Steven Pinker’s new book When Everyone Knows That Everyone Knows makes a compelling case for common knowledge. His topic is “common knowledge”: things that everyone knows and, crucially, we all know that everyone knows. But then, in chapter eight, which traces the psychological roots of “cancel culture”, everything goes to hell. His argument is that cancel culture is a form of censorship, motivated by “the urge to prevent ideas from becoming common knowledge”. The final chapter covers how we decide whether to keep something semi-private or make it common knowledge.