How Common Knowledge Shapes the World, with Steven Pinker

Overview

Steven Pinker (discussed with Neil deGrasse Tyson and others) argues that common knowledge—where people not only know something, but also know that others know it, indefinitely—underpins how humans coordinate, sustain social institutions, and maintain relationships. He frames the concept as a psychological phenomenon with major consequences for money, power, language, norms, humor, markets, and politics.

Core Ideas About Common Knowledge

• Common knowledge enables coordination: It’s essential for people to “be on the same page,” cooperate reliably, and take actions that others can be expected to match.
• Institutions and “social reality” depend on it:
  • Money works only because everyone treats currency as valuable due to shared expectations.
  • Authority (e.g., presidents, governors, corporate roles, religious roles) functions because people collectively treat those positions as real.
• Language and conventions are built from it:
  • Even words like “rose” refer to specific things because everyone shares the mapping and knows others do too.
  • Everyday conventions (like which day people stay home) operate similarly.

How Common Knowledge Gets Generated

Pinker emphasizes that humans don’t consciously track the infinite layers of mutual awareness. Instead, they treat events as public/salient—what’s “in your face”—so shared perception effectively “packages” the mutual knowledge.

Non-verbal signals as efficient generators

Especially in the case of:

• Laughing, blushing, crying: People know they’re experiencing it and can infer that others see it too.
• Eye contact: A major “common-knowledge generator,” since it signals simultaneous mutual attention and can shift relationships (e.g., seduction, threat, or solidarity).
• Facial expressions and bodily cues: Discussed as evolutionary remnants; Darwin is invoked to argue that many emotion expressions are shared across humans.

Relationships, Face-Saving, and “Acceptable Duplicity”

Social relationships depend on implicit mutual awareness—e.g., understanding what it means to be friends requires knowing that you both know.

Because making intentions fully explicit can destabilize relationships, Pinker discusses ways people avoid complete publicity, including:

• Euphemism / innuendo to keep certain knowledge from becoming fully public.
• “Weasel words” and benign hypocrisy/duplicity, where both parties tacitly understand something without forcing it into an explicit transactional frame.
• A key distinction: some communication allows possible deniability, helping preserve face (social standing). He contrasts this with situations that become “crass” when direct payment or direct sexual intent strips away the plausible social frame.

Common Knowledge in Culture Clashes and Politics

Misunderstandings arise when people assume shared norms that aren’t shared across cultures, producing culture shock and sometimes severe consequences (including war).

Pinker argues cultures differ in:

• the mixing of relationship models (communal sharing, hierarchy, transactional exchange),
• resources (money, favors, sex),
• contexts (home, school, public),

which changes what is considered legitimate or “known.”

Virality: Markets, Rumors, and Shortages

Common knowledge can become “virulent”: public uncertainty can trigger self-fulfilling cascades.

Examples include:

• Bank runs: A rumor that others are worried makes people worry more, causing withdrawals that can collapse a bank even if it wasn’t truly in trouble.
• Toilet paper hoarding: Shortages can emerge less from supply problems and more from shared belief that others will hoard. Pinker notes that store limits may reduce panic only if people interpret them as evidence others can’t strip shelves.
• Speculative bubbles: Treated as common-knowledge games (the “greater fool” logic), where buying rises because participants expect others to buy later.
• Political momentum and elections: Compared to a “Keynesian beauty contest,” where voters choose based on who seems likely to win—not only on candidate quality.

Norm-Breaking, Polarization, and Fractured Common Knowledge

Pinker claims polarization grows when shared norms lose credibility, especially norms maintained because people believed others would enforce them.

He argues society splits into separate “pools of common knowledge,” driven by:

• media ecosystems (cable news and social media),
• residential/class segregation,
• weakened cross-societal organizations that previously mixed people.

As common knowledge fragments, it becomes easier to treat opponents as enemies and intensify vituperation (mean, nasty, contempt-driven discourse).

Recommended Remedy for Better Discourse

Pinker suggests promoting norms such as:

• civil disagreement
• epistemic humility
• charity

He criticizes the “war” metaphor in arguments and proposes truth-seeking should resemble scientific processes: exchanging information and converging through an iterative “random walk.”

The goal is less vituperation and more truth, with science as a model.

Presenters or Contributors

• Steven Pinker
• Neil deGrasse Tyson
• Chuck (StarTalk co-host/contributor)
• Gary (StarTalk co-host/contributor)