Hereditary Monarchy
Form of monarchy in which "all the monarchs come from the same family, and the crown is passed down from one generation to the next" (Economic Expert). The crown is usually given to the oldest son of the sovereign. Sons always have precedence over daughters, but daughters over the sons of the sovereign´s brothers (Aspects of Britain 18). Since the Act of Settlement in 1701 only Protestant are eligible to succeed to the throne. This rule can only be changed by all members of the Commonwealth (ibid. 16). The Act of Settlement indicates the control Parliament has over the laws of succession, nevertheless, the hereditary principle was not abandoned (Nenner 10).
Hereditary Monarchy an illusion?
By what right did an English monarch ascend the throne? Not even Henry IV was sure of that: "With what right I got it, God only knows!" (ibid. 1). In theory England has a hereditary monarchy, but in reality there are no regularities. Monarchs in Britain succeeded to the throne by hereditary right or not, they legitimated their way to the throne by conquering or not, they got the right to be king from the parliament or not (ibid.). Beginning with the reign of John in 1199, nearly every succession raised questions about the principle of succession. There had been a lot of violent changes, e.g. Henry VI´s and Edwards IV`s exchanging of places by force or Henry VII`s victory at Bosworth Field. That raises the idea of a de facto kingship: "the right to be king belonged to whoever was king" (ibid. 2).
Sources
Aspects of Britain. The Monarchy. London: HMSO, 1991.
Economic Expert: Hereditary Monarchy. http://www.economicexpert.com/a/Hereditary:monarchy.htm
Nenner, Howard. The Right to be King. The Succession to the Crown of England, 1603-1714. Houndmills: Macmillan Press, 1995.