经由政党的实施

We address the implementation of public policies (alternatives) when the feasible set is unknown to the planner. The implementing agents are the political parties, who know the feasible set. They care about the implemented alternative, which reflects their ideology, and their share in parliament and office. They face a mechanism that, given the alternatives proposed by all parties, asks the voters to rank them and determines the chosen alternative and the shares in parliament and office. We identify conditions on parties’ preferences that guarantee the socially optimal policy is the outcome of the unique pure strategy Nash equilibrium of the electoral game played by the parties. The existence of the equilibrium does not require any assumptions about the parties’ ideology. To ensure uniqueness, shares must prevail over ideology: office or parliamentary shares in two-party systems, and strictly office shares in systems with more than two parties.