This post is part of Fifty Shades of Republic, a series of overviews of US political institutions at the state level
While the Federal Constitution is arguably the world’s oldest national constitution, the states were the ones that began the practice of having ‘written’ constitutions – entrenched laws with a higher status than regular laws, establishing the main features of the system of government. Since I’ve been doing some work on constitution amendment rules (of both national and US state constitutions) for my dissertation, I thought I’d do this topic next (it is also closely related to the topic of a podcast I am currently preparing for Leviathan’s Couch).
The amendment procedure has far-reaching effects. John Burgess, one of the 19th century pioneers of political science, argued it to be the most important part of a constitution. Constitutional amendment procedures entrench written constitutions, making them harder (or, at least, different) for politicians to change than regular laws. Entrenchment is meant as a means to provide the system of government with stability and to protect basic rights from change by temporary majorities. However, it also often leads to the constitutional entrenchment of various policy measures that do not pertain to the state’s basic institutions, either as a result of opportunistic coalitions seeking to protect legislation from future change or because restrictive provisions in the constitution make the incorporation of contradictory provisions into the constitutional text the easiest way of passing certain policies. Lastly, entrenchment is also an important driver of the power of the judiciary (to whom enforcement of the constitutional hierarchy is delegated).
Most US states have two or more of the following tracks to initiating a constitutional amendment: by the legislature, by a voter initiative, or by constitutional convention. The final stage is almost always ratification by voters in a referendum.

Proposal
Supermajorities – 28 states today require a supermajority for passage in the state legislature. 22 only require regular majorities (simple or absolute) before going to referendum.
Of those only requiring approval by one legislature:
- 10 states (turquoise) require a majority in both houses
- 9 states (blue) require 3/5 in both houses
- 16 states (dark blue) require 2/3 in both houses.
Of those requiring intervening elections:
- 11 states (pink) require a majority in both houses before and after the elections
- 3 states (red) require a 2/3 supermajority at one stage but not both. In Tennessee, the votes after the election must be by 2/3 in both houses; in Vermont, the amendment must be supported by 2/3 before the election, although only in the state Senate. South Carolina (dark red) requires 2/3 in both houses, after which the amendment is put to the voters at the following election. The referendum, however, is not final; it the amendment is approved, the newly-elected legislature must ratify it by majority vote in both houses.
- Delaware (green) requires 2/3 in both houses both before AND after the intervening election, with no referendum requirement.
Intervening elections – 15 states require approval by two legislatures separated by intervening elections (shown on the map in various shades of red). A few of those states allow this requirement to be bypassed by supermajority support in the legislature (shown by a blue asterisk, with the shade of blue corresponding to the required supermajority (in states without intervening election requirement – see below) – only exception being Connecticut, where ¾ is needed to bypass the intervening election requirement). Since main idea behind this institution is often said to have been to allow voters input on constitutional amendments through the election process, many states that had this feature in earlier constitutions removed it when introducing ratification of amendments by referendum, but many have kept it nonetheless.
Initiative – Currently, 17 states allow voters to propose amendments to referendum by petition (indicated by a capital letter I on the map). The exact signature requirements vary widely from state to state. This provision originated in the Progressive era, although a few states introduced it later.
Ratification
Referendum – the referendum requirement became a near-universal feature by the time of the Civil War. In states that did not have it to begin with, it often replaced requirements for intervening elections and/or assembly supermajorities. Referendums today require a majority to ratify in almost all states; the denominator is sometimes simply the number of valid votes on the respective amendment question, but in some states it is the more demanding number of people voting at the election, so that ballots left blank count as a ‘no’. In a few states a supermajority is required for some or all amendments, e.g. in Colorado, 55%, in New Hampshire, 2/3.
Legislative vote – today, Delaware (in green) is the only state not to require voter approval for constitutional amendments – the second round of 2/3 vote in the legislature makes an amendment part of the constitution. As noted above, South Carolina does require voter approval, but an amendment approved by voters is still subject to a final (majority) vote by both houses.

Legislative convention call – In 6 states, the legislature can directly order the election of a constitutional convention (without needing voter approval) by either majority (light green) or supermajority (green) in both houses.
Legislative convention proposal – In 30 states, a convention call by the legislature must be ratified by voters. In some states the proposal can be made is by a majority (light purple), in others by supermajority (purple) in both houses. In Pennsylvania, there is precedent for this, even though the state constitution does not provide for it.
Ambiguous, referendum required – In 3 states, the constitution requires the summoning of a constitutional conventions to be approved by voters, but is silent on whether the legislature can propose this (pale blue).
Automatic ballot question – In 14 states, a convention proposal must be placed before voters at least once every certain number of years. This is indicated on the map by the specific number of years in each case.
Initiative – In 17 states, voters can initiate the summoning of a convention, either by the constitution’s explicit provision or by virtue of the possibility of proposing one using the procedure for initiating amendments. This is indicated by a capital letter I on the map.
No provision – in 11 states, the constitution does not provide for the calling of a constitutional convention (grey) nor does the state have any established practice. De facto, each of these state legislature could summon a convention by means of the regular amendment procedure.
Constitutions are usually silent on the conditions for conventions’ proposals to be made or ratified, with the exception of requiring a referendum as on ‘regular’ amendments. A few noteworthy exceptional provisions include Illinois’ requirement for 60% voter approval for any kind of convention proposal to be successful, New Hampshire’s requirement for amendments to be proposed by 3/5 vote of the convention, and Minnesota’s requirement for 60% voter approval to ratify any amendment proposed by a convention.
International comparisons
While explicit constitutional recognition of a convention route is somewhat unusual, state constitutions’ regular amendment procedures in state constitutions are very comparable to those of many national constitutions around the world. Here are a few essentially exact parallels:
- Minnesota, Rhode Island – Ireland (majority + referendum)
- Texas, Maine – Japan, Romania (2/3 + referendum)
- Oregon, Arkansas – Switzerland (majority + referendum, initiative option)
- New York, Virginia – Denmark (majority + election + majority + referendum)
However, there are some clear differences, as well. Around the world, amendment procedures that do not require direct voter approval are far more common than among US states. In fact, most democracies today do not require a referendum at all. Meanwhile, many other democracies have a referendum as just one potential method of ratification – an alternative to a legislative supermajority (so not an absolute requirement), or required for some changes but not all.
Meanwhile, it’s internationally rare for referendums to be combined with an intervening election requirement (especially when further combined with supermajorities). I just gave the example of Denmark, but I think it’s the only one, at least for the main amendment procedure; Spain has a procedure for 2/3 legislative vote before and after an election, followed by a referendum, but this procedure is reserved for amendments to the chapters on fundamental rights and the Crown.