The Theory of Political Coalitions

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The Theory of Political Coalitions
Author William H. Riker
Subject Political science
Publisher Yale University Press
Publication date
OCLC 00325635

The Theory of Political Coalitions is a book on positive political theory written by William H. Riker published in 1962. It uses game theory to formalize political theory. In it, Riker deduces the size principle. On its postulates, politicians are proved to form winning, minimal-size coalitions. The work runs contrary to a previous theory that they try to maximize their respective votes. Riker supposes that attracting more votes requires resources and that politicians run to win. A rational politician tries to form a coalition that is as large as necessary to win but not larger.

Minimal size coalitions[edit]

In a five-party system, if, after a general election, this representation is given:

Party A Party B Party C Party D Party E
Number of representatives 5 40 26 25 4 Sum: 100

Three possible winning coalitions are possible:

Party B and C Party B and D Party C and D
40+26=66 representatives 40+25=65 representatives 26+25=51 representatives

If it is now presumed that power will be divided according to strength within the coalition, the parties will prefer the largest relative size within the coalition. The result is that the coalition with C and D is the winning coalition. The largest party is thus kept from power.


The assumption that governments will form on the base of minimal winning coalitions has a poor empirical foundation in Western European multiparty systems.[citation needed]


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