Majority and Supermajority Rules: Three Views of the Capitol

70 Pages Posted: 27 Apr 2007


The choice of a voting rule for the legislature is as important to public law as the choice between property and liability rules is to private law. This Article provides three models for choosing between majority and supermajority voting rules for the legislature. First, we examine a preference model, familiar from the economics literature, which permits us to explain how transactions costs, including agency costs, affect the choice between majority and supermajority rule. Second, we consider a spatial model used in political science. This model allows us to assess, among other things, the effects on that choice of the status quo as well as important elements of our political system, like agenda setting committees. Finally, we develop an accuracy model, which proceeds on the assumption that legislators genuinely seek to obtain the public interests. We examine under which circumstances majority or supermajority rule best aggregates the judgments of individual legislators.

We come to several significant conclusions. First, supermajority rule works well when special interests use their influence to pass legislation, but works poorly when special interests use their influence to block legislation. Second, supermajority rule works well when the class of bills voted upon by the legislature consists of more socially harmful than socially beneficial legislation - a circumstance we argue is likely to be the norm rather than the exception. Third, we show that an accuracy model provides an insurance rational for supermajority rules. When legislators are more likely than not to discern the public interest less than fifty percent of the time, supermajority rules can provide an efficient form of insurance by reducing the risk of very bad results.

These three different models can be used to select the best voting rule. In this article, we argue that strict supermajority rules are beneficial for entrenching constitutional provisions under both the preference and accuracy models. Supermajority rules are shown to provides a variety of benefits, including to prevent politically divisive entrenchments, to provide insurance against the possibility of bad entrenchments, and to create a veil of ignorance that helps generate constitutional provisions that take account of minority interests. Our analysis helps resolve a fundamental question that has never been satisfactorily answered: why supermajority rules should be used for generating the Constitution.

Keywords: Supermajority rule, entrenchment, constitutional amendment

JEL Classification: H11, H40, H50

Suggested Citation

McGinnis, John and Rappaport, Michael B., Majority and Supermajority Rules: Three Views of the Capitol. Texas Law Review, Vol. 85, p. 1115, 2007, San Diego Legal Studies Research Paper No. 07-100, Northwestern Law & Econ Research Paper No. 07-22, Available at SSRN:

John McGinnis

Northwestern University - Pritzker School of Law ( email )

375 E. Chicago Ave
Chicago, IL 60611
United States
312-503-3235 (Phone)

Michael B. Rappaport (Contact Author)

University of San Diego School of Law ( email )

5998 Alcala Park
San Diego, CA 92110-2492
United States

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