Games of Love and Hate

Abstract

A strategic situation with payoff-based externalities is one in which a player’s payoff depends on her own action and others’ payoffs. We place restrictions on the resulting interdependent utility system that generate a standard normal form, referred to as a “game of love and hate.” Our central theorem states that every equilibrium of a game of love and hate is Pareto optimal. While externalities are restricted to flow only through payoffs, there are no other constraints: they could be positive or negative or of varying sign. We examine the philosophical implications of the restrictions that underlie this theorem.