Introduction: The Fundamental Question

“What is law?” This apparently simple question has divided thinkers for millennia. It is not merely a technical matter for lawyers: it is a profound philosophical question about the relationship between statute and morality, power and justice, what law is and what it ought to be. The answers given to it have structured entire traditions and determined how courts decide cases that affect real lives.

Two great currents dominate Western legal philosophy: natural law theory (or jusnaturalism), which affirms a necessary connection between positive law and superior moral or rational principles; and legal positivism, which insists on a conceptual separation between the law as it is and the law as it ought to be. The debate between these currents — deepened, transformed, and partly transcended in the twentieth century by Hart, Fuller, Dworkin, and Alexy — remains at the centre of contemporary legal-philosophical reflection.

Classical Natural Law

Aristotle and Natural Justice

Aristotle distinguished, in the Nicomachean Ethics (Book V), between legal political justice (established by convention and variable from place to place) and natural political justice (valid everywhere independently of whether it is recognised). This distinction inaugurates the central intuition of natural law theory: there is a normative dimension of law irreducible to the will of the legislator.

Cicero and the Universal Natural Law

In the Roman Stoic tradition, Cicero elaborated the idea of a universal lex naturalis: just law is right reason in conformity with nature, eternal and immutable. In De Republica and De Legibus, he argues that an unjust law is not properly law at all (lex iniusta non est lex) — a formulation that would echo for centuries.

Thomas Aquinas: The Great Medieval Synthesis

The most systematic formulation of classical natural law is that of Thomas Aquinas (1225–1274), especially in the Summa Theologiae (I-II, qq. 90–97). Aquinas distinguishes four kinds of law:

  1. Eternal law (lex aeterna): divine reason governing the universe
  2. Natural law (lex naturalis): rational creatures’ participation in eternal law — the first practical principles accessible by reason (do good, avoid evil)
  3. Human law (lex humana): derived from natural law by determination or conclusion, adapted to the circumstances of each community
  4. Divine law (lex divina): revealed through Scripture

An unjust human law — one contradicting natural law — does not bind the moral conscience, except to avoid scandal. This normative hierarchy structured the whole of subsequent Scholasticism.

Hugo Grotius and Modern Natural Law

At the opening of modernity, Hugo Grotius (1583–1645) made a crucial transition: in De Iure Belli ac Pacis (1625), he proposed that natural law would hold etsi Deus non daretur — even if God did not exist — since it is grounded in the rational and social nature of the human being. This secularisation of natural law opened the way for modern international law and for the social-contract theories of Hobbes, Locke, and Rousseau.

Bentham and the Law/Morality Separation

Jeremy Bentham (1748–1832) was the first to articulate clearly the conceptual separation between law as it is (law as it is, positive law) and law as it ought to be. He used this distinction to mount a systematic critique of English common law and to propose utilitarian reforms. Positive law is the set of norms enacted by the sovereign; its validity does not depend on its conformity with morality.

John Austin and the Command Theory

John Austin (1790–1859) systematised positivism in The Province of Jurisprudence Determined (1832). For Austin, law is the command of the sovereign — an order backed by the threat of sanction, issued by a political superior habitually obeyed by a society and not habitually obedient to any superior. This command theory has serious limitations (it poorly explains customary law, power-conferring norms, the obligation of sovereigns themselves) — limitations that H.L.A. Hart would systematise a century later.

Hans Kelsen and the Pure Theory of Law

The most rigorous and influential version of legal positivism is that of Hans Kelsen (1881–1973). In Pure Theory of Law (1st ed. 1934; thoroughly revised 2nd ed. 1960), Kelsen proposes a “pure” legal science — purged of sociological, psychological, and moral elements. The central points of Kelsen’s construction:

  • Basic norm (Grundnorm): at the apex of the normative hierarchy stands a hypothetical norm, posited by no real act of will, which serves as the logical-transcendental foundation of the entire legal order: “the historically first Constitution ought to be obeyed.” It is not valid — it is presupposed
  • Hierarchy of norms: the legal system is graduated (Stufenbau); each norm derives its validity from a higher norm. Constitution → statutes → regulations → administrative acts and judicial decisions. Validity is always a relation between norms, never between a norm and reality
  • Imputation, not causation: legal science does not describe what is (the domain of being, Sein) but what ought to be (Sollen). The legal norm imputes a consequence (sanction) to a condition (delict): it is not a causal law but a deontic one
  • Dynamic and static: dynamic theory deals with the validity of norms by the criterion of their creation according to established procedure; static theory analyses the logical structure of norms

Kelsen’s contribution was monumental: it definitively separated legal validity from moral validity and offered a formal model of the legal system that influenced generations of jurists across continental Europe and Latin America.

H.L.A. Hart: Refined Positivism

The Concept of Law (1961)

Herbert Lionel Adolphus Hart (1907–1992), Professor of Jurisprudence at Oxford, published The Concept of Law in 1961 — a work that simultaneously deepens, critiques, and transforms the positivist tradition. Against Austin, Hart demonstrates that the command theory is inadequate: it does not account for (a) power-conferring norms (marriage, wills, contracts), which are not commands backed by sanctions; (b) norms that bind the sovereign; (c) the continuity of law when the sovereign changes; (d) the difference between being obliged to do something (under threat) and having a legal obligation to do it.

Primary and Secondary Rules

Hart’s central innovation is the distinction between primary and secondary rules. Primary rules impose duties of conduct. Secondary rules are meta-rules about primary rules:

  • Rule of recognition: identifies which norms belong to the system. It need not be validated by another norm — it exists as a social fact, accepted by officials. It replaces the Kelsenian Grundnorm in a more empirically satisfying way
  • Rules of change: establish procedures for creating, altering, and repealing norms
  • Rules of adjudication: confer authority to settle disputes about the application of primary rules

A mature legal system is defined by the union of primary and secondary rules. Primitive societies have only primary rules, suffering from uncertainty (no criterion for identifying law), stasis (no mechanism for change), and inefficiency (no authoritative adjudication).

