Constitutional convention (political custom)

A constitutional convention is an informal and uncodified procedural agreement that is followed by the institutions of a state. In some states, notably those Commonwealth of Nations states that follow the Westminster system and whose political systems derive from British constitutional law, most government functions are guided by constitutional convention rather than by a formal written constitution.
In these states, actual distribution of power may be markedly different from those the formal constitutional documents describe. In particular, the formal constitution often confers wide discretionary powers on the head of state that, in practice, are used only on the advice of the head of government, and in some cases not at all.
Some constitutional conventions operate separate from or alongside written constitutions, such as in Canada since the country was formed with the enactment of the Constitution Act, 1867. In others, notably the United Kingdom, which lack a single overarching constitutional document, unwritten conventions are still of vital importance in understanding how the state functions. In most states, however, many old conventions have been replaced or superseded by laws (called codification).
Definitions.
The term was first used by British legal scholar A. V. Dicey in his 1883 book, "Introduction to the Study of the Law of the Constitution". Dicey wrote that in Britain, the actions of political actors and institutions are governed by two parallel and complementary sets of rules:
A century later, Canadian scholar Peter Hogg wrote,
Origins.
Constitutional conventions arise when the exercise of a certain type of power, which is not prohibited by law, arouses such opposition that it becomes impossible, on future occasions, to engage in further exercises of this power. For example, the constitutional convention that the Prime Minister of the United Kingdom cannot remain in office without the support of a majority of votes the House of Commons is derived from an unsuccessful attempt by the ministry of Robert Peel to govern without the support of a majority in the House, in 1834–1835.
Enforceability in the courts.
Constitutional conventions are not, and cannot be, enforced by courts of law. The primary reason for this, according to the Supreme Court of Canada in its 1981 Patriation Reference, is that, "They are generally in conflict with the legal rules which they postulate and the courts may be bound to enforce the legal rules." More precisely, the conventions make certain acts, which would be permissible under a straightforward reading of the law, impermissible in practice. The court ruled that this conflict between convention and law means that no convention, no matter how well-established or universally accepted, can "crystallize" into law, unless the relevant parliament or legislature enacts a law or constitutional amendment codifying for a convention at which must specify request and consensus' for enactment. This principle is regarded as authoritative in a number of other jurisdictions, including the UK.
Some conventions evolve or change over time. For example, before 1918 the British Cabinet requested a parliamentary dissolution from the monarch, with the Prime Minister conveying the request. Between 1918 and 2011, Prime Ministers requested dissolutions on their own initiative, and were not required to consult members of the Cabinet (although, at the very least, it would have been unusual for the Cabinet not to be aware of the Prime Minister's intention).
However, conventions are rarely ever broken. Unless there is general agreement on the breach, the person who breaches a convention is often heavily criticised, on occasions leading to a loss of respect or popular support. It is often said that "conventions are not worth the paper they are written on", i.e., they are unenforceable in law because they are not written down.
Examples.
Australia.
No convention is absolute; all but one (the second) of the above conventions were disregarded in the leadup to or during the constitutional crisis of 1975.
Ignoring constitutional conventions does not always result in a crisis. After the 2010 Tasmanian state election, the Governor of Tasmania rejected the advice of his Premier to appoint the leader of the opposition as Premier because he felt the advice was tendered in bad faith. The Premier went on to form a new government.
New Zealand.
There is a convention that the Prime Minister of New Zealand should not ask for an early election unless he or she is unable to maintain confidence and supply. By the 1950s, it had also become a convention that elections should be held on the last Saturday of November, or the closest date to this range as possible. There are several times when these conventions have been broken and an election has been held several months earlier:
Norway.
Because of the 1814 written constitution's pivotal role in providing independence and establishing democracy in the 19th century, the Norwegian parliament has been very reluctant to change it. Few of the developments in the political system that have been taking place since then have been codified as amendments. This reluctance has been labelled constitutional conservatism. The two most important examples of constitutional conventions in the Norwegian political system are parliamentarism and the declining power of the King.
Spain.
Much of Spain's political framework is codified in the Spanish Constitution of 1978, which formalizes the relationship between an independent constitutional monarchy, the government, and the legislature. However, the constitution invests the monarch as the "arbitrator and moderator of the institutions" of government.
Switzerland.
The following constitutional conventions are part of the political culture of Switzerland. They hold true at the federal level and mostly so at the cantonal and communal level. Mostly, they aim to reconcile the democratic principle of majority rule with the need to achieve consensus in a nation that is much more heterogeneous in many respects than other nation-states.
United Kingdom.
While the United Kingdom does not have a written constitution that is a single document, the collection of legal instruments that have developed into a body of law known as constitutional law has existed for hundreds of years.
As part of this uncodified British constitution, constitutional conventions play a key role. They are rules that are observed by the various constituted parts though they are not written in any document having legal authority; there are often underlying enforcing principles that are themselves not formal and codified. Nonetheless it is very unlikely that there would be a departure of such conventions without good reason, even if an underlying enforcing principle has been overtaken by history, as these conventions also acquire the force of custom. Examples include: