"Plurality Mechanisms, Virtual Implementation, and Condorcet-Decisiveness"

We investigate implementation of social choice functions as mappings from states to lotteries under complete information. We assume that for every agent, any pair of distinct states induces distinct preferences. A social choice function is called Condorcet-decisive if it always enforces the Condorcet winner among its range. We introduce plurality mechanisms, where each agent makes a single announcement and the lottery associated with the opinion announced by the largest number of agents is enforced. We show that a social choice function is virtually implementable via plurality mechanisms combined with constrained random dictatorship, if and only if it is Condorcet-decisive.