Among the most important factors affecting the success and survival of federal states is their capacity to respond to change and to the challenges associated with it.

The constitutional arrangements within a federal system for dividing power, resolving disputes, safeguarding rights, and providing for reform and renewal are crucial in responding to these challenges.

To many readers, the term “constitutional architecture” may sound odd, but it points to an important, if often overlooked, feature of constitutionalism in federations. In every federal system, political arrangements at the national level are structured by a federal constitution, and in some federal systems, the federal constitution prescribes the political institutions and processes for the country’s constituent units as well, thus dictating the constitutional architecture for the entire federal system.¹ India, Belgium, and Nigeria, for example, have altogether dispensed with sub-national constitutions external to the federal constitution.² And the South African Constitution both serves as a national constitution and provides a model provincial constitution that operates unless a province adopts its own constitution. But in most federal systems the federal constitution is an “incomplete” framework document, in that it does not prescribe all constitutional processes and arrangements. Rather, it leaves “space” to be filled by the constitutions of its sub-national units. The scope of this sub-national constitutional space varies from one federal system to another – typically, the less detail that the federal constitution provides or that it requires of sub-national constitutions, the greater the sub-national constitutional space. Federal constitutions also set parameters that constrain the choices available to those drafting sub-national constitutions.³ Nonetheless, this system of dual constitutionalism furnishes an opportunity for constituent units to define their own goals and establish their own governmental institutions and processes.

Our emphasis on self-rule should not obscure the fact that sub-national constitutions also form part of the overall constitutional framework for the federation. As Daniel Elazar has observed, sub-national constitutions are “part and parcel of the total constitutional structure of federal systems and play a vital role in giving the system direction.”⁴ For present purposes, this means that dual constitutionalism can promote constitutional adaptation to changing circumstances. Constituent units may use the constitutional space available to them to initiate reforms that respond to the problems they confront, and these experiments may have consequences beyond their own borders. A successful experiment in one constituent unit may promote emulation by other constituent units that confront the same problems: what has often been referred to as horizontal federalism. In addition, successful experiments in the constituent units may induce the federal government to adopt the same reforms at the national level, a form of vertical federalism in which the pattern of influence is bottom-up rather than top-down. Thus, to understand fully constitutional evolution and development in federal and quasi-federal systems, one must constantly be mindful of the interplay of federal and sub-national constitutions.