Compromise, Don't Optimize: A Prior-Free Alternative to Perfect Bayesian Equilibrium

Perfect Bayesian equilibrium is the classic solution concept for games with incomplete information, where players optimize under given beliefs over states. We introduce a new concept called perfect compromise equilibrium, where players find compromise decisions that are good in all states. This solution concept is tractable even if states are high dimensional as it does not rely on priors, and it always exists. We demonstrate the power of our solution concept in prominent economic examples, including Cournot and Bertrand markets, Spence's signaling, and bilateral trade with common value.