<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> <P> In most nations, such as the United States, India, and Singapore, constitutional law is based on the text of a document ratified at the time the nation came into being . Other constitutions, notably that of the United Kingdom, rely heavily on unwritten rules known as constitutional conventions; their status within constitutional law varies, and the terms of conventions are in some cases strongly contested . </P>

What is the difference between common law statutory law and constitutional law
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