Steven Pinker: When Everyone Knows That Everyone Knows

Understanding Common Knowledge

• 💡 Common knowledge differs from universal private knowledge; it's not just everyone knowing something, but everyone knowing that everyone else knows it.
• 🎯 The story of the emperor's new clothes illustrates this: people privately knew the emperor was naked, but only when the boy blurted it out did it become common knowledge, changing social dynamics.
• 🧠 Common knowledge can be granted in a stroke through public, conspicuous, or self-evident events, allowing for an implicit understanding of mutual awareness without explicit thought.

Social Impact and Coordination

• 🤝 Common knowledge fundamentally changes social relationships, shifting dynamics from deference to ridicule, as seen with the emperor.
• 🚦 It is necessary for coordination, enabling people to make complementary choices, such as driving on a specific side of the road, because everyone knows the convention.
• 🔑 Many informal social relationships, including friendships, romances, hierarchies, and transactional interactions, are held in place by common knowledge.

Marketing and Network Effects

• 🚀 Common knowledge is crucial for products with network externalities, where the value increases with the number of users, as demonstrated by the Macintosh computer's launch.
• 📺 Apple used the Super Bowl ad in 1984 as a powerful common knowledge generator, making it widely known that the Macintosh was an "insanely great" gadget, rather than detailing its features.
• 📈 The ad's success relied on the audience knowing that many others were also seeing the ad, creating a shared perception of the product's importance and potential widespread adoption.

Common Knowledge and Cancel Culture

• ⚠️ The phenomenon of cancel culture and deplatforming is linked to an urge to prevent certain ideas from becoming common knowledge, especially those perceived to threaten moral norms.
• 🗣️ Social media shaming mobs act as modern-day public punishments, similar to historical pillories, to reinforce norms by making breaches common knowledge and publicly sanctioning them.
• 📚 Even in academia, where open inquiry is valued, there's an urge to deplatform individuals to uphold what are considered moral norms, sometimes at the expense of uncomfortable truths.
• 🚫 The fear that "dangerous ideas" become particularly threatening when they achieve common knowledge can lead to censorship and attempts to suppress their public dissemination.