Common Knowledge
Updated 2026-09-10
INTRODUCTION
English translation pending.
CORE DEFINITION
Common knowledge obtains in a group when not only does everyone know A, but everyone knows that everyone knows A, and knows that everyone knows that everyone knows A, in an infinite recursion. Mutual knowledge, by contrast, requires only that each person knows A, without each knowing that others know it. Robert Aumann gave a set-theoretic characterization, and David Lewis linked the notion to convention.
SCAFFOLDING EFFECT
Reduce cognitive load
- Judge coordination: analyze whether each side knows that the other knows, to see if cooperation can occur. - Design communication: turn private knowledge into public announcement so that collective action becomes possible. - Trace miscoordination: separate everyone knows from common knowledge to find the root of failed teamwork.
Anchor fast decisions
Common knowledge works through the coordinating function of higher-order information: only when you know that I know, and that this is shared, can agents treat expectations of others' actions as a common basis and select the same equilibrium in a coordination game. Aumann characterizes it via common partitions of public events, and Lewis explains its generation through conventions and what is openly observed.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- plato.stanford.eduhttps://plato.stanford.edu/entries/common-knowledge/verified
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