  Lewisian convention is a special case of Nash equilibrium, the central idea behind modern game theory. An assignment of strategies to players is a Nash equilibrium iff no agent can improve his payoff by deviating unilaterally from it. An equilibrium is strict iff each agent decreases his payoff by deviating unilaterally from it. Intuitively, a Nash equilibrium is a “steady state”, since each player behaves optimally, given how other players behave. In this sense, Nash equilibrium “solves” the strategic problem posed by a game, so it is sometimes called a “solution concept”. However, Lewisian convention goes well beyond Nash equilibrium. In a Lewisian convention, everyone prefers that everyone else conform if at least all but one conform. Equilibria with this property are sometimes called coordination equilibria.