There are essentially two ways spelled out in the Constitution for how to enact an amendment. One has never been used.
- The first method is for a resolution to pass both houses of Congress by a two-thirds majority vote in each. Once passed, the bill goes on to the states for ratification. This is the route to success taken by all current amendments. Congress will normally puta time limit (typically seven years) for the amendment to be ratified by the states (for example, the 21st and 22nd). Three-quarters of the states must ratify for the amendment to become law.
- The second method prescribed is for a national Constitutional Convention to be called by two-thirds of the legislatures of the states, and for that Convention to propose one or more amendments. Any amendments would then need to be ratified by either three-fourths of the state legislatures or state conventions. No such Constitutional Convention has ever taken place. There is considerable dispute in political science circles about what kind of changes it would bring about.
No matter which of the two allowed means of initiating an amendment is used, the amendment must be ratified by three-fourths of the states. There are two permissible methods by which states may ratify - via a vote by all the state legislatures or by a vote of newly convened individual state conventions. The text of the amendment usually will specify which method. Only one amendment, the 21st, specified the state convention route.
In any case, ratification by either the legislatures or by state conventions is by simple majority vote.
In sum, the Constitution spells out four paths for an amendment:
• Proposal by convention of states, ratification by state conventions (never used)
• Proposal by convention of states, ratification by state legislatures (never used)
• Proposal by Congress, ratification by state conventions (used once)
• Proposal by Congress, ratification by state legislatures (used all other times)
Notably, at no point does the President have a role in the formal amendment process (though he/she would be free to make his/her opinion known). A President cannot veto an amendment proposal, nor a ratification. This point is clear in Article 5, and was reaffirmed by the Supreme Court in Hollingsworth v Virginia (3 US 378 ):