Montesquieu's Separation of Powers: From Theory to Constitutional Practice

The doctrine of the separation of powers is one of the most influential ideas in the history of modern political thought, and its development in the work of Montesquieu is one of the great examples of a theoretical idea transforming the practice of government. While The Separation of Powers surveys the doctrine as a whole, this article focuses on the biographical and textual context in which Montesquieu developed the doctrine, the specific arguments of Book XI of The Spirit of the Laws, and the ways in which the American founders adapted his theory to the new republican context.

The Biographical Context

Montesquieu developed the doctrine of the separation of powers in the years following his return to France from his extended tour of Europe (1728–1731). The tour, and especially his time in England, was decisive for his political thought. England, in his view, was the only country in Europe in which political liberty was effectively protected, and he was determined to understand the institutional arrangements that made this possible. He read the English legal tradition, observed the proceedings of Parliament, and conversed with English lawyers, politicians, and country gentlemen.

The intellectual context was also important. Montesquieu was deeply read in the Roman law tradition, and he was particularly influenced by the Roman theory of the mixed constitution — the theory, going back to Polybius, that the best form of government was one in which the monarchical, aristocratic, and democratic elements were balanced against each other. He was also influenced by the French political theorists of the seventeenth century, including Jean Bodin, who had developed the theory of sovereignty, and the various writers of the French monarchomach tradition, who had developed the theory of the right of resistance to tyranny. The doctrine of the separation of powers, as Montesquieu developed it, was a synthesis of these various traditions, adapted to the conditions of modern commercial society.

The Arguments of Book XI

The doctrine of the separation of powers is developed in Book XI of The Spirit of the Laws (1748), the most famous section of Montesquieu’s masterwork. Book XI is a study of the English constitution, which Montesquieu took as a model of the proper organization of political power.

The central argument of Book XI is that political liberty depends on the proper arrangement of the laws and institutions of a country, and that the proper arrangement is one in which no single person or group can exercise arbitrary power over the others. Montesquieu distinguished among three kinds of political power: the legislative power (the power to make laws), the executive power (the power to execute the laws and to manage the day-to-day affairs of the state), and the judicial power (the power to judge disputes between individuals). He argued that each of these powers should be exercised by a distinct body, and that the concentration of any two or more of them in the same person or body would be a threat to political liberty.

The most famous passage of Book XI is the statement of the principle: “There can be no liberty where the legislative and executive powers are united in the same person, or in the same body of magistrates; or, if the power of judging be not separated from the legislative and executive powers.” The statement captures the essence of the doctrine: liberty requires that the powers of government be distributed among distinct bodies, each of which can check the others.

The American Adaptation

The American founders were deeply read in Montesquieu, and the American Constitution of 1787 was directly influenced by the doctrine of Book XI. The framers of the Constitution adapted Montesquieu’s arguments in several important ways. They accepted the basic tripartite structure of the doctrine — legislative, executive, and judicial — and they designed the new national government around this structure. They added, however, a more elaborate system of checks and balances than Montesquieu had proposed, and they made the judiciary independent of the other two branches in a way that Montesquieu’s account of the English constitution did not anticipate.

James Madison, in the Federalist Papers, developed Montesquieu’s arguments. Madison argued that the separation of powers was necessary to control the “violence of faction” — the tendency of human beings to form groups with interests opposed to the rights of other groups or to the common good. The extended republic designed by the Constitution, with its many factions and interests, would, Madison argued, make the separation of powers an even more effective mechanism for the protection of liberty than it had been in the small republics of Montesquieu’s theory.

The Contemporary Significance

The contemporary practice of constitutional government in many parts of the world is a direct descendant of the Montesquieuian principles. The French constitutional tradition, the European constitutional courts, the Latin American constitutional systems, the various African and Asian constitutional systems developed in the twentieth century — all are, descendants of the doctrine of the separation of powers as developed by Montesquieu in Book XI of The Spirit of the Laws.

The contemporary engagement with the doctrine is, however, also a critical engagement. The contemporary constitutional democracies have, moved beyond the strict separation of powers that Montesquieu proposed. The modern administrative state, with its elaborate system of regulatory agencies, has blurred the boundaries between the legislative, executive, and judicial powers. The contemporary debate about the proper limits of judicial review, the proper role of regulatory agencies, and the proper relationship between the branches of government is, a continuation of the debate that Montesquieu began.

The Biographical Context

The Arguments of Book XI

The American Adaptation

The Contemporary Significance

Further Reading