The Folk Theorem
Updated 2026-08-08
INTRODUCTION
English translation pending.
CORE DEFINITION
A foundational result in repeated game theory, developed by Drew Fudenberg, Eric Maskin, and others in the 1970s and 1980s. The theorem states that in an infinitely repeated game with sufficiently patient players, any feasible payoff profile giving every player at least their minmax payoff can be supported as a subgame-perfect equilibrium. Cooperation is sustained by credible punishment strategies such as tit-for-tat or grim trigger. The name reflects that the result was widely known before formal publication.
SCAFFOLDING EFFECT
Reduce cognitive load
- Check patience: ask whether the relationship will continue long enough for future losses to matter - Make defection visible: ensure betrayal can be observed reliably and attributed to a player - Define the punishment: agree in advance what happens after a violation so the threat stays credible
Anchor fast decisions
In a one-shot game, defection dominates because the gain is immediate and the cost never arrives. Repetition changes the payoff structure: today's gain is weighed against the loss of all future cooperation, and if the player is patient enough, that loss dominates. The threat of permanent reversion to mutual defection then makes cooperation rational rather than merely moral.
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/Folk_theorem_%28game_theory%29verified
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