Open Texture and Discretion

Hart recognises that legal language has open texture: every general concept has clear cases of application and an inevitable penumbra of uncertainty where law does not determine the outcome. In these “hard cases,” judges create law by exercising discretion. This position will become Dworkin’s primary target.

The Hart–Fuller Debate (1958)

In the same volume of the Harvard Law Review in which Hart published “Positivism and the Fidelity to Law,” Lon Fuller (1902–1978) responded with “Positivism and Fidelity to Law — A Reply to Professor Hart.” The debate centred on Nazi law: Hart insisted that the Reich’s laws, however unjust, were valid law, and that moral criticism must be pursued on a separate plane. Fuller argued that law has an inner morality — a set of procedural requirements (generality, publicity, prospectivity, clarity, consistency, stability, congruence with official action) — without which one cannot even speak of “law.” These requirements, developed in The Morality of Law (1964), are not substantively moral but constitute the conditions of possibility of the legal phenomenon as such.

Ronald Dworkin: Law as Integrity

The Critique of Positivism

Ronald Dworkin (1931–2013) formulated, beginning with Taking Rights Seriously (1977), the most systematic and influential critique of Hartian legal positivism. The central argument: legal systems include not only rules (which apply in an all-or-nothing fashion) but also principles — normative standards such as “no one may profit from his own wrong,” which have weight and dimension and do not derive from any rule of recognition. If positivism cannot explain the presence and operation of principles in legal reasoning, it is wrong as a descriptive theory of law.

Rights as Trumps

In Taking Rights Seriously, Dworkin defends an egalitarian liberalism grounded in the principle of equal concern and respect: government must treat every citizen with equal concern — and this requirement generates individual rights that function as trumps against collective goals. No social welfare policy, no argument from efficiency or utility, can justify the violation of fundamental rights. This thesis has direct implications for judicial review: courts, in striking down legislation for rights violations, do not usurp democracy — they exercise their constitutional function.

Law’s Empire (1986): Interpretivism and Integrity

In Law’s Empire, Dworkin develops his interpretivist theory of law. Against positivism (“law is a set of facts determined by social sources”) and against natural law theory (“law is what morality requires”), Dworkin proposes that law is an interpretive practice: to understand law is to interpret a social practice with a history and a purpose.

Law as integrity requires judges to treat the system as expressing a coherent set of moral principles — to decide each case in a way that makes the body of law as a whole as coherent and morally justified as possible. The chain novel metaphor illuminates the process: the judge is like a novelist continuing another’s work — he must be faithful to what has already been written and, at the same time, make the work as good as it can be.

Judge Hercules — an ideal figure endowed with superhuman skill, time, and patience — represents the regulative ideal of legal reasoning. In hard cases, Hercules does not exercise discretion (against Hart): he finds the answer that best fits and best justifies existing law.

Robert Alexy (born 1945) represents a synthesis between the theory of rational practical discourse (Habermasian in inspiration) and legal theory. In A Theory of Legal Argumentation (1978) and A Theory of Constitutional Rights (1986), Alexy proposes that:

  • Legal norms of fundamental rights are not only rules but principles — optimisation mandates that order something to be realised to the greatest possible extent, given the factual and legal circumstances
  • When principles collide, the appropriate mechanism is balancing (Abwägung), guided by the “law of collision”: the relative weight of each principle in a concrete case determines which prevails
  • Law has a claim to correctness (Anspruch auf Richtigkeit) — it aspires to be correct, not merely efficacious. This claim necessarily connects law and morality (against strict positivism) without identifying them (against natural law theory)

Joseph Raz and the Authority of Law

Joseph Raz (1939–2022), Hart’s pupil at Oxford, developed an “exclusive” version of positivism. In The Authority of Law (1979) and The Morality of Freedom (1986), Raz argues that the legitimate authority of law resides in its capacity to act as an exclusionary reason: in certain conditions, obeying law is preferable to deliberating directly from first-order moral reasons — because a legitimate authority better crystallises the relevant practical reasoning than the individual could do alone. Against Dworkin, Raz insists that law is identifiable by its social sources (the “sources thesis”), without reference to morality.

Contemporary Discussion: Constitutional Interpretation

The positivism–anti-positivism debate takes renewed form in discussions of constitutional interpretation. Constitutionalists like Dworkin argue that interpreting the Constitution requires substantive moral reasoning — constitutional rights are moral principles that the interpreter must apply in their best light (moral reading of the Constitution). Positivists such as Raz and Andrei Marmor maintain that constitutional law has limits determined by its history and the intentions of its authors, and that expanding those limits through moral reasoning is legislation, not interpretation.

This tension — between originalism, interpretivism, and constitutional natural law — is today the most lively battleground in anglophone legal philosophy and resonates directly in constitutional debates across Brazil, Europe, and international law.

Conclusion: An Open Dispute

Western legal philosophy has traversed a long journey: from Aristotelian and Thomistic natural law, through Benthamite and Kelsenian positivism, to Hart’s analytical positivism and its transcendence by Dworkin and Alexy. But the fundamental debate remains open: what makes a norm law? Can an iniquitous norm be valid law? When judges decide hard cases, do they discover or create the law? Is there always a right answer?

These are not academic abstractions. They determine how constitutional judges interpret fundamental guarantees, how international tribunals try crimes against humanity, how legislators understand the limits of their power. Philosophy of law, in this sense, is philosophy with consequences.

← Articles