The theoretical foundations of modern constitutionalism were laid down in the great works on the social contract, especially those of the English philosophers Thomas Hobbes and John Locke in the 17th century and the French philosopher Jean-Jacques Rousseau in the 18th.

As a result of the Reformation the basis of divinely sanctioned contractual relations was broken up. The Holy Roman Empire was torn apart by the wars of the Reformation. Henry VIII made the Church of England independent of Rome. In these circumstances, it became necessary to search for a new basis of order and stability, loyalty and obedience. In their search, political theorists—and especially the Protestants among them—turned to the old biblical concept of a covenant or contract, such as the one between God and Abraham and the Israelites of the Old Testament.

In a sense, the secular theorists of the social contract almost reversed the process of choice. Instead of God choosing his people, a people through its representatives was now looked upon as choosing its governors, or its mode of governance, under God, by means of a social contract or constitution. According to modern theories of the social contract, the political unit is nevertheless established as in the biblical model by means of a promise or promises.

Thomas Hobbes’s state, or “Leviathan,” comes into being when its individual members renounce their powers to execute the laws of nature, each for himself, and promise to turn these powers over to the sovereign—which is created as a result of this act—and to obey thenceforth the laws made by this sovereign. These laws enjoy authority because individual members of society are in effect their co-authors. According to Locke, individuals promise to agree to accept the judgments of a common judge (the legislature) when they accede to the compact that establishes civil society. After this (in one interpretation of Locke’s Second Treatise on Civil Government), another set of promises is made—between the members of the civil society, on the one hand, and the government, on the other. The government promises to execute its trust faithfully, leaving to the people the right to rebel in case the government breaks the terms of the contract, or, in other words, violates the constitution. Subsequent generations accept the terms of the compact by accepting the inheritance of private property that is created and protected by the compact. Anyone who rejects the constitution must leave the territory of the political unit and go in vacuis locis, or “empty places”—America, in Locke’s time. In his Letters on Toleration, Locke characteristically excluded atheists from religious toleration because they could be expected either not to take the original contractual oath or not to be bound by the divine sanctions invoked for its violation. For Rousseau, too, the willingness to subject oneself to the “general will” to which only the popular sovereign can give expression is the essential ingredient of the social contract. In taking this position, Rousseau may have been influenced by the experience of his native Geneva. The Swiss Confederation is still referred to officially, in German, as an Eidgenossenschaft, a term best translated as “fellowship of the oath.”