Mindscape 329 | Steven Pinker on Rationality and Common Knowledge
Audio Brief
Show transcript
This episode explores the concept of common knowledge and its profound impact on human rationality, communication, and social coordination.
There are three key takeaways from this discussion. First, social coordination depends not just on what individuals know, but on what they know everyone else knows. Second, persistent disagreement often stems from irrationality, different starting assumptions, or a strategic refusal to make beliefs common knowledge. Third, much of social etiquette and indirect communication is a sophisticated dance to manage risk by avoiding the creation of common knowledge.
Common knowledge is a state where everyone knows a piece of information, everyone knows that everyone knows it, and this awareness continues recursively. This recursive knowledge is the crucial ingredient for solving coordination problems, from simple greetings to large-scale social movements. Without it, synchronized actions are difficult.
The game theory principle known as Aumann's Agreement Theorem states that two perfectly rational agents, starting with the same prior beliefs, cannot agree to disagree if their updated beliefs become common knowledge. Real-world disagreements persist because individuals may not be fully rational, possess different initial assumptions, or intentionally prevent their beliefs from becoming shared knowledge.
People often use indirect speech, such as hints, innuendo, and euphemisms, to avoid making propositions common knowledge. This strategic ambiguity maintains plausible deniability, allowing individuals to retract or deny intentions if a sensitive proposal, like a bribe or a romantic advance, is rejected. This management of common knowledge is vital for navigating complex social interactions.
Understanding common knowledge reveals the subtle mechanisms through which societies manage information flow and structure human interaction.
Episode Overview
- The episode explores the concept of "common knowledge"—the recursive awareness where everyone knows something, and everyone knows that everyone else knows it—and its profound impact on human rationality, communication, and social coordination.
- It delves into Aumann's Agreement Theorem, a game theory principle stating that two perfectly rational agents cannot agree to disagree, prompting a discussion on why real-world disagreements are so common.
- The conversation examines how indirect speech, such as innuendo and euphemisms, is often used to strategically avoid creating common knowledge, thereby maintaining plausible deniability in sensitive social interactions.
- The hosts discuss various "common knowledge generators," including public announcements and non-verbal cues like eye contact and laughter, which humans use to solve coordination problems ranging from simple greetings to large-scale social movements.
Key Concepts
- Common Knowledge: A state of awareness where everyone knows a piece of information, everyone knows that everyone knows it, and this continues ad infinitum. It is the crucial ingredient for solving coordination problems.
- Aumann's Agreement Theorem: A theorem in game theory which states that if two people are rational Bayesians with the same prior beliefs, and their updated beliefs (posteriors) become common knowledge, then their beliefs must be identical.
- Priors vs. Posteriors: Priors are the initial beliefs an agent has before seeing evidence. Posteriors are the updated beliefs after considering new evidence. Aumann's theorem shows that rational agents only need to share their posteriors to converge.
- Indirect Speech and Plausible Deniability: People often use hints, innuendo, and euphemisms to make propositions (e.g., bribes, threats, romantic advances) without making them common knowledge, which allows them to deny the intention if the proposition is rejected.
- Coordination vs. Cooperation: A distinction between mutualistic coordination, where all parties benefit by synchronizing their actions (e.g., two people lifting a piano), and altruistic cooperation, where one pays a cost for another's benefit. Both rely heavily on common knowledge.
- Common Knowledge Generators: Mechanisms that create a state of common knowledge. These include explicit public announcements as well as non-verbal signals like mutual eye contact, shared laughter, and blushing, which confirm that information is mutually understood.
Quotes
- At 2:02 - "I know that you know it, and you know that I know you know it, and I know that you know that I know you know it, et cetera, et cetera." - Carroll humorously describes the infinite regress that defines common knowledge.
- At 8:14 - "The difference is in generating common knowledge." - Pinker explains that the key distinction between a direct proposition and a plausibly deniable innuendo lies in whether it establishes common knowledge between the parties.
- At 31:34 - "Reasonable people cannot agree to disagree." - Pinker restates Aumann's Agreement Theorem, which suggests that persistent disagreement among rational people is a paradox that needs explaining.
- At 33:36 - "The kind of surprise in it is they don't have to actually share their evidence... they just have to share their posterior." - Steven Pinker explains the most counterintuitive and powerful aspect of the theorem.
- At 56:22 - "[A chapter called] 'Laughing, Crying, Blushing, Staring, Glaring' on non-verbal displays that I argue are common knowledge generators." - Pinker lists behaviors that serve to create common knowledge without words.
Takeaways
- Social coordination depends not just on what individuals know, but on what they know everyone else knows.
- Persistent disagreement between people often stems from irrationality, different starting assumptions, or a strategic refusal to make beliefs common knowledge.
- Much of social etiquette and indirect communication is a sophisticated dance to manage risk by avoiding the creation of common knowledge.
- Rational argument should be viewed as a cooperative search for truth, where disagreement is seen as new information that should cause you to update your own beliefs.
