Summary

Pinker explores common knowledge – the distinction between everyone knowing something versus everyone knowing that everyone knows it. This seemingly subtle difference drives coordination games, social relationships, and collective behavior. Language cheaply generates common knowledge that makes social coordination possible, while indirect speech and plausible deniability let us navigate situations where full transparency would be socially costly.

The book examines how recursive mentalizing ("I know that you know that I know") develops around age 8-10, with adults typically handling about 4 levels. Social phenomena like face, status hierarchies, and emotional expressions all function as common knowledge generators. Pinker connects this to cancel culture as the urge to prevent ideas from becoming common knowledge, and explains why we often don't say what we mean – the art lies in selecting the optimal level of vagueness.

Quotes

Language cheaply generates the common knowledge that makes social coordination possible.

Legal systems are not just coercive, they're expressive.

Eye contact is the ultimate common knowledge generator.

Key Takeaways

Notes

1: Common knowledge + why it matters

• Common knowledge: statement widely known to be true
• Two features that make it key to understanding human life:
  • Instantly imparted by a conspicuous event
  • Can unite people in action, disrupt the social status quo
• Learnings of book:
  1. “Learning about something in public, even if everyone already knows it, can change everything”
  2. “The main thing that common knowledge changes is the ability to coordinate”
  3. We’re particularly aware of it since it’s so potent
  4. This has empowered us to leverage in communities, economies, nations
  5. Personal relationships are also common knowledge games
• Common vs mutual knowledge
• Eg. language is common knowledge
• Fairness (eg. prisoners dilemma) vs coordination
• Conventions: solution to coordination
• ↑ creates “non-physical realities”, not “shared fictions” (Harari)
• Super Bowl ads uniquely generate common knowledge
  • Great for network externalities, companies reliant on brand image
• Crypto speculation
• Pluralistic ignorance:lack of common knowledge necessary for action
• Cancel culture: intention vs perception
• With social media / digital town squares, millions of people can now generate common knowledge
• Punitive mobbing
• Social relationships are ratified by common knowledge
• Idioms for common knowledge:
  • The cat is out of the bag
  • It’s on the record
  • Spilled the beans
  • The closet
  • The bell can’t be un-rung
• Idioms for avoiding common knowledge:
  • The emperor has no clothes
  • Look the other way
  • Buried their head in the sand
  • Elephant in the room

2: Common knowledge + common sense

• Necessarily infinite (eg. general couriers)
• Common knowledge is never really 100%, more like “common 0.9 belief”
• Hub+spoke → distributed computing with handshake protocols
• Rational agents cannot agree to disagree
• Bayes’ rule + ↑: posteriors cannot be different with common knowledge, only shared knowledge
• Rational argument should be a random walk (updating priors)
• Rational markets: assumes common knowledge and priced in
• Rational debate tips:
  • State confidence in probabilities
  • Steel man the other case
  • Agree to adversarial collabs
  • Bet on concrete predictions

3: Coordination games

• Nash equilibrium
  • Thus, altruism > rationality
  • “Calls for a higher rationality in which actors submit to a social contract that ties their hands for their own good”
• Self-signaling, self-committing
• “Language cheaply generates the common knowledge that makes social coordination possible”
• The battle Of the sexes: hypothetical scenario with 2 equilibrium, where each actor prefers the other
  • Need fair coordination
• Hunting stag together or hare alone
• The chicken game: worst if both defect
• The hawk / dove game:
  • War when both mistakenly think they’re the hawk
• The madman strategy: win or catastrophe play in hawk/dove game
• “Legal systems are not just coercive, they’re expressive”
  • Ie. norms > law enforcement
  • Eg. no smoking in public spaces

