Few concepts in constitutional discourse carry more rhetorical weight—and less analytical precision—than the rule of law. Politicians invoke it to justify austerity and to demand redistribution. Judges appeal to it when striking down legislation and when deferring to legislative judgment. Authoritarian regimes claim fidelity to it even as they imprison dissidents. The phrase operates as a kind of constitutional shibboleth: everyone professes allegiance, yet the commitments that allegiance entails remain profoundly contested.

This ubiquity should provoke suspicion rather than comfort. When a single concept can be deployed to defend constitutionalism and to legitimate its subversion, we must ask whether it retains any determinate meaning at all—or whether it has become, as Judith Shklar once suggested, little more than a self-congratulatory expression of political approval. The question is not merely semantic. How we define the rule of law determines what constitutional constraints we recognize, what institutional arrangements we demand, and whose claims to legal authority we treat as legitimate.

What follows is an examination of the concept's internal architecture. By distinguishing its formal from its substantive dimensions, by separating the rule of law from rule by law, and by interrogating the strategic uses to which the concept is put, we can begin to assess whether the rule of law still does meaningful theoretical work—or whether it has become constitutional theory's most sophisticated empty vessel.

The most fundamental cleavage in rule-of-law theory runs between formal and substantive conceptions. Formal or "thin" accounts, associated most prominently with Lon Fuller and Joseph Raz, focus on law's structural attributes: generality, prospectivity, clarity, consistency, promulgation, stability, and the congruence between official action and declared rules. On this view, the rule of law is essentially a set of conditions that law must satisfy to function as law—to guide conduct effectively. It says nothing about the content of legal norms. A legal system that efficiently enforces unjust rules can satisfy the formal rule of law.

Substantive or "thick" conceptions reject this austerity. Theorists like Ronald Dworkin and, in a different register, John Rawls insist that the rule of law necessarily incorporates requirements of justice, rights protection, and democratic legitimacy. For Dworkin, law is an interpretive enterprise governed by principles of integrity; a legal order that systematically violates fundamental rights cannot claim to embody the rule of law, regardless of how formally impeccable its statutes appear. Rawls similarly treats certain constitutional essentials—basic liberties, fair equality of opportunity—as prerequisites of legitimate legal order rather than optional additions.

The stakes of this disagreement are enormous. If we adopt a thin conception, then the rule of law becomes a relatively modest demand: whatever you do, do it through properly structured legal norms. This permits moral criticism of law's content from outside the rule-of-law framework, but it also means that deeply oppressive regimes can satisfy the principle. If we adopt a thick conception, the rule of law becomes a powerful tool for constitutional critique—but at the cost of collapsing the distinction between legality and justice, between what law is and what law ought to be.

Neither position is without serious theoretical difficulty. Thin conceptions face the embarrassment of apartheid South Africa, which operated through formally valid, prospective, general legal norms that were nonetheless instruments of systematic racial domination. Thick conceptions face the problem of indeterminacy: whose theory of justice gets incorporated into the rule of law? When American conservatives and progressives both claim the rule of law mandates their preferred constitutional interpretation, the concept threatens to dissolve into partisan assertion dressed in jurisprudential clothing.

Perhaps the most productive approach recognizes that formal and substantive requirements exist on a continuum rather than as binary alternatives. Fuller himself acknowledged that law's formal morality exerts pressure toward substantive decency—a regime that must publicize its rules, apply them consistently, and allow citizens to plan their lives around them will find it difficult to sustain arbitrary tyranny indefinitely. The formal attributes of law are not normatively inert; they embed modest but real substantive commitments. The question, then, is not whether the rule of law has substantive implications, but how far those implications extend and who gets to determine their content.

Takeaway

The rule of law is not a single principle but a spectrum of commitments—from minimal formal requirements to robust substantive demands—and the position one occupies on that spectrum determines which constitutional arrangements count as legitimate.

A distinction even more fundamental than the formal-substantive divide separates the rule of law from rule by law. The former demands that law constrain all exercises of power, including sovereign power itself. The latter treats law merely as an instrument through which sovereign will is expressed and enforced. The difference is structural: in a genuine rule-of-law order, the sovereign is bound by legal norms it did not unilaterally create and cannot unilaterally alter; under rule by law, the sovereign wields legal form as a tool of governance while remaining above or outside the legal order.

This distinction has deep roots in the Western constitutional tradition. Bracton's medieval dictum that the king is sub Deo et lege—under God and the law—articulates the aspiration that even supreme political authority is not self-legitimating. The American constitutional settlement, with its written constitution, separation of powers, and judicial review, represents one institutional attempt to realize this aspiration. But the distinction is far more fragile than constitutional triumphalism suggests. Every legal order must ultimately rest on some authority that defines the rules of the game. If that authority is itself constituted by law, then a deeper authority constitutes that law, generating an infinite regress. If it is not constituted by law, then the legal order rests on something extra-legal—a revolution, a constitutional convention, a mythologized founding moment.

This is the problem that Hans Kelsen attempted to resolve with his Grundnorm and that H.L.A. Hart addressed through the concept of the rule of recognition. Both theories acknowledge that legal systems require a foundational norm that cannot itself be legally validated. The rule of law, then, always operates within a framework whose foundations are not themselves governed by law. Sovereignty, in some form, persists beneath the constitutional surface. The question is whether constitutional design can so thoroughly institutionalize checks on sovereign power that the distinction between rule of law and rule by law becomes practically meaningful even if it cannot be theoretically absolute.

