Say know more

There's a science to how we read things - people, situations, moods - as we make our way through each day. A lot of it has to do with what I know you know I know, and so on. In cognitive science, this is called 'common knowledge'. Harvard psychologist Steven Pinker's new book explores the impact of this ability on us - our society, history, culture

- Kanika Sharma

We laugh at the same jokes (usually for the same reasons), blush at innuendo, bow to dictators (at least temporarily), all because of a sense of implicit understanding: ie, common knowledge.

We maintain social contracts such as friendships and kinship, and group together as mobs, based on common knowledge too.

The idea of common knowledge is key to understanding human social constructs, says Steven Pinker, 71, a Canadian psychologist and psycholinguist at Harvard University.

"As a cognitive scientist, I have spent my life thinking about how people think," Pinker adds. "So the ultimate subject of my fascination would have to be how people think about what other people think, and how they think about what other people think they think, and how they think about what other people think they think they think. As dizzying as this cogitation may seem, we engage in it every day, at least tacitly.

Pinker's new book, When Everyone Knows That Everyone Knows, examines the social ramifications of this kind of coalescing, and seeks to untangle how this cognitive ability has impacted history, culture, society.

What do they look like, the mental acrobatics that govern our social world?

Excerpts from an interview.

Common knowledge isn't just "what everyone knows" but "what everyone knows that everyone knows". That sense of acknowledgement is crucial, isn't it?

I open the book with the story of the emperor's new clothes, which I think captures this distinction; because when the little boy points out that the emperor is naked, he isn't telling them anything they don't already know.