The intellectual foundations of modern constitutional democracy were laid during the European Enlightenment, an 18th-century philosophic movement marked by its rejection of traditional social, religious, and political ideas and its emphasis on rationalism. Two of its most influentual thinkers were English political philosopher John Locke and French jurist and political philosopher Montesquieu.
In 1690 Locke published his seminal Two Treatises of Government. His assertion that all legitimate government rests upon "the consent of the governed" profoundly altered discussions of political theory and promoted the development of democratic institutions.
With his assertion of natural law, Locke rebutted the claim that government, specifically monarchy, was an aspect of a divinely ordained chain of being. Natural law is identical with the law of God, Locke argued, and guarantees to all men basic rights, including the right to life, to certain liberties, and to own property and keep the fruits of one's labor. To secure these rights, Locke argued, men in civil society enter into a contract with their government. The citizen is bound to obey the law, while the government has the right to make laws and to defend the commonwealth from foreign injury -- all for the public good. Locke asserted that when any government becomes lawless and arbitrary, the citizen has the right to overthrow the regime and institute a new government.
Locke's theory of natural law inspired a generation of Enlightenment philosophers in Europe and the New World -- from Jean Jacques Rousseau in France to David Hume in Scotland, Immanuel Kant in Germany, and Thomas Jefferson and Benjamin Franklin in what became the United States. But his foremost successor was probably Montesquieu who, like Locke, believed in repubican government based on the consent of the governed, but not in democracy founded on majority rule. In The Spirit of Laws, published in 1748, Montesquieu advocated separating and balancing powers between the executive, legislative, and judicial branches of government as a means of guaranteeing the freedom of the individual. This doctrine also helped to form the philosophical basis for the U.S. Constitution, with its division of power among the presidency, the Congress, and the judiciary.
-- Jeanne S. Holden