A simple definition of power could be the ability both to demand that people do something, and to say how a thing should be done or organised. Authority, however, is where power is granted by consent; and when an individual or committee is said to have authority, the reason that justifies this authority is known as legitimacy. In general, the government has authority because it has legitimacy through: tradition, as Parliament has existed for hundreds of years; charisma, as many people may follow present PM Tony Blair through the strength and attraction of his personality; and democratically through the people, as they vote in elections for the MP or party they wish to form the government. An example of an organisation that has power but not necessarily authority would be the Mafia, which exercise their power by sometimes using violence and force, or money, status, education or sex. In Liberal Democracies such as the UK, power is split into three types: legislative power, which is the power to make laws; executive power, which is the power to implement laws; and judicial power, which is the power to interpret laws.
The two concepts of power and authority can be understood in different ways, for example Steven Luke's three faces of power or Max Weber's three types of authority. The nature, sources, and limitations of political authority and power have been much debated questions since the time of the ancient Greeks. These two sociologist's theories discuss the concepts of power and authority in three stages; Weber distinguished three main modes of claiming legitimacy, and Lukes derived a definition of power in three stages.
Max Weber, whose study took place in the 19th century, decided that authority was split into three types: charismatic authority, traditional authority, and rational - legal authority.