Charles de Secondat, Baron de Montesquieu was a leading legal and social philosopher of the French Enlightenment. He is best known for the theory of separation of powers, which he advanced as a safeguard against arbitrary rule. Montesquieu’s ideas deeply impressed the American Founders, particularly James Madison, and the U.S. Constitution owes much to Montesquieu’s analysis of the nature of good government.

Montesquieu inherited great wealth and a magistracy in the parlement of Bordeaux—a regional law court, rather than a legislative body. In the 18th century, the parlements of France represented one of the few independent authorities in the French state, and Montesquieu learned much about government from firsthand experience. Often the parlements feuded with the monarchy; Montesquieu was to witness arbitrary power in the person of Louis XIV, whom he later lampooned in his writings. The parlements regularly demanded that religious prisoners be set free and that no taxes be approved without their assent; the struggles over these issues are often reflected in Montesquieu’s political writings.

In 1721, Montesquieu published the Persian Letters, a fictional compilation of letters exchanged by and about two Persians traveling throughout Europe. The visitors ridicule not only the vanity and folly of Europe, but also its despotic governments, oppressive laws, religious intolerance, and hypocrisy. They also ridiculed the sale of offices, monetary devaluation, and even the idea that war could enrich a country.

What elevates the Persian Letters above mere satire is the way in which the letters’ fictional authors failed to recognize their own illiberality; one of them, Usbek, both owns eunuchs and keeps a harem, over which he extends a cruel and despotic rule. The work therefore makes the point that, although the principles of liberty may be easy to understand when applied to someone else, it is far more difficult to restrain one’s own impulses toward tyranny. The Persian Letters was published anonymously to avoid imprisonment for its author, yet his identity was sufficiently well known that, with only a handful of minor works to his name, Montesquieu was elected to the Académie Française.

Montesquieu’s greatest work, The Spirit of the Laws, was far more ambitious. Published in 1748, it aimed to explain in purely natural terms the various systems of government encountered throughout the world, how they grew and developed, and how they declined and ultimately collapsed. The result is a digressive and omnivorous work, containing observations about climate, agriculture, technology, history, economics, and philosophy. Some of its ideas, particularly those about climate and geography, are now merely of historical interest and have little value except as curiosities. Others, however, continue to exert a profound influence on modern politics.

One notion that runs throughout The Spirit of the Laws is the idea that we must judge all laws by their actual effects, not by their intentions or by the wickedness of the crime they are meant to suppress. In this regard, Montesquieu can be seen as a predecessor of libertarian consequentialism. In a particularly insightful passage, he wrote, “Among us, three crimes stand out: magic, heresy, and the crime against nature. We may say of the first, that it does not exist; of the second, that it is subject to infinite distinctions and interpretations; and of the third, that it is very often secretive. Yet all three are punished by burning at the stake.” Montesquieu argued that laws of this type were bad because they augmented arbitrary power and that the evil they did far outweighed any possible good that they might achieve. The vagueness of a law, Montesquieu argued, leads directly to tyranny.

Montesquieu contended that the legitimacy of a law required not only its predictability, but strict limits on the powers of government. Anticipating the words of Lord Acton, he wrote, “Eternal experience shows that all men who have power come to abuse it, and this they will do to the limits of their power.” The great question of political thought now becomes how to prevent the abuse of power, and Montesquieu supplied an answer that would have far-ranging consequences in the modern world.

The most important contribution of The Spirit of the Laws was the claim that government power can be effectively limited by dividing it into a legislative power, whose function was to write the laws, an executive power, which enforces the laws, and a judicial power, empowered to interpret the laws and settle disputes arising under them.

Montesquieu proposed that each of these three powers should be assigned to a separate agency or individual within the state and that these powers should be constituted in such a way that they will act as restraints on one another. “So that none can abuse power, we must arrange, by the disposition of things, that power shall check power,” Montesquieu wrote.

The aims of his system were personal security and personal liberty, which Montesquieu regarded as nearly the same thing: “The government must be such that one citizen will not live in fear of another,” he wrote. Montesquieu cited only two significant examples of governments that agreed with his theories: Britain and the Roman Republic. He argued that Rome lost its liberty when it abandoned the separation of powers, but that Britain retained a significant share of its own liberty owing to the separation of the King, the Parliament, and the court system.

Montesquieu had relatively little impact in France; the political theories of Jean-Jacques Rousseau were far more evident in the era of the French Revolution. Yet he achieved a remarkable posthumous success in the United States. As James Madison wrote in Federalist no. 47, “the oracle who is always consulted and cited on this subject is the celebrated Montesquieu.” The Spirit of the Laws comported well with the colonists’ understanding of government both because they were accustomed to the British system, which Montesquieu praised, and because they had come through experience to share Montesquieu’s suspicion of arbitrary power. Montesquieu offered powerful arguments in favor of a three-branch system containing checks and balances on the power of each branch of government, and Madison noted how both the state constitutions and the proposed federal one were in keeping with Montesquieu’s design.

A vigorous debate exists today among libertarians regarding Montesquieu’s ideas on state power. Some argue that the separation of powers and checks and balances derived from Montesquieu’s thought can indeed form the basis of a limited government, and that, aided by further insights about the nature of government, we can erect effective checks on its power that will prevent it from violating any individual rights. Those who share this opinion tend to describe themselves as minarchists, and they tend to work within existing systems of law with a view toward limiting, but not eliminating the state.

Others, however, observe that no government has ever fully respected individual liberty and that all limitations on government power have tended to break down over time. They tend to view Montesquieu’s system and others like it as well-intentioned failures, and they note that theories of limited government have prevented neither the tyrannical regimes of the 20th century nor the advance of socialism within Britain and the United States. Thinkers of this persuasion tend to reject Montesquieu’s theories of government and instead favor various systems of libertarian anarchy.

Further Readings

Hamilton, Alexander, James Madison, and John Jay. The Federalist. Maria Hong, ed. New York: Pocket Books, 2004.

Lacouture, Jean. Montesquieu: les vendanges de la liberté. Paris: Seuil, 2003.

Lutz, Donald S. “The Relative Influence of European Writers on Late Eighteenth-Century American Political Thought.” American Political Science Review 78 no. 1 (March 1984): 189–197.

Montesquieu, Charles de Secondat, baron de. The Persian Letters. George R. Healy, trans. Indianapolis, IN: Hackett, 1999.

———. The Spirit of the Laws. Anne M. Cohler et al., eds. and trans. New York: Cambridge University Press, 1989.

Shackleton, Robert. Essays on Montesquieu and on the Enlightenment. David Gilson and Martin Smith, eds. Oxford: Voltaire Foundation at the Taylor Institution, 1988.