We experimentally study the effect of a third person enforcement on a one-shot prisoner’s dilemma game played by two persons, with whom the third person plays repeated prisoner’s dilemma games. We find that when the third person can observe these two persons’ play, the possibility of the...

We theoretically study the effect of a third person enforcement on a one-shot prisoner’s dilemma game played by two persons, with whom the third person plays repeated prisoner’s dilemma games. We find that the possibility of the third person’s future punishment causes them to cooperate in...