The Hidden Rules Holding Society Together: Steven Pinker on Common Knowledge
September 9, 2026
AI Summary
5 min read“When the facts change, I change my mind. What do you do, sir?” — a line misattributed to John Maynard Keynes but, as Steven Pinker notes, a very good idea nonetheless. On the Science of Perception Box, cognitive psychologist Steven Pinker joined hosts Heather Berlin and Christoph Koch to explore the hidden structure of common knowledge: the infinite regress of knowing that you know that I know that you know. It is the glue that lets strangers coordinate on the road, friends maintain a relationship without spelling everything out, and markets price assets rationally — and when it breaks, you get awkward silences, stock crashes, and bystanders who don’t act.
What Common Knowledge Actually Means
Common knowledge is not just shared information. We all know the sky is blue, but that is merely mutual knowledge. Common knowledge adds a recursive layer: I know it, you know it, I know that you know it, you know that I know it, and so on upward without end. This infinite structure is what makes coordination possible. Pinker gives the canonical example of driving: it does not matter whether everyone drives on the left or the right, but it matters that everyone drives on the same side and knows that everyone else knows that. A stop sign works because every driver sees the same public signal and knows that every other driver sees it too.
Continue reading the full summary in the app — free to try.
Read Full Summary →Free • No credit card required
Never miss an episode of Science of Perception Box
Get every new episode summarized in your inbox — free, ~5 minutes to read.
No spam. Unsubscribe anytime.
What you'll learn
- 1 (02:59) **Defining Common Knowledge** - Pinker gives the technical definition from philosophy and game theory: infinite mutual awareness.
- 2 (04:31) **Relationships as Coordination Games** - Pinker explains that friendships, hierarchies, and romantic bonds are all coordination games ratified by common knowledge.
- 3 (06:38) **When Common Knowledge Breaks Down** - Miscoordination leads to awkwardness, outrage, or even collisions.
- 4 (08:10) **The Role of Deniability** - Pinker explains how higher-order deniability preserves relationships even when both parties know the truth.
- 5 (09:52) **When Honesty Helps vs. Hurts** - Therapy encourages making private knowledge common, but in functional relationships, tact is the wiser approach.
- 6 (11:34) **Conscious vs. Unconscious Common Knowledge** - Most common knowledge is habitual, but novel situations bring it into conscious awareness.
- 7 (13:14) **Aumann's Agreement Theorem** - Pinker explains the famous theorem: rational people with the same priors cannot agree to disagree.
+ Full timestamped outline available in the app
Guests on this episode
Show Notes
Why do we speak in euphemisms instead of saying exactly what we mean? Dr. Heather Berlin and Dr. Christoph Koch sat down with cognitive scientist and bestselling author Steven Pinker to explore common knowledge — not what everyone knows, but what everyone knows that everyone knows. Get it?
Common knowledge is an awareness of something that is public or “out there” and it has an enormous impact on our social, political, and economic lives. From unspoken rules of flirtation to the fall of the Berlin Wall, Pinker reveals how the social force of common knowledge shapes everything from our most intimate relationships to global financial markets. His work illuminates central ideas of the Perception Box, a framework developed by Elizabeth R. Koch for understanding the forces within us that shape how we see ourselves, relate to others, and move through the world.
Steven Pinker is the Johnstone Family Professor in the Department of Psychology at Harvard University where he conducts research on language, cognition, and social relations. Pinker is the author of thirteen books, including his latest book When Everyone Knows That Everyone Knows… and seminal texts like The Language Instinct, The Blank Slate, and How the Mind Works. His writing has appeared in The New York Times, Time and The Atlantic.
Dr. Heather Berlin is a neuroscientist, clinical psychologist, and Professor of Psychiatry and Neuroscience at the Icahn School of Medicine at Mount Sinai in New York City.
Dr. Christof Koch is Chief Scientist for the Tiny Blue Dot Foundation and the current Meritorious Investigator and former President of the Allen Institute for Brain Science.
Join us for new episodes of Science of Perception Box every Thursday. Follow the show on YouTube, Spotify, Apple Podcasts, Amazon Music, or wherever you get your podcasts.
Love Science of Perception Box? Write us a review on your podcast app, or tell a friend!
Visit unlikelycollaborators.com for more information.
Episode Chapters:
00:00 Why Honesty Fails
02:56 Defining Common Knowledge
06:38 Awkwardness and Innuendo
15:24 Markets and Shared Beliefs
28:44 Bubbles and Bank Runs
31:05 Freedom of Speech
31:49 Berlin Wall Tipping
32:46 Science Versus Assumptions
More from this podcast
Science of Perception Box →