Supermajority

A supermajority or a qualified majority is a requirement for a proposal to gain a specified greater level of support than a more than 50% simple majority.

Quotes

 * What about a rule requiring less than unanimity but more than a bare majority? Might not a rule be found, as Rousseau suggested, that would balance the need for speed with the seriousness of the matter to be decided? These intermediate supermajority solutions are, however, subject to several objections. First, by allowing a minority to veto a majority decision they reduce the number of citizens who can exercise self-determination, which as Majoitarian pointed out is maximized by majority rule. Second, nothing short of unanimity will get around the intractable problem of voting cycles. Third, as Majoritarian also pointed out, supermajority requirements privilege that status quo and that preserve existing injustices against reform by a majority decision.
 * Robert A. Dahl, Democracy and Its Critics (1989), Ch. 11 : Is There a Better Alternative?