A constitution, a document that establishes a framework for a government, is frequently describes as "rigid" if changing the provisions of the constitution is unusually difficult. This type of constitution is distinguished from a flexible constitution, in which the governing rules can be changed as easily as an ordinary law can be created. The structures of a rigid constitution therefore often create two levels of laws, with one being superior to the other because the higher level of law cannot be changed with the same ease as ordinary laws, and the higher level governs how ordinary laws are made. The United States' Constitution is a rigid one, while the United Kingdom's is considered flexible.

Examples in Britain and the U.S.

Historically, Great Britain's constitution is an example of a flexible constitution because the country can alter it through a simple act of Parliament. The United States' Constitution, however, is rigid because the country can only amend the document through an extensive process involving both Congress and ratification by a two-thirds majority of the individual states. In addition, the U.S. Constitution is deemed the "law of the land," and can be used by the Supreme Court to overrule provisions passed by Congress. If the Supreme Court determines a law violates the Constitution -- and is thus called unconstitutional -- that law ceases to exist.

Rigidity vs. Flexibility

Constitutional scholar James Bryce argues that rigid constitutions tend to be less stable than flexible documents. Rigid constitutions are typically a single document drafted in a short period of time, while flexible constitutions are a compiled series of laws generated over centuries or even millennia. According to Bryce, a rigid constitution is often less stable than a flexible one because flexible laws with deep history are more respected by their citizens, and come from more conservative nations.