When Everyone Knows That Everyone Knows

Why it’s on the list: Pinker takes one idea from game theory — common knowledge, the difference between everybody knowing a thing and everybody knowing that everybody knows it — and uses it to explain money, authority, taboo, innuendo and the awkwardness of saying the obvious out loud.

Where I saw it: Twice — as a bare Amazon link saved in the note, and again from Kaushik Basu (@kaushikcbasu) on X, November 29, 2025: “Fascinating book by Stephen Pinker, on common knowledge, common sense and salience, in games, everyday life, and war and diplomacy.”

Connections

• Steven Pinker — author.
• Language of Discourse — the portfolio idea this sits closest to: what can and cannot be said out loud, and what changes when it is.
• Game Theory — common knowledge is the formal object this book popularizes.