Pinker illustrates his arguments with piquant little dialogues, some of them worthy of Laing (“You hang up first”. The central theme is simply expressed: all acts of communication occur against a background of intricate, recursive assumptions (I know x; you know that I know x; I know that you know that I know x; you know that I know that you know … ad infinitum). What Pinker calls “common knowledge” is both what makes intelligible exchange possible and what complicates it. Pinker directs his strongest polemic at those who deliberately seek to suppress or limit common knowledge in order to protect what is thought to be a vulnerable or fragile social consensus. If you do not have an account, we will create a guest account for you on theguardian.com to send you this newsletter.