How to Amend a Constitution? Model, Axioms, and Supermajority Rules
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A self-governed community or society must have rules by which group decisions are made. These rules are often codified by a written constitution that specifies not only the rules by which decisions are made, but also the means by which these rules can be changed, or amended. One of the defining characteristics of constitutions is entrenchment, or the difficulty of enacting changes. Too little entrenchment means a constitution has little force behind it and can change frequently. Excessive entrenchment can be similarly destabilizing if it frustrates too many of its constituents, and can undermine the collective will. We take a stylized model of constitutions that use a fixed amendment rule to adjudicate amendments to a constitutionally designated decision rule to be used for decisions. We focus on the the most common form of entrenchment, delta-supermajority rules, which accept a proposal over the status quo if more than a 1/2 + delta fraction of the voters support it. Under this model we introduce desirable axioms for amendments, and design constitutions with amendment procedures based on these axioms to balance the degree of entrenchment, maintain stability, and avoid frustrating people.
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