Strategy-Proofness, Independence of Irrelevant Alternatives, and Majority Rule

We show that strategy-proofness, the Pareto principle, anonymity, neutrality, independence of irrelevant alternatives, and decisiveness uniquely characterize majority rule on any domain of preferences for which there exists a voting rule satisfying these axioms. In our formulation, strategy-proofness includes manipulations by coalitions. However, we demonstrate that the characterization still holds when coalitions are restricted to arbitrarily small size. We also show that when coalitions can manipulate outside the domain, there is an extension of majority rule that satisfies these axioms on any domain without Condorcet cycles. (JEL D72)