Reserve power 

Typically these powers are:

1. to appoint a Prime Minister;
2. to dismiss a Prime Minister;
3. to refuse to dissolve Parliament;
4. to force a dissolution of Parliament;
5. to refuse or delay the Royal Assent to legislation. [1]

There are usually strict conventions concerning when these powers may be used, and these conventions are enforced by public pressure. Using these powers in contravention of tradition would generally provoke a constitutional crisis.

Some political scientists believe that reserve powers are a good thing in that they allow for a government to handle an unforeseen crisis and that they use of convention to limit the use of reserve powers allows for more gradual and subtle constitutional evolution than is possible through formal amendment of a written constitution. Others believe that reserve powers are vestigial and potentially dangerous parts of a constitution.

Reserve powers often originate in situation in which the head of state begins with vast discretionary powers which over time become more difficult to execute in practice without provoking a constitutional crisis. As a society becomes more democratic, conventions and limitations on the power of the head of state become increasingly established and constitutional evolution occurs by establishing conventions rather than by formal amendment of the constitution. As a result, reserve powers often exist in the context of constitutional monarchies.

Reserve powers can also be written into a constitution as was the case of Germany under the Weimar Republic and the French Fifth Republic. The abuse of reserve powers has often been cited as an important factor which allowed for the rise of Nazism in Germany in the 1920s.

Within the Commonwealth of Nations until the 1920s, most reserve powers were exercised by a governor-general, on the advice of the British government, normally in the form of written instructions issued to him when he took office. For example, the first Governor-General of the Irish Free State, Tim Healy was instructed by the British Dominions Office in 1922 to withhold the Royal Assent on any Bill passed by the two houses of Oireachtas Éireann (the Irish parliament) that attempted to change or abolish the Oath of Allegiance. However no such Bill was introduced during Healy's period in office (1922-28). By the time the Oath was abolished, some years later, the Irish Governor-General, like all Commonwealth governors-general, was formally advised exclusively by the Irish government, following a Commonwealth conference decision in 1927 to remove the role of formally advising a governor-general from the British government and give it instead to the national government in each dominion.

In most states, the head of state's ability to do any or all of the above is explicitly defined and regulated by the text of the constitution. In particularly, the Basic Law of Germany strictly limits the reserve powers available to the President to prevent the situation in which the executive could effective rule without legislative approval, which was the case in the Weimar Republic.

Notes

[1] To withhold the Royal Assent amounts to a veto of a Bill. To reserve the Royal Assent in effect amounts to a decision neither to grant or refuse a dissolution, but to delay taking a decision for an undetermined period of time.

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