<P> Constitutional law is the body of law which defines the role, powers, and structure of different entities within a state, namely, the executive, the parliament or legislature, and the judiciary; as well as the basic rights of citizens and, in federal countries such as India and Canada, the relationship between the central government and state, provincial, or territorial governments . </P> <P> Not all nation states have codified constitutions, though all such states have a jus commune, or law of the land, that may consist of a variety of imperative and consensual rules . These may include customary law, conventions, statutory law, judge - made law, or international rules and norms . Constitutional law deals with the fundamental principles by which the government exercises its authority . In some instances, these principles grant specific powers to the government, such as the power to tax and spend for the welfare of the population . Other times, constitutional principles act to place limits on what the government can do, such as prohibiting the arrest of an individual without sufficient cause . </P>

The fact that the three branches can only do what is in the constitution is an example of