Why separation of powers is about character as well as power

Authored by Charles Lincoln is a lawyer, author, and Ph.D. candidate in international tax law at the University of Groningen. He is the author of Gods, Judges, and Presidents (Bloomsbury Academic, 2026) and The Dialectical Path of Law (2021). His research interests include constitutional theory, comparative law, legal history, and the intellectual foundations of public institutions.

Abstract

Separation of powers is usually introduced as a way of assigning legal authority among legislatures, executives, and courts. Yet many constitutional disputes are really arguments about how those institutions are expected to behave. A court is supposed to reason judicially, an executive to govern and administer, and a legislature to represent disagreement and turn it into law.

Plato's Republic offers a useful way to think about that less formal side of constitutional structure. Its account of a city and a soul whose parts have different work to do, which helps explain why institutional overreach can feel wrong even when no simple boundary line resolves the dispute. Read with Montesquieu, Madison, Polybius, and modern constitutional practice, Plato suggests that the separation of powers is partly about preserving different kinds of public judgment.

The article aims to explain that the separation of powers is not only about dividing legal powers between institutions. It also focuses on how courts, legislatures, and executives should perform their different roles while working together without allowing one institution to dominate the others.

Why constitutional roles matter

When a court hands down a sweeping ruling, critics sometimes say that it has legislated. When a president acts without waiting for the legislature, the charge is that the executive has made law for itself. Those accusations are interesting because they often arise even when the legal question is complicated and the institution can point to some source of authority. The complaint is not always that the branch had no power at all. It is that the branch acted like the wrong kind of institution.

That problem is one of the questions that led me to write Gods, Judges, and Presidents. I was interested in the durability of the familiar three-part picture of government and in the possibility that judicial, executive, and legislative authority survive in our political imagination as recognizable roles as well as legal offices. Plato became important to the argument for an unusual reason. He was not describing modern constitutional government. He was asking a much older question about what happens when the different parts of a political order stop doing the work proper to them.[1]

I do not think the American founders copied a hidden Platonic plan, and nothing in the Republic gives us a ready-made doctrine of judicial review or presidential power. The connection is looser and, for that reason, more useful. Plato gives us a way to ask whether political order depends on different forms of action remaining different, even while they have to work together.

Plato's city and soul

Socrates begins the Republic by asking what justice is. Because justice is hard to see in a single person, he proposes looking first at a city, where the same problem might appear on a larger scale. The dialogue eventually distinguishes rulers, auxiliaries, and producers in the city, and reason, spirit, and appetite in the soul.[2]

A modern constitutional reader does not need to accept Plato's social hierarchy to notice the structural thought behind it. In Book IV, justice is connected with each part doing its own work and with the parts being ordered toward the good of the whole. Reason deliberates. Spirit gives force to conviction and makes action possible. Appetite encompasses the many needs and desires through which ordinary life is carried on. Trouble begins when one part ceases to be a part and tries to dominate everything else.[3]

That is more subtle than telling everyone to stay in a lane. Plato is not praising isolation. Reasons that cannot move anyone to act is useless. Spirit without judgment becomes reckless. Appetite cannot simply be abolished, because a city exists in part to answer ordinary human needs. The parts differ, but they are also dependent on one another. That combination of difference and dependence is close to the difficulty that modern separation of powers has always faced.

The branches are different kinds of judgment

The analogy with modern government has limits from the beginning. Courts are not Plato's reason, executives are not his spirited element, and legislatures should not be reduced to appetite. Still, the comparison becomes suggestive if we think about institutional habits. Courts are expected to give reasons that can be defended as law rather than preference. Executives are designed to direct administration and to act with some degree of unity and speed. Legislatures are places where interests, local demands, economic needs, and conflicting accounts of the public good are made visible and negotiated.

The last comparison requires care. Calling attention to the appetitive side of political life is not a way of belittling democratic representation. Plato's appetites include the ordinary wants that make social life possible. Food, property, work, exchange, family needs, and material security do not disappear because political theory finds them inelegant. A representative legislature has to encounter that untidy plurality. Its democratic value lies partly in being exposed to claims that a court may properly disregard and that an executive cannot simply command away.

Constitutional design, therefore, creates different settings for different kinds of judgment. A courtroom disciplines an argument in one way. A cabinet meeting does so in another. A legislative chamber does something different again. Tenure, procedure, publicity, elections, professional norms, and institutional memory all shape the decisions that emerge from those settings. Offices do not merely give people power. Over time, they teach officeholders how that power is supposed to be exercised.

Montesquieu, Madison, and the problem of overlap

Modern accounts of the separation of powers usually begin with Montesquieu and Madison. Montesquieu connected liberty with keeping legislative, executive, and judicial power from being concentrated in the same hands. Madison, writing about the proposed American Constitution, knew that a workable system could not keep the departments completely apart. His concern was the accumulation of the whole power of one department in the hands of another. The answer was a structure in which branches would remain distinct while checking one another.[4]

The American Constitution accordingly contains an overlap almost everywhere. The President can veto legislation. The Senate participates in appointments and treaties. Courts interpret statutes enacted by Congress and applied by the executive. If the doctrine required three sealed boxes, the constitutional text itself would violate it.[5]

Looking at roles helps make sense of that apparent contradiction. An institution can participate in another branch's work without becoming that branch. The Senate does not become an executive office when it considers a nomination. The President does not veto a bill by returning it with objections. A court does not become a legislature simply because a judgment has large consequences for public policy. The harder question is whether the institution is still acting through the forms of responsibility and judgment that make its role recognizable.

