Constitutional monarchy is a form of government in which a monarch is legally restricted within the boundaries of a constitution. This form of government differs from absolute monarchy, in which the monarch has absolute political power over the state and is not effectively restricted by constitutional constraints. Constitutional monarchies are sometimes referred to as limited monarchies or crowned republics.[a] A constitutional monarchy is a parliamentary monarchy, however there are also parliamentary absolute monarchies such as Oman.A constitutional monarchy may refer to a system in which the monarch acts as a non-party political head of state under the constitution, whether written or unwritten. While the monarch may hold formal reserve powers and government may officially take place in the monarch's name, they do not set public policy or choose political leaders. Political scientist Vernon Bogdanor, paraphrasing Thomas Macaulay, has defined a constitutional monarch as "a sovereign who reigns but does not rule." In addition to acting as a visible symbol of national unity, a constitutional monarch may hold formal powers such as dissolving parliament or giving Royal Assent to legislation. However, the exercise of such powers is generally a formality rather than an opportunity for the sovereign to enact personal political preference. In The English Constitution, British political theorist Walter Bagehot identified three main political rights which a constitutional monarch could freely exercise: the right to be consulted, the right to advise, and the right to warn. Some constitutional monarchs, however, retain significant power and influence and play an important political role.The United Kingdom and fifteen of its former colonies are constitutional monarchies with a Westminster system of government. Three states—Malaysia, Cambodia, and the Holy See—employ true elective monarchies, where the ruler is periodically selected by a small, aristocratic electoral college.The most recent[update] country to transition from an absolute to a constitutional monarchy was Bhutan, in 2007-08.