Common Knowledge Principle
Updated 2026-08-10
INTRODUCTION
English translation pending.
CORE DEFINITION
A concept from game theory and epistemic logic, illustrated by the coordinated-attack problem and by the muddled children puzzle. The core proposition is that shared individual knowledge is weaker than common knowledge, because each person may doubt that the others know, so coordination requires the infinite recursion of knowing that others know. The key qualification is that common knowledge is created by public events, such as announcements made in front of everyone at once.
SCAFFOLDING EFFECT
Reduce cognitive load
- Recursion check: ask whether everyone knows, and whether everyone knows that everyone knows. - Public declaration: state the fact openly to all parties at the same time. - Coordination design: build the shared fact into the plan rather than assuming it exists.
Anchor fast decisions
Private knowledge leaves each person uncertain about the others, so each waits for confirmation that never comes without a public event. An announcement made in front of everyone simultaneously closes all the levels of doubt at once, because everyone observes both the message and everyone else receiving it. Once the recursion holds, individual action becomes jointly predictable.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Common_knowledge_(logicverified
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