A comparative question

That question becomes clearer once we leave the United States. Parliamentary systems openly combine personnel who, in the American scheme, belong to different branches. A prime minister may sit in Parliament and lead the executive at the same time. Yet governing, legislating, and adjudicating remain distinguishable activities. Formal separation can be weaker while the differences among constitutional roles remain strong.

India makes the point especially well. The Supreme Court of India has long rejected an absolutely rigid version of separation of powers while insisting that the functions of the different organs remain sufficiently differentiated. In a 2026 judgment, the Court again described the Indian arrangement as a significant functional separation rather than a set of watertight compartments. That language is useful because it directs attention away from a diagram and toward the work institutions actually perform. The comparative question is not whether every constitution reproduces the American branches. It is how a constitutional system keeps different kinds of public judgment in relation without allowing one to swallow the others.[6]

Polybius offers another way into the same problem. His account of the Roman Republic described consuls, Senate, and people as mutually dependent parts of a mixed constitution. Those categories are not the legislative, executive, and judicial powers. That difference matters. Political thinkers have returned to three-part structures for many reasons, including social orders, forms of rule, psychological capacities, and legal functions. The recurrence does not prove that three is a magical constitutional number. It does show how often political thought has tried to secure order by distinguishing kinds of authority and then forcing them to live together.[7]

Where Plato stops helping

There are good reasons not to push the Platonic comparison too far. The ideal city of the Republic is hierarchical and deeply suspicious of democratic choice. Modern constitutional government rests on political equality, rights, representation, and popular sovereignty in ways that Plato did not anticipate and often would not have welcomed. Institutions also refuse to remain inside neat philosophical categories. Executives interpret the law. Legislatures investigate and judge qualifications. Courts administer their own systems and sometimes make rules with broad practical effects.

For that reason, I treat Plato as a diagnostic aid rather than a source of constitutional answers. The analogy will not decide a separation-of-powers case. It can help explain why the arguments in those cases so often turn on language about role. To accuse a judge of legislating is usually to say more than that the judgment changed public policy. It is to say that the judge chose in a manner associated with political lawmaking rather than legal judgment. To accuse an executive of bypassing the legislature is likewise to object to the replacement of representation and bargaining with command.

The character of constitutional power

Constitutions work through more than clauses. People learn to recognize a court, a legislature, or an executive office through rituals, procedures, habits, and expectations. Robes, hearings, elections, vetoes, legislative debate, and reasoned opinions all signal different forms of public authority. These forms can change, and they can certainly be abused, but they help make constitutional power intelligible to the people subject to it.

This is where Plato remains useful. The Republic treats justice as an ordering of parts that are neither interchangeable nor self-sufficient. Montesquieu connects differentiated power to liberty. Madison adds rivalry, incentives, and checks. Modern constitutional systems turn those ideas into offices and procedures. One argument of my book is that something is lost when we describe that architecture only as a distribution of legal competencies. Constitutional offices also carry inherited pictures of what judging, governing, and legislating are supposed to look like.[8]

Separation of powers is therefore not simply an eighteenth-century arrangement that modern governments have inherited out of habit. It is an ongoing effort to preserve differences among forms of authority that must nevertheless govern the same community. The branches cannot avoid touching one another, and no serious constitutional system asks them to. What matters is that their overlap does not erase their character. A republic does not need three institutions that never meet. It needs institutions distinct enough that none can plausibly present itself as the whole political order.

[1] Charles Lincoln, Gods, Judges, and Presidents: Trifunctional Archetypes in American Law and Government, chs. 1, 3, 7 (Bloomsbury Academic 2026).

[2] Plato, Republic 368d-369a, 414b-415d, 436a-441c (Paul Shorey trans., Harvard Univ. Press 1935).

[3] Id. at 433a-434c, 441d-444a.

[4] Montesquieu, The Spirit of Laws bk. XI, ch. 6 (Thomas Nugent trans., 1758); The Federalist Nos. 47, 51 (James Madison).

[5] U.S. Const. art. I, sec. 7; art. II, sec. 2; art. III, sec. 1.

[6] Ashwini Kumar Upadhyay v. Union of India, W.P.(C) No. 943 of 2021, paras. 22-25 (S.C. Apr. 29, 2026); Rai Sahib Ram Jawaya Kapur v. State of Punjab, AIR 1955 SC 549; Kesavananda Bharati v. State of Kerala, (1973) 4 SCC 225.

[7] Polybius, The Histories 6.11-18 (W.R. Paton trans., Harvard Univ. Press 1923).

[8] Lincoln, supra note 1, chs. 3, 7, and Conclusion.