The Internal Politics of Parties: The Law of Curvilinear Disparity Revisited

One of the few efforts to link systemic and organizational determinants of party strategies is provided by what John May dubbed the ‘law of curvilinear disparity’. According to this law, voters, party activists and leaders have necessarily divergent political ideologies. These systematic differences are attributable to the activists' motivations and the constraints of party competition. This paper argues that the law is empirically valid only under distinctive behavioural, organizational and institutional conditions which are not specified in its general formulation. Thus, the law is only a special case in a broader theory reconstructing the interaction between constituencies, intra-party politics and party competition. This alternative theory is partially tested with survey data from party activists in the Belgian ecology parties Agalev and Ecolo.