Common knowledge
Something everyone knows, that everyone knows everyone knows, and so on without end.
Often misread asReading 'common knowledge' as 'everyone knows it', and so treating the higher rungs as pedantry with no practical consequences.
How to see it
Not just that everyone knows, but that there is no last person to find out
Something is common knowledge when everyone knows it, everyone knows that everyone knows it, and so on without end. That is far stronger than everyone happening to know it, and the difference changes what people are able to do.
The checkThe rungs above the first are what let you act on what others will do, and that is where the change in behaviour comes from.
Try itIn the muddy children puzzle every child can already see that at least one child is muddy. Explain why announcing that at least one is muddy still changes what happens. If you cannot, you are still standing on the first rung.
Games that show it
Leads on to
Easily confused with
Sources
- Lewis, D. (1969). Harvard University Press.
- Aumann, R. (1976). Annals of Statistics 4(6), 1236-1239.