 The simplest cases in which conventions arise are ones where we are repeatedly playing a game that is purely co-operative, i.e. the payoffs to each agent are the same, and there are multiple equilibria. In such a case, we may well hope for the equilibrium to persist. At the very least, we will prefer the persistence of the equilibrium to any one person deviating from it. And we will have this preference even if we would prefer, all things considered, to be in some other equilibrium state. In such a case, there may well be a practice of continuing to play one’s part in the equilibrium that has been reached. This is a regularity in action—it involves making moves in the repeated game. Given that everyone else is following the regularity, each agent has a reason to follow the regularity; otherwise it wouldn’t be an equilibrium. But if other agents acted differently, agents would not be interested in following the regularity, since there are alternative equilibria. Because these three conditions are met, Lewis argued that the practice is really a convention, even if there was never any explicit agreement to continue it.