The Separation of Powers: Foundation of Constitutional Government

The doctrine of the separation of powers is the most successful piece of constitutional engineering in the history of modern government. It is also, like most successful pieces of engineering, a doctrine that almost everyone praises in the abstract and that most people in office would happily circumvent in the particular. Montesquieu, who gave the doctrine its most influential form in Book XI of The Spirit of the Laws (1748), was almost certainly wrong about the English constitution he claimed to be describing. The Americans who adopted the doctrine in 1787 knew this and adapted it anyway. The result is the Constitution of the United States, which is, two hundred and thirty-eight years later, still the working framework of the oldest constitutional democracy in the world. The doctrine has had a more complicated history in Europe, and a complicated afterlife in the academic literature, but the basic idea — that political power should be divided among different branches of government, each of which would check the others — has proved one of the most durable inventions of the Enlightenment.

The interesting historical question is why the doctrine worked in America, more or less as designed, when it has worked less well in other places. The answer has something to do with the specific circumstances of the American founding, something to do with the qualities of the American political class, and something to do with the gradual working out of constitutional convention through the long nineteenth century. The doctrine is not a self-executing piece of constitutional machinery; it works only when the political culture in which it is embedded is willing to take it seriously.

The background: a very old idea

The idea of dividing political power among different bodies is not new with the Enlightenment. The ancient Roman Republic had a complex system of checks and balances among the consuls, the senate, and the popular assemblies. The medieval English constitution had developed a system of mutual checks between the king, the lords, and the commons. The mixed-government tradition, which held that the best form of government was one that combined the principles of monarchy, aristocracy, and democracy, was an important feature of political thought from Aristotle through the Renaissance. Polybius was the most sophisticated ancient theorist; Cicero developed the tradition in the Roman context; the medieval theorists of the mixed constitution applied it to the English case.

What was new in the Enlightenment was the systematic theoretical formulation of the doctrine, and the attempt to apply it in a new and more rigorous way. The contribution of Montesquieu was to articulate the principle in a way that was both theoretically sophisticated and practically applicable, and to provide a model — the English constitution — that demonstrated how the principle could be embodied in a real political system.

Montesquieu’s theory

Montesquieu (1689–1755) developed the most influential version of the separation of powers doctrine in Book XI of The Spirit of the Laws (1748). Drawing on his reading of the English constitution, Montesquieu distinguished among three kinds of political power: the legislative power, the executive power, and the judicial power. 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.

Montesquieu’s most famous statement of the principle is: “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 sentence is the founding text of the modern doctrine, and it has been quoted in almost every work on constitutional theory since 1748.

The argument was grounded in a more general theory of political liberty. Montesquieu held that political liberty depended on the proper arrangement of the laws and institutions of a country, and that the proper arrangement was one in which no single person or group could exercise arbitrary power over the others. The separation of powers was, in his view, the most effective institutional mechanism for achieving this arrangement.

The English constitution as Montesquieu described it was not, however, a clean separation of three distinct powers. The king, the House of Lords, and the House of Commons shared legislative, executive, and judicial functions in a complex system of overlapping jurisdictions. The Cabinet, which had not yet developed into its modern form, was a hybrid body; the House of Lords functioned as the highest court of appeal; the king retained significant legislative and judicial functions. Montesquieu’s account was a simplification, and his English correspondents told him so. He replied, in effect, that the simplification was the point: he was describing not the English constitution as it actually was, but the constitution as it ought to be understood. The reply was either brilliant or evasive, depending on one’s taste. The Americans, who read The Spirit of the Laws carefully, treated it as a description of the constitutional ideal rather than a description of the English reality, and they were right to do so.

The features of the English constitution that Montesquieu admired were the independence of the judiciary (which was exercised by juries in criminal cases and by judges who held their offices during good behavior), the separation of the legislative power between the House of Lords and the House of Commons with the further check provided by the royal power to consent to or to reject legislation, and the separation of the executive power from the legislative. This system of mutual checks, Montesquieu argued, was the foundation of English political liberty, and it was the model that other countries should follow.

The American application

The doctrine of the separation of powers was given its most successful practical application in the Constitution of the United States (1787). The framers of the Constitution drew directly on Montesquieu’s arguments, and the American system of government was explicitly designed to embody the principles of the separation of powers.

The Constitutional Convention, which met in Philadelphia in 1787, was deeply concerned with the problem of how to prevent the concentration of political power. The Articles of Confederation, which had governed the United States from 1781 to 1789, had created a national government that was too weak to govern effectively. The problem for the framers of the Constitution was to create a government that would be strong enough to govern, but not so strong that it would threaten the liberty of the citizens. The solution that the framers developed was a system of government with three branches — legislative, executive, and judicial — each of which was given its own powers, and each of which was subject to the checks of the others.

The Congress, consisting of the Senate and the House of Representatives, exercised the legislative power. The President, elected for a fixed term, exercised the executive power. The Supreme Court, appointed by the President with the consent of the Senate, exercised the judicial power. The system was not a clean separation of three distinct powers — Montesquieu’s three-fold distinction was, in fact, a simplification — but a system of overlapping jurisdictions and mutual checks. The President could veto legislation, but the veto could be overridden by a two-thirds vote of both houses. The Senate could refuse to confirm presidential appointments and treaties. The Supreme Court could declare laws unconstitutional, and the President could nominate justices only with the consent of the Senate. The framers knew that the system would not work perfectly, and they designed it to work tolerably well under conditions of ordinary political conflict.

