A simple sufficient condition for strong implementation

In an important step forward Maskin (1977) showed that two properties −Monotonicity and No Veto Power − form a sufficient condition for Nash implementation when conjoinet. In contrast to the vast literature that followed, this characterization has two big advantages: First, it is often easy to verify, and second, it has an elegant and simple interpretation. However, there does not exist a similar condition for social choice correspondences that are implementable in strong equilibrium. All existing characterizations are either hard to verify or apply only in comprehensive preference domains. In this paper we improve the situation by give such a condition called the Axiom of Sufficient Reason and show that this is a practical tool in some important applications. JEL Classification: C72; D78