We have seen that actors cannot credibly commit to cooperation in a repeated prisoner’s dilemma if the game has a definite ending. But can they cooperate when their interaction will go on indefinitely?
- Grim trigger is a policy of tough love; you start by cooperating and continue to cooperate as long as everyone has cooperated in the past. If someone has defected, then you defect forever.
- The threat of forever conflict keeps everyone cooperating today as long as everyone cares enough about the future.
- This is a critical result from The Evolution of Cooperation, one of the most influential political science books ever written.