Contemporary constitutional crises make this question urgently practical. When executives govern through emergency powers, when legislatures pack courts to control constitutional interpretation, when ruling parties rewrite electoral rules to ensure their permanence—these are instances where the machinery of law is deployed to concentrate rather than constrain power. The formal apparatus of legality remains intact. Statutes are passed, courts issue rulings, official gazettes are published. Yet the animating principle—that law binds power rather than serving it—has been hollowed out. This is rule by law masquerading as the rule of law, and it is far more common in constitutional history than the celebratory narratives acknowledge.

Rawlsian constitutional theory offers one response to this challenge. By distinguishing constitutional essentials from ordinary legislation and insisting that the former reflect principles that free and equal citizens could reasonably accept, Rawls attempts to anchor the rule of law in a theory of political legitimacy that transcends mere sovereign will. But even this sophisticated framework depends on institutions—independent courts, a free press, an engaged citizenry—capable of enforcing the distinction between law that constrains power and law that merely channels it. The rule of law, it turns out, is not a self-executing principle. It is a political achievement, constantly vulnerable to erosion by the very power it seeks to constrain.

Takeaway

The rule of law promises that power is bound by law rather than merely exercised through legal form—but this promise depends on institutional arrangements that are themselves products of power, making the principle an ongoing political achievement rather than a settled constitutional fact.

If the rule of law meant one determinate thing, political actors would sometimes find themselves on its wrong side and would have to argue against it openly. Instead, virtually every political position claims the rule of law as its ally. Progressives invoke it to demand judicial enforcement of individual rights against legislative majorities. Conservatives invoke it to insist on textual fidelity and democratic self-governance against judicial activism. Populist leaders invoke it to legitimate constitutional transformations that undermine independent institutions. International development agencies invoke it to prescribe institutional reforms that happen to align with liberal market economies. The concept's very universality raises the question of whether it has become, in Brian Tamanaha's phrase, an "exceedingly thin" notion that everyone endorses precisely because it can mean almost anything.

This rhetorical promiscuity is not merely an intellectual curiosity; it has real consequences for constitutional governance. When authoritarian regimes claim to uphold the rule of law—pointing to their functioning courts, their published statutes, their formal adherence to constitutional procedures—the international community faces a dilemma. If the rule of law is purely formal, these claims may be technically valid, and critique must appeal to some other normative standard. If the rule of law is substantive, then asserting a violation requires identifying whose substantive commitments count as canonical. In practice, rule-of-law discourse often serves as a vehicle for exporting particular constitutional models under the guise of universal principle.

The critical legal studies tradition has pressed this point with particular force. If the rule of law is a concept capacious enough to legitimate both the Warren Court's rights revolution and the Lochner Court's protection of economic liberty, both social democratic constitutionalism and neoliberal structural adjustment, then perhaps it functions less as a constraint on power than as a legitimation device—a way of converting contested political choices into the apparently neutral language of constitutional principle. On this view, invoking the rule of law is always a strategic act, and the question is not what the rule of law requires but whose interests a particular invocation serves.

This critique is powerful but ultimately overstated. The fact that a concept is contested does not make it meaningless. Democracy, equality, and freedom are all concepts subject to radically different interpretations, yet we do not conclude that they do no work. What the critique does demonstrate is that the rule of law cannot function as a free-standing argument. Invoking it is the beginning of a constitutional argument, not its conclusion. It opens rather than settles the question of what institutional arrangements, what distributions of authority, what substantive commitments a legitimate legal order requires.

A more sophisticated approach treats the rule of law as what W.B. Gallie called an essentially contested concept—one whose proper application is inherently disputable, but whose disputability is itself constitutive of its value. The ongoing argument about what the rule of law requires is not a defect in the concept but its central function: it forces political actors to justify their exercises of power in terms of legal principle rather than naked interest. That this justification can be strategic and self-serving does not eliminate its disciplinary force. It constrains the range of publicly defensible positions, creates argumentative burdens, and provides normative vocabulary for resistance. The rule of law may not determine outcomes, but it structures the constitutional conversation within which outcomes are contested.

Takeaway

When every political actor can claim the rule of law for contradictory purposes, the concept's value lies not in settling disputes but in structuring them—forcing power to justify itself in terms of principle, even when that justification is strategic and incomplete.

The rule of law is neither the robust constraint its champions celebrate nor the empty signifier its critics dismiss. It is a structuring concept—one that organizes constitutional discourse, imposes argumentative burdens on exercises of power, and provides vocabulary for critique, even as it remains irreducibly contested in application.

What emerges from this analysis is that the rule of law's theoretical indeterminacy is not a weakness to be overcome but a condition to be managed. Constitutional theory's task is not to fix the concept's meaning once and for all but to articulate the institutional conditions under which its contestation remains productive rather than purely strategic—where the argument about legality genuinely constrains power rather than merely decorating it.

The question that should haunt every constitutional theorist is not what does the rule of law require? but rather: under what conditions does invoking it actually matter? That distinction—between the rule of law as living constitutional practice and the rule of law as rhetorical ornament—may be the most important one constitutional theory can draw.