The most systematic theoretical defence of the American system was provided by the Federalist Papers, written by Alexander Hamilton, James Madison, and John Jay in 1787–1788 to support the ratification of the Constitution. Madison’s contribution, in Federalist No. 10, drew on Montesquieu’s arguments and developed them. 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 system of checks and balances established by the Constitution was, in Madison’s view, the most effective institutional mechanism for protecting the rights of minorities against the tyranny of the majority.

The Bill of Rights, added to the Constitution in 1791, was an important supplement to the system of checks and balances. The first ten amendments enumerated a series of fundamental rights — freedom of speech, freedom of the press, freedom of religion, the right to bear arms, the right to a fair trial, the right to be secure against unreasonable searches and seizures — that were designed to protect the citizens against the arbitrary power of the national government. The Bill of Rights was based on the natural-rights tradition of the Enlightenment, and it was an important contribution to the development of the modern theory of constitutional rights.

The French and European variations

The American system of the separation of powers was widely imitated in the constitutional systems of other countries, but the principle was applied in different ways. The French Revolution produced a series of constitutions that attempted to apply the principles of the separation of powers, but the French system developed in a different direction from the American. The French constitutions of 1791, 1793, and 1795 all attempted to divide political power among different bodies, but the French tradition was more concerned with the supremacy of the legislature than with the balance of powers among the branches. The French constitutional tradition thus developed in a more parliamentary direction, with the legislature occupying the central place in the constitutional order. The French tradition has, accordingly, been more comfortable with the idea of a strong parliament and a relatively weak executive; the American tradition has been more comfortable with the idea of a strong executive and a strong legislature in mutual tension.

The European constitutional tradition developed in two main directions. The British tradition, with its system of parliamentary sovereignty, allowed for the predominance of the legislature, while maintaining the independence of the judiciary and the rule of law. The Continental tradition, influenced by the American and French examples, developed a system of constitutional review, in which a special constitutional court would assess the constitutionality of legislation. The Austrian Constitutional Court (1920), the German Federal Constitutional Court (1951), and the various other European constitutional courts that have been established since 1945 are all products of this tradition.

The contemporary European constitutional tradition is a complex mixture of these various influences. The European Convention on Human Rights, the European Court of Human Rights, and the constitutional courts of the European nation-states all operate in a tradition that traces its lineage back to the Enlightenment theory of the separation of powers.

The three critiques

The doctrine of the separation of powers has been criticized from several directions.

The efficiency critique is that the separation of powers is inefficient, in that it makes it more difficult for the government to take decisive action. The American system of checks and balances, in this view, leads to gridlock and inaction, and it prevents the government from addressing the urgent problems of contemporary society. This critique has been voiced in different forms throughout American history. The Progressive movement of the early twentieth century, the New Deal of the 1930s, and various reform movements of the late twentieth century all criticized the separation of powers as an obstacle to effective government. The contemporary debate about gridlock in American politics is a continuation of this critique.

The democratic critique is that the separation of powers is undemocratic, in that it gives too much power to the judiciary and to other non-elected branches. In a true democracy, the argument goes, the people should govern themselves through their elected representatives, and the unelected judiciary should not have the power to overrule the elected legislature. This critique has been voiced especially in the contemporary debate about judicial review. Critics of judicial review have argued that the practice gives too much power to unelected judges and that it undermines the democratic legitimacy of the constitutional order. The argument has a real force, but it is also vulnerable to the obvious reply: in a constitutional democracy, the protection of individual rights and the limitation of governmental power are exactly the jobs that the judiciary is supposed to do.

The functionalist critique is that the separation of powers is based on a misunderstanding of how modern government actually works. In contemporary government, the argument goes, the three branches of government are not really separated; they are interconnected in complex ways, and the rigid separation of powers is an obstacle to the proper functioning of the constitutional order. The executive is involved in legislation through the budget process and the veto; the legislature is involved in administration through oversight and the confirmation of executive officials; the judiciary is involved in both through the interpretation of statutes. The result, in the contemporary account, is a system of “separated institutions sharing power,” to use Richard Neustadt’s phrase, rather than a clean separation of three distinct branches.

The contemporary significance

Despite the various critiques, the separation of powers remains one of the basic principles of modern constitutional government. The principle has been applied in different ways in different countries, and the contemporary practice of constitutional government is a continuation of the Enlightenment project of limited government and the rule of law.

The most important contemporary development in the theory of the separation of powers is the rise of constitutional review. The practice of judicial review, in which courts assess the constitutionality of legislation, has become a basic feature of constitutional government in many countries, and it represents an important extension of the Enlightenment principle that political power should be subject to the rule of law. The practice is contested, especially in the United Kingdom, where it has been traditionally rejected, and in France, where it has been accepted only in modified form. The practice is also evolving: the contemporary constitutional court is not just a negative check on the legislature but a positive participant in the development of constitutional law, and the proper relationship between constitutional review and democratic self-government is one of the central questions of contemporary constitutional theory. The debate is not closed, and it is not going to be closed, because the question is one of the permanent questions of constitutional government.