Most decisions need just more than half. But for the weightiest acts, changing the Constitution, removing a president, overriding a veto, the framers demanded much more, a supermajority, so the gravest choices need broad agreement.
A supermajority is a required voting margin larger than a simple majority of more than half. Common thresholds are two-thirds or three-fifths. It raises the bar for certain decisions, requiring broad consensus rather than a bare edge.
The Constitution reserves it for the highest stakes. It takes a two-thirds vote to override a presidential veto, to propose a constitutional amendment, to ratify a treaty, to expel a member of Congress, and to convict an impeached official. These are not ordinary decisions, so they need extraordinary agreement.
The logic is protective. By requiring a supermajority, the framers ensured that the most consequential and hardest-to-reverse actions could not be taken by a slim, possibly fleeting, majority. Such choices must rest on wide and durable support.
It also appears in the Senate's rules. The modern filibuster effectively requires a three-fifths supermajority, sixty votes, to end debate on most legislation, which is why so many bills need far more than a simple majority to pass.
