Who Benefits from a Supermajority?

Supermajority rules have long been a subject of great interest for both political scientists and general observers of politics alike. Some have argued that a supermajority requirement (especially on core legislation, e.g. amending the constitution) is an effective tool to combat the potential tyranny of the majority and facilitate quality deliberation and more consensual decision-making. On the other hand, opponents of supermajority requirements believe that they create gridlock in the legislature and result in an obscure picture with regards to responsibility in government: voters cannot know who is really behind a certain legislation, thus, democratic decision-making becomes difficult for them. However, analysis on who benefits (whose power is actually increased) has been mostly missing from the literature; most observers simply assume that minority parties benefit from a supermajority requirement. A careful analysis of how a supermajority requirement alters power distribution in an assembly would help us understand the effect of supermajorities better and it would therefore allow for a more sophisticated general evaluation of supermajority rules. This paper aims to evaluate the effect of supermajority requirements on the powers of various players within a given assembly using well-known power indices (Shapley-Shubik and Banzhaf indices). The paper will present this effect via computer simulations, simulating the effect of raising the necessary threshold of successful legislation from a bare majority to a supermajority in various different scenarios. The analysis demonstrates that contrary to intuitive beliefs, the weakest parties in a legislature rarely benefit from a supermajority requirement, while sometimes, even one of the strongest parties can see their power increased by a supermajority requirement. However, minority parties are almost always likelier to be benefactors of supermajority requirements than being harmed by them. The results could stimulate the debate on supermajority rules by presenting their effect in a different light than it has been viewed until now.