Double majority

A double majority is a voting system which requires a majority of votes according to two separate criteria. The mechanism is usually used to require strong support for any measure considered to be of great importance. Typically in legislative bodies, a double majority requirement exists in the form of a quorum being necessary for legislation to be passed.

Australia
In Australia, constitutional changes must be passed at a referendum in a majority of states (4 of the 6), and by a majority of voters nationally. Prior to 1977, the votes of citizens in the Northern Territory and the ACT did not affect the national or state-based count. After a Constitution Alteration put to referendum in 1977 and given vice-regal assent on 19 July 1977, Territorial votes contribute towards the national majority, but the Territories themselves do not count towards the majority of states. An earlier referendum in 1974, where the same proposed change had been bundled with a lowering of the required number of states to a half (3 of the 6) instead of a majority, had been defeated.

Canada
Since the patriation of the Canadian constitution in 1982, thorough amending formulae for the constitution were adopted. Per the Constitution Act, 1982, many amendments can be passed only by the Parliament of Canada and a two-thirds majority of the provincial legislatures, those provinces together representing at least 50% of the national population-–this is known as the 7/50 formula (as there were and are 10 provinces, so 7 constitutes a two-thirds majority). Additionally, a province can explicitly choose to dissent to an amendment that "derogates from the legislative powers, the proprietary rights or any other rights or privileges of the legislature or government of a province", in which case it does not apply in that province even if passed. Though not constitutionally mandated, a referendum is also considered to be necessary by some, especially following the precedent established by the Charlottetown Accord in 1992.

However, there are some parts of the constitution that can be modified only by a vote of all the provinces plus the Parliament of Canada; these include changes to the composition of the Supreme Court of Canada, changing the process for amending the constitution itself, or any act affecting the Canadian monarch or Governor General.

European Union
In the European Union, double majority voting replaced artificial voting weights for votes requiring a qualified majority in the Council of the European Union following implementation of the Treaty of Lisbon. A qualified majority requires 55% of voting EU member states, representing at least 65% of the population of voting members for a European Commission proposal to be approved. This increases to 72% of voting members states, representing at least 65% of the EU population of voting members should the proposal originate from a member state. Proposals can be blocked should a qualified majority of at least four Council members representing more than 35% of the EU population be formed.

Finland
Changing the constitution of Finland requires that a simple majority of the sitting Parliament vote in favor of the amendment. The amendment is postponed until the next general election. The next parliament may finally vote to ratify the amendment but by a two thirds of the MPs. Thus, a double majority of two different parliaments is usually required to pass constitutional amendments. An expedited process may however be entered if five sixths of the sitting parliament vote to declare an amendment urgent. Then, a two-thirds majority of the current parliament may ratify an amendment using the expedited process.

Northern Ireland
Under the terms of the Belfast Agreement, if 30 members or more request it, a measure may be put to a "cross-community vote" which requires a majority from both the Nationalist and Unionist camps.

Philippines
In the 2019 Bangsamoro autonomy plebiscite, for a place to join the Bangsamoro, it is required to have a majority for inclusion both in the place that is petitioning to be included, and from the rest of the larger entity it is originally included. For example, for the six towns from Lanao del Norte petitioning to join, a majority both from the town itself and from the rest of Lanao del Norte should be attained. Each of the six towns overwhelmingly voted for inclusion, but a majority from the rest of Lanao del Norte rejected the towns joining the Bangsamoro, leading to the towns not being included. Meanwhile, 63 of the 67 barangays (villages) in Cotabato voted for inclusion and got consent from their mother towns to join. One barangay rejected inclusion but was allowed by its mother town to join, while three barangays voted for inclusion but were rejected by their mother towns from joining; these four barangays did not join the Bangsamoro. Finally, Isabela City rejected to join, but was allowed by its mother province Basilan to join; it was also not included in the Bangsamoro.

Romania
In Romania, a national referendum is considered valid only if at least 50% plus one of the registered voters cast their ballot. For a valid referendum, the outcome is determined by a simple majority of valid votes cast. The whole process thus involves a double majority in form of a quorum.

A controversial amendment to the referendum law arose during the 2012 political crisis and allowed for an exception to be made in case of a referendum regarding the impeachment of the President. The original law, which required a double majority for impeachment, was modified by governmental emergency decree to circumvent the quorum requirement. This would have resulted in a successful impeachment of the President in the following referendum. The referendum was, however, subsequently invalidated by the Constitutional Court, the body responsible for overseeing the whole process, putting an end to the crisis.

Sudan
The independence referendum for South Sudan required 51% of the vote and 60% turnout.

Switzerland
In Switzerland, the passing of a constitutional amendment by popular vote requires a double majority; not only must a majority of people vote for the amendment but a majority of cantons must also give their consent. This is to prevent a larger canton from foisting amendments onto the smaller ones and vice versa.

United States
Double majority is used in the United States for some initiative or referendum votes on issues such as a tax levy or bond. Essentially, a double majority standard applies a two-part test to a vote outcome before a measure is passed: If the answer to either of these questions is No, the measure fails.
 * Did a majority of registered voters turn out for the election?
 * Did votes in favor outnumber votes against, by the required margin?

This mechanism is used to prevent a small group from passing spending measures that affect the entire population in order to support their pet causes, especially at an election expected to have low voter turnout. Double majorities are also frequently used in municipal annexations, wherein majorities of both the residents in the annexing territory and the territory to be annexed must support the annexation. A similar rule exists for adopting metropolitan government in Tennessee, where the referendum must pass both inside and outside the principal city.