Article Five of the United States Constitution describes the process by which the constitution may be altered. Amendments to the Constitution may be proposed by the United States Congress or by a national convention assembled at the request of at least two-thirds of the legislatures of several states. This means that two thirds of the members of each house of Congress must vote in favor of the amendment. An amendment must then be ratified by either the legislatures of three-fourths of the several states or by or ratifying conventions in three fourths of the states. With the current make up of the United States, if thirteen or more states disapprove of any amendment they may block its ratification.
There are two methods described in Article V to make amendments. By the first method, Congress adopts and the states ratify the amendment. Amendments can take place by a vote of two-thirds of both the House of Representatives and the Senate followed by a ratification of three-fourths of the various state legislatures. Ratification by thirty eight states (three-fourths) would be required to ratify an amendment today. This method of amendment is the only one used to date. The second method is one in which the States propose an amendment at a convention called for this purpose by two thirds of the state legislatures. Later on three-fourths of the state legislatures must ratify the proposed amendment.
The Constitution is silent on the issue of whether a state should be allowed to rescind its ratification of pending amendments. This question has not yet been resolved. However, once the ratification process is complete, a withdrawal would have no effect.
Article V of the Constitution reads: “Amendments to this Constitution … shall be valid to all Intents and Purposes, as part of this Constitution, when ratified by the Legislatures of three fourths of the several States, or by Conventions in three fourths thereof.” After the required numbers of states ratify an amendment it becomes “valid to all Intents and Purposes.” A state cannot make an amendment invalid after it has become valid. The only way to undo an amendment is to make another amendment. Additionally, it was held in Dillon v Gloss that congress can fix a reasonable time within which a proposed amendment must be ratified.
The main purpose of the amending process described in Article V of the Constitution is to permanently protect the people of the nation from unreasonable amendment proposals and ratifications.
 USCS Const. Art. V
 256 U.S. 368 (U.S. 1921)