As distinguished from a unitary State, a federation has the following characteristics:
Supremacy of the Constitution
The supremacy of the constitution lies in the very nature of the federation. A federation is an agreement between two-or more sovereign States to form a new State in which they exercise certain specific powers. This agreement is the constitution. It defines the powers and functions of both the central and provincial or unit governments. It must of necessity be supreme over both, so that none of them may violate its provisions and encroach upon the rights and powers of the other.
The supremacy of the constitution ensures that the two sets of authorities, central and provincial, remain within their allotted sphere of powers. If any one of them does something against the laws of the constitution, its act is illegal and invalid, liecause it is unauthorized by the constitution. If any change in the powers of the national or provincial government is desired, it could only be made by amending the constitution according to the method laid down in the constitution itself. Thus is the supremacy of the constitution ensured. Its supremacy implies three things: (a) it must be a written constitution; (b) it must be a rigid constitution; and (c) sovereignty should lie with the constitution-amending body.
Written Constitution
Constitution must be an inviolable document so that neither the central nor the provincial government may be in doubt about its powers and rights granted by it. In other words, the federal constitution must be written and definite so that there may-be no dispute or doubt about its provisions. Really speaking, sovereign States federate only when they know that their rights and powers are secure under a supreme, definite and written constitution.
Rigid Constitution
Rigidity requires that the constitution can be amended by a definite and difficult process only, which the central government or the unit government cannot set into motion by itself. Thus it will remain supreme and binding on both.
Sovereignty of the amending authority
Sovereignty in a federation lies neither with the federal government nor with the federating governments. It lies only with the constitution-amending body or bodies taken together, as provided by the constitution itself. It means that the legislatures of the central and provincial governments are not sovereign law-making bodies, as they are subordinate to the constitution.