State ratifying conventions are one of the two methods established by Article V of the United States Constitution for ratifying proposed constitutional amendments. Ratifying conventions have only been used on one occasion, that being for the ratification of the Constitution's 21st Amendment in the year 1933. All other proposed constitutional amendments have been offered to the state legislatures for ratification.
Article V reads in pertinent part (italics added):
The Congress, whenever two thirds of both Houses shall deem it necessary, shall propose Amendments to this Constitution, or, on the Application of the Legislatures of two thirds of the several States, shall call a Convention for proposing Amendments, which, in either Case, shall be valid to all Intents and Purposes, as Part of this Constitution, when ratified by the Legislatures of three fourths thereof, or by Conventions in three fourths thereof, as the one or the other Mode of Ratification may be proposed by the Congress....
Ratification of a proposed amendment has been done by state conventions only once—the 1933 ratification process of the 21st Amendment. The 21st is also the only constitutional amendment that repealed another one, that being the 18th Amendment, which had been ratified 14 years earlier.
As is true for a state legislature when ratifying a proposed federal constitutional amendment, a state ratifying convention may not in any way change a proposed constitutional amendment, but must accept or reject the proposed amendment as written.
The convention method of ratification described in Article V is an alternate route to considering the pro and con arguments of a particular proposed amendment, as the framers of the Constitution wanted a means of sometimes bypassing the state legislatures in the ratification process.
To some extent, the convention method of ratification loosely approximates a one-state, one-vote national referendum on a specific proposed federal constitutional amendment, thus allowing the sentiments of registered voters to be somewhat more directly felt on highly sensitive issues. The theory is that the delegates of the conventions—who presumably would themselves be average citizens—might be less likely to bow to political pressure to accept or to reject a given amendment than would be the case with state legislators. The United States Supreme Court has ruled that a popular referendum is not a substitute for either the legislature or a ratifying convention—nor can a referendum approve of, or disapprove of, a state legislature's, or a convention's, decision on an amendment (Hawke v. Smith, 253 U.S. 221, [1920]).