(1) Formal Growth:
The fist way in which forces work is that they create circumstances necessitating change through a process of formal amendment, judicial interpretation and the establishment of conventions.
Changes in the constitution may also be made by statutory elaboration, treaty-agreements and executive ordinance. Every constitution generally provides for a method of amendment, instance.
Article V of the U.S. Constitution provides that amendment of the constitution may be made, if the proposal is passed by a two-thirds majority in each. House of Congress, and is thereafter accepted by the legislatures of the States. Similarly, the Constitution of India lays down in Article 368 the various procedures of amendment.
(2) Informal Growth :
Informal changes are effected by various forces. For instance, it has been found that in recent times the central governments in most of the Federations have come to acquire more and more power.
This growth in centralisation is not, in most cases, the result of formal constitutional amendments; it is rather due to forces such as war. Economic crisis, planning, the growth of social services, etc.
To quote Where, “It was federal governments come near to being unitary governments, not by any alteration in words of the constitution but by the bringing into the ambit of the defence power of many matters of great importance which in peace time would clearly lie within the authority of the States.”
Thus the scheme of division of powers, which is the essence of federalism, is distributed by various factors. It brings vital change in the spirit of the constitution and it takes place informally. Informal changes are also effected by the operation of the party system, the electoral system and conventions.
As Wheare again writes, “The moral authority which a constitution claims and can claim is related very closely, therefore, to the structure of the community for which it purports to provide the foundations of law and order. It must embody forms of governments in which a community believes; it must be adapted to their capacity for government.