.
The Emperor’s New Clothes
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(00:35:35)
  • Key Takeaway: The story of the Emperor’s New Clothes is a classic example where a child’s statement converts private knowledge (the emperor is naked) into common knowledge, instantly shifting the relationship from deference to scorn.
  • Summary: The child’s utterance did not reveal new information but made the existing private knowledge public. This act of establishing common knowledge immediately changed the social relationship, replacing deference with ridicule.
Virulence of Common Knowledge
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(00:43:02)
  • Key Takeaway: Rumors can become self-fulfilling prophecies, as seen in bank runs or the COVID-19 toilet paper shortage, where the belief in a shortage causes the actual shortage.
  • Summary: In a bank run, the fear that others fear insolvency causes everyone to withdraw funds, leading to failure even if the bank was sound. Similarly, Johnny Carson’s joke about toilet paper shortages created the shortage by triggering hoarding based on shared expectation.
Keynesian Beauty Contest
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(00:47:15)
  • Key Takeaway: Speculative investing, like in crypto, functions as a Keynesian beauty contest where the goal is not to pick the best asset, but to pick the asset others will pick next, reflecting a recursive common knowledge problem.
  • Summary: Keynes compared speculative investing to a beauty contest where participants try to guess what the majority will choose, rather than judging intrinsic value. This dynamic is also seen in primary elections where voters focus on momentum rather than a candidate’s inherent suitability.
Fracturing of Norms
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(00:49:37)
  • Key Takeaway: The flouting of established political norms by figures like Donald Trump erodes those norms if the expected negative consequences do not materialize, leading to further polarization.
  • Summary: When leaders repeatedly violate norms of civility or honesty without consequence, those norms cease to exist as common knowledge expectations. This fracturing of shared understanding contributes to negative polarization, where opposing sides view each other as inherently evil.
Argument as War Metaphor
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(00:54:55)
  • Key Takeaway: The common use of war metaphors in discussing argument hinders truth-seeking, contrasting with mathematical models suggesting rational agents should exchange information to converge on a conclusion rather than simply ‘winning’ a debate.
  • Summary: The prevailing metaphor of argument as combat prevents genuine discovery of truth. Mathematical proofs suggest that rational agents should not ‘agree to disagree’ but rather exchange information until they converge on a common conclusion.
Norms for Civil Disagreement
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(00:54:36)
  • Key Takeaway: Civil disagreement requires norms like epistemic humility and charity, counteracting the natural human tendency to frame arguments as competitive wars.
  • Summary: The desired norms for spreading include civil disagreement and epistemic humility, which run counter to human nature’s inclination to view argument as a competition. Metaphors of war are commonly used when discussing arguments, such as ‘I demolished them.’ A different model for argument, derived from a mathematical theorem, suggests that instead of one side winning, rational agents should converge on a common conclusion through information exchange.
Argument Paradigm Shift
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(00:55:02)
  • Key Takeaway: The optimal method for discovering truth involves a random walk of information exchange leading to convergence, not compromise or one side winning.
  • Summary: Robert Allman’s proof, dependent on common knowledge, sets an alternative paradigm for argument. Truth is not found by compromise, as the truth is unlikely to lie halfway between two opinionated individuals. Instead, information exchange facilitates a random walk until the participants converge on a shared conclusion, a process scientists use when designing experiments to resolve disagreements.
Cosmic Perspective on the Mind
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(00:56:56)
  • Key Takeaway: The human mind represents the most complex challenge in the universe, potentially being both the source of civilization and its ultimate downfall.
  • Summary: Neil deGrasse Tyson reflects that while the universe is vast and governed by known laws of physics and chemistry, the human mind is the hardest thing to contemplate. Psychologists and neuroscientists are engaged in the difficult task of understanding ourselves. If the study of the human mind remains the most complex endeavor, its illogical and occasionally irrational nature could lead to the end of civilization if caution is not exercised.