Clear+Vivid with Alan Alda

Steven Pinker: When You Know That I Know That You Know…

17 snips
Sep 30, 2025
Cognitive psychologist and bestselling author Steven Pinker dives into the fascinating realm of common knowledge. He explains how understanding what others know can shape emotions, deception, and societal behaviors, using real-life examples like the toilet paper shortage. Pinker discusses the importance of shared experiences in friendships and highlights polarization due to differing knowledge pools. He also touches on laughter as a unifier and the fine art of tactfully correcting others, offering insights into communication dynamics.
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INSIGHT

What Common Knowledge Is

  • Common knowledge is when I know X and you know that I know X, ad infinitum, and it often arises instantly when people observe the same public event.
  • This shared mutual awareness enables coordination at scales from meeting at a cafe to sustaining currency and preventing bank runs.
INSIGHT

Coordination Needs Mutual Belief

  • Common knowledge is necessary for coordination because each person's action depends on knowing others will act too.
  • Without mutual awareness both people may hesitate and coordination fails, even for simple meetups.
ANECDOTE

Carson Joke Caused A Real Shortage

  • Johnny Carson joked about a toilet-paper shortage in 1973 and viewers rushed to buy paper, creating an actual shortage.
  • The joke worked because many knew others were watching Carson, generating common expectation and mass behavior.
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