Tit-for-Tat

Game Theory · Axiom Academy

Unit 4: Repeated Games - A Simple Yet Powerful Strategy for Cooperation Tit-for-Tat (TFT) is a strategy for repeated games that follows two simple rules: Round t ≥ 2: Do whatever your opponent did in round t-1 In other words: start nice, then mirror your opponent's last move. If they cooperated, you cooperate. If they defected, you defect. Watch how this plays out in a repeated Prisoner's Dilemma: 2. Key Properties of Tit-for-Tat Tit-for-Tat has four important properties that explain its success: Nice: Never defects first (always starts with cooperation) Retaliatory: Punishes defection immediately in the next round Forgiving: Returns to cooperation as soon as the opponent does Clear: Easy to understand and predict, allowing opponents to learn These properties make TFT effective at encouraging mutual cooperation while still protecting against exploitation. Let's see how these properties work in action: Political scientist Robert Axelrod famously organized computer tournaments in the 1980s where strategies competed in repeated Prisoner's Dilemma games. Tit-for-Tat, submitted by game theorist Anatol Rapoport, won both tournaments despite being one of the simplest strategies. The animation below shows TFT's performance pattern across different types of opponents: 4. Tit-for-Tat vs. Grim Trigger Another well-known strategy is Grim Trigger , which cooperates until the opponent defects once, then defects forever after. The key difference is forgiveness :

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