Kristina Stefanova & Michal Lehuta

International University Bremen
14 April 2003
1 Introduction
Coalition Building or “the process of uniting different political actors or organizations in the pursuit of some common goal ” constitutes one of the most fundamental political problems. Political coalitions might consist of individual legislators, parties that want to control of the executive branch, or states united in an international action. In a coalition the actors are fully committed and invest all their resources, such as votes, money or soldiers for the achievement of goals that might not be completely their own. At the end they distribute the gains among them.
Sometimes the participants in a coalition might disagree over what result they expect after organizing the collective action and therefore the question why and in which conditions would coalitions form and survive is a substantial one for predicting and understanding the behavior of various political players.
This essay concentrates mainly on interparty executive coalitions in parliamentary democracies – in other words, parties that seek to control a cabinet responsible to a parliamentary or legislative majority. In the course of describing this process we present the most famous theories on coalition building, which are accompanied with some of the incentives that make parties build certain types of coalitions. Together with showing the political side of this political process, we turn our attention also to the mathematical point of view, which describes parties’ influence in coalition building by a power index. Various people have pondered over the question what makes a party strong in relation to other political players, which lead to the emergence of numerous indices. We look at some of the most important and frequently mentioned in this respect.

When are political coalitions built?
In parliamentary systems that have two dominant parties (Conservatives and Labor in Britain), one of the parties always holds a majority of the seats in the legislature and does not need to build a coalition. In such conditions there are coalitions within the dominant parties, like the one between northern and southern democrats.
In cases where none of the parties has the majority of the parliamentary seats it must necessarily build a coalition. Sometimes the cabinet consists only of representatives of one party although members of other parties support it in debates.