Modern nation-states enact constitutions to bring society from its natural state of chaos to organization based on the rule of law. Unlike the war of all against all described by the English philosopher Thomas Hobbes (1588-1679), John Locke’s (1632-1704) view of the state of nature recognized that humans have organized in family and cultural units throughout history. Though unnecessary for protection from outsiders, society could benefit from a social contract. Participants must agree to create structure (a legislature to make decisions), to designate an impartial judge, and to establish enforcement powers (an executive branch) in order to sustain a peaceful society. These entities, according to Locke, can only be created through the efforts of the members of a society to contract for continued institutional support.
The social contract is often embodied by a constitution, a set of principles by which a group of people agrees to govern and be governed. In order to operate as a constitution, these rules need not take the form of a written document. The social contract metaphor is limited in several ways, including, in most circumstances, the lack of third-party enforcement. It is more important that constitutional law represents the conventions accepted in a society, and that societal order is coordinated around these conventions. A "dualist" understanding views constitutions as frameworks within which other politics and institutions operate. They establish second-order rules that must be followed when making more specific laws.
By constraining rulers, constitutions aim to protect citizens’ rights. When a constitution stipulates judicial review, citizens can petition courts to invalidate laws that violate constitutional principles. Although, as with the unwritten British constitution, not all provisions are judicially enforceable, they may nonetheless serve as focal points for legal interpretation and political debate, as well as indicators of which government interventions will be accepted by citizens.
A constitution serves, in some sense, to codify existing social relations. Constitutional design, therefore, is constrained by internal and external power dynamics. Resulting agreements reflect these relationships rather than pure legal ideals. As a result, underrepresented groups continue to be excluded, unless they gain influence by extra constitutional means.
Russell Hardin (1999) sees constitutions more as models of mutual advantage than as binding contracts. It is usually in the best interest of all parties to uphold the rules that maintain order within their society. There are relatively few occasions when it would be more difficult to follow existing rules than to renegotiate the terms of a constitution.
Those rare circumstances on which recoordination is less costly for society are constitutional moments (Ackerman 1991). Changes in power alignments, in relation to internal politics or external influence, may necessitate a change in the substance of a constitution. These moments may involve major amendment to an existing constitution, as in the post-Civil War United States, or they may require a complete overhaul of the constitution, as in South Africa following the inclusion of the black population as full citizens in the 1990s. At these times, questions of legitimacy arise because the constitutional authors have not been elected by a process representing the new social contract, and may not represent the people who will be bound by the new document. If a new constitution is to remain a stable set of rules for the polity, it must represent a credible commitment by citizens and leaders who will not have an incentive to override or renegotiate it, or resort to violence. Such constitutional moments may arise in the context of postwar reconstruction, independence movements, domestic upheaval, or union of existing polities. In each situation, citizens encounter distributional gains and losses reflecting societal change.