4: How we get inside each other’s heads

• 1. recursive, 2) reflexive, 3) ↓
• Self-evident → common knowledge
• Theory of mind develops around 3-4yo
• The curse of knowledge: learned knowledge from one is assumed upon other people → jargon
• Recursive mentalizing around 8-10yo
  • The age of reason: ↑
• Generally, adults have 4 slots for recursive mentalizing
  • Eg. “Of course I care about how you perceive I wanted you to feel”
  • Eg. “I know you think you understand what you thought I said, but I’m not sure you realize what you heard is not what I meant”
• Humans have content-addressable memory vs computers with arbitrary address storage
  • Eg. only 1 slot for “X believes”
• Solution: chunking of related concepts
  • Alt. macros, caching, memorization
• ↑ mental scripts with pre-packed beliefs about beliefs
  • Eg. bluff, doubt, humor, persuade, suspect, scandal, argument
• Study: pick a number between 1-100, then take 2/3ds, what’s average?
  • Recursive mentalizing solution: 0
  • Most people 20-35
  • Though, actual answer (non-rational) is 20s
• ↑ bubbles can be rational: average expectation of the average
• Bank run: “the only thing we have to fear is fear itself”
• Keynesian beauty contest
• The volunteer dilemma: bystander effect game theory - volunteer incurs cost, others benefit
• ↑ responsibility defuses with common knowledge

5: Social relationships as coordination games played with reputation, symbols, and face

• Scrutiny of conspicuous charity
• Reputation for charitability
• Common knowledge charity doesn’t allow evaluation of true altruistic nature
• Signals of relationships:
  • Exchange
  • Status
  • Communal warmth
• Social paradoxes:
  • We try to gain status by not caring about status
  • We rebel against conformity in the same way as everyone else
  • We show humility to prove we’re better than other people
  • We don’t care what others think, and we want them to think this
  • We make anonymous donations to not care about getting credit
  • We bravely defy social norms so that people will praise us
• ↑ back and forth between social judgement and recursive mentalizing
• ↑ don’t want it to be common knowledge, just mutual
• 4 evolved relational models:
  1. Communal sharing
     • Language focal points
  2. Authority ranking
     • Authority markers
  3. Equality matching (equity, fairness)
  4. Market pricing / rational legal
• Face: common knowledge of the deference + sympathy they expect to be granted
  • Eg. “To spend more time with family” is a verbal courtesy
• Study: presence of an audience 2x’s likelihood of escalation to violence
• In more orderly societies, social hierarchies are ordered by status, not dominance
  • Implicit promise of “I could help you”
• ↑ leadership: initiative, intelligence, competence, generosity
• Battle of the sexes:
• ↑ many forms of entrenched inequality are arbitrary
• Ambiguity between relational models can create tension
• Communities (eg. orgs, countries) also utilize 4 relational models

6: Conspicuous emotional expressions as common knowledge generators

• Comedy / laughter generates common knowledge that….
  • Challenges a convention of dominance, status, or prestige
  • Shift relational model from dominance to communality
• Laugher is social (only around others), contagious, involuntary
  • “Against the assault of laughter, nothing can stand”
  • Contagion ensures safety in numbers
• Crying is surrender, neediness
• Other emotions*
• Blushing - conspicuous shame, earns forgiveness and trust
• “Eye contact is the ultimate common knowledge generator”

7: Why we don’t just come out and say what we mean

• Off-record, indirect speech: innuendo, euphemism, subtext
  • Plausible deniability
• Hyperbolic acknowledgments:
  • Eg. “could you please pass the salt?”
• The driver’s dilemma: game theory where indirectness helps Sus out conspirator status (eg. bribe)
• The art is selecting the optimal level of vagueness
• “Plausible deniability of common knowledge of the intent”
• Direct propositions are broadly interpretable, lossless (bystanders)
• Even applies to self (eg. viewing self as moral)

8: The cancelling instinct

• The urge to prevent ideas from becoming common knowledge
• Intellectual repression, eg. for protected speech / peoples
• Threats to freedom of speech:
  • People hold beliefs as facts not due to truth, but upholding moral order
  • Upholding a moral order takes place in the arena of common knowledge
• Can’t repress disagreement
• Educational institutions rightfully need to restrict speech sometimes*
• Censorship by publishers to prevent common knowledge
  • Eg. race differences
• Affirmative action is an example of pluralistic ignorance (majority against)
• Alt policy to limiting intellectual expression: “don’t go there”
  • Where even exploring it leads to harm
  • Eg. socially damaging info
  • Justified by reasoned argument
  • Benefits of limited agnosticism vs cost of ignorance

9: Why not everything should be common knowledge

• Historic trend is transparency and openness
• Radical honesty + transparency:
  • Embraced in Silicon Valley, Bridgewater Associates
• Everyone has scandalous, illegal thoughts → reciprocal knowledge, but can’t be common knowledge
• “Politics is the art of keeping tradeoffs out of common knowledge”
• Common knowledge = higher-order rationality