The bargaining process by which political parties negotiate to build a governing coalition after an election produces no single-party majority, deciding which parties join, how cabinet portfolios are divided among them, and what policy commitments bind the resulting government. The dominant early formal theory, developed by the political scientist William Riker in 1962, held that rational parties would form the smallest coalition able to command a legislative majority, a minimum winning coalition, since any larger coalition dilutes the spoils of office among more partners than winning requires. Later scholarship found many real coalitions are not minimum winning at all, and added ideological proximity between partners and the practicalities of dividing portfolios as further explanations that Riker's original size-based theory left out.
Facts
Origin YearThe year William Riker's The Theory of Political Coalitions formalized the minimum-winning-coalition model as a subject of political science. Coalitions have been formed under parliamentary systems since long before any formal theory described them, so this date records the origin of the theory, not the practice. Founding ContextFormal theoretical study advanced significantly with William Riker's 1962 book The Theory of Political Coalitions, which introduced the size principle and the concept of minimal winning coalitions. 1 Connections
Associated With
Italy, Countries Why this is disputed. Whether Italy's history of frequent, often ideologically disparate coalition cabinets is better explained by Riker's minimum-winning-coalition theory or by later policy-proximity and portfolio-bargaining theories is a live dispute among coalition scholars. Italy's postwar record is cited on both sides: its coalitions have rarely been minimum winning in Riker's strict sense, which some read as evidence against the theory and others read as the predictable result of Italy's especially fragmented multiparty system.
Source Coalition Formation (SAGE Encyclopedia of Political Science)
Sources
1. National Academies Press: Riker Biographical Memoir
National Academy of SciencesRiker biographical chapter
In The Theory of Political Coalitions, Riker deduced the size principle, introducing the idea of minimal winning coalitions in the study of electoral and legislative politics.
Building a Positive Theory of Politics section
In The Theory of Political Coalitions, Riker deduced the size principle, introducing the idea of minimal winning coalitions
View the Source Coalition Formation (SAGE Encyclopedia of Political Science)
Dissenting Readings (1 dissenting reading)
Description
William Riker's 1962 Theory of Political Coalitions holds that rational parties form the smallest coalition that can command a majority (the "size principle"), since a smaller winning coalition means fewer partners to share power and spoils with. Anthony Downs, working from a vote-maximizing model of party behaviour, argued parties are driven less by the arithmetic of minimal winning size than by policy-seeking and vote-seeking incentives that can produce larger or ideologically narrower coalitions than Riker's model predicts. A substantial subsequent literature on coalition formation and government stability grew directly out of this Riker-Downs disagreement.
A dissenting reading, from Anthony Downs's vote-maximization critique of Riker's minimal-winning-coalition theoryNational Academies Press: Riker Biographical Memoir, National Academy of Sciences
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