Supermajority
A pass threshold above half, usually two-thirds, used where a bare majority is too thin a basis.
A method is only real when its numbers are written down beside it — what share passes, how many must take part, who may object and on what grounds. Ask a community which method it used for its last three decisions. If the answer is the same for all three, either the community is very small or the method is aspirational.
A supermajority is any pass threshold above half. In community practice it is almost always two-thirds, occasionally three-quarters, and it is reached for when a bare majority feels like too thin a basis for what is being decided.
The instinct is sound. Twenty-one against twenty is a decision under majority rule and it is not a settled question, and communities that carry contentious changes on margins like that tend to relitigate them for years. Raising the bar means that what passes has real weight behind it.
What it costs, exactly
Raising the threshold does not only make bad decisions harder to pass. It makes all decisions harder to pass, and it hands a determined third of the group a standing veto over change.
That is not a criticism, it is the mechanism. A two-thirds rule is a deliberate transfer of power from the majority to any sufficiently large minority, and whether that is protection or paralysis depends entirely on what is being protected. Applied to the community’s founding purpose, it is exactly right — a purpose that thirty-five per cent of members actively oppose is not a shared purpose. Applied to the annual budget, it means a third of the group can starve the community by declining to agree to anything.
This is the trade-off Buchanan and Tullock formalised in The Calculus of Consent (1962): as the required share rises, the cost of reaching a decision rises and the cost of being overruled falls. There is no rule that is best for everything, only a rule that is best for a given class of decision — which is the argument for decision tiers rather than a single number.
The details that decide it
Two-thirds of what? Of everyone eligible, or of those who voted, or of those who voted either way with abstentions set aside? These produce genuinely different outcomes, and a group that has not written down which one it means will discover the ambiguity on the day it matters most.
A threshold also does nothing on its own without a quorum . Two-thirds of six people is four.
Related terms
The minimum number of members who must take part before a result counts at all.
Sorting decisions by what they cost to get wrong, and giving each class its own method and timeline.
A decision method requiring the agreement of all participants. Powerful for trust, slow under scale and fatigue.