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, and so on.
Constitutional laws may often be considered second order rulemaking or rules about making rules to exercise power. It governs the relationships between the judiciary, the legislature and the executive with the bodies under its authority. One of the key tasks of constitutions within this context is to indicate hierarchies and relationships of power. For example, in a unitary state, the constitution will vest ultimate authority in one central administration and legislature, and judiciary, though there is often a delegation of power or authority to local or municipal authorities. When a constitution establishes a federal state, it will identify the several levels of government coexisting with exclusive or shared areas of jurisdiction over lawmaking, application and enforcement.
Another main function of constitutions may be to describe the procedure by which parliaments may legislate. For instance, special majorities may be required to alter the constitution. In bicameral legislatures, there may be a process laid out for second or third readings of bills before a new law can enter into force. Alternatively, there may further be requirements for maximum terms that a government can keep power before holding an election.
The doctrine of the rule of law dictates that government must be conducted according to law.
Dicey identified three essential elements of the British Constitution which were indicative of the rule of law:
- Absence of arbitrary power;
- Equality before the law;
- The Constitution is a result of the ordinary law of the land.