Coalition Formation in Centralized Policy Games

In this article a theory is presented that deals with the entry of coalitions in political systems. This theory, which is formulated in game theoretical terms, is called the theory of power excess coalitions. It is based on the behavioral assumption that each player strives to form a coalition in which the player can maximally control the internal opposition. Three variations of the theory are presented. The first variation deals with the entry of coalitions in political systems in which policy does not figure. In contrast, in the other two variations, policy positions will play an essential role. A political system will then be modelled as a so-called centralized policy game. In these policy models, the notion of `center' and the related notions of `left' and `right' are basic. The non-policy variation will lead to Riker's minimum size principle (Riker, 1962; Riker and Ordeshook, 1973); the other variations each lead to a modified policy version of this principle.