A Spatial Voting Model Where Proportional Rule Leads to Two-Party Equilibria.

In this paper we show that in a simple spacital model where the government is chosen under strict proportional rule, if The outcome function is a linear combination of parties' positions, with coefficients equal to their share of seats, only a two-party voting equilibrium basically exists. The two parties taking a positive number of votes are the two wxtremist ones. Applications of this result include an extension of the well-known Alesina and Rosenthal's model of divided government as well as a modified version of Besley and Coate's model of representative democraty.