ABSTRACT
Theoretical models of party competition often treat political parties as ‘unitary’ actors. Real political parties are collectivities – coalitions of political agents who have something in common, at the very least a party label. In this important sense, political parties are endogenous outputs of political competition as much as inputs to it. This means we must explain why, in practice, members of a political party often behave in a cohesive and/or disciplined way so that, to an outside observer, the party behaves ‘as if’ it is a unitary actor.
