Steven Pinker on common knowledge... and common delusion

In his new book, Steven Pinker asks us to look at how group knowledge works. Pinker argues that what drives society is knowing that what we know is widely know — in his term, "common knowledge". But what if our beliefs about everyone else's inner thoughts turn out to be wrong?

• Guest: Steven Pinker, experimental psychologist and the author of many popular books on the human mind. His latest is When Everyone Knows that Everyone Knows...: Common Knowledge and the Science of Harmony, Hypocrisy and Outrage
• Producer: Catherine Zengerer and Alex Tighe