The Roots of Liberty: Natural Law and Classical Liberalism

Libertarian jurisprudence is often regarded as a modern legal theory, especially in its articulation by 20th-century thinkers like Murray Rothbard and Bruno Leoni. However, its intellectual lineage runs deep, rooted in the enduring tradition of natural law and brought to political maturity through classical liberalism. The core assertion of libertarian legal theory—that rights are prior to the state and derive from the nature of man—originates in the philosophical and legal revolutions of early modern Europe. In this essay, we explore the roots of liberty through the natural law tradition, focusing on the work of Hugo Grotius, John Locke, and Lysander Spooner, showing how their contributions laid the legal and philosophical foundation for a libertarian legal order.

I. Natural Law: The Foundation of Pre-Political Rights

Natural law theory asserts that there exists a moral order inherent in human nature and the structure of reality, discoverable through reason. It is a universal moral grammar that governs human conduct and informs our understanding of justice. Unlike legal positivism, which confines legality to what sovereign powers dictate, natural law holds that true law is rooted in reason and nature, not merely will and force.

As Aquinas put it, "lex naturalis est participatio legis aeternae in rationali creatura"—the natural law is the participation of the rational creature in the eternal law (Summa Theologica, I-II, Q. 91, Art. 2). For Aquinas and his intellectual heirs, human beings, by virtue of being rational and moral agents, are bound to obey a law higher than any man-made decree.

This vision was revived and adapted in the early modern period, most significantly by Hugo Grotius. Often regarded as the father of modern natural law and international law, Grotius sought to ground moral and legal norms in human nature itself—so firmly, in fact, that he famously stated these principles "would have a degree of validity even if we were to concede... that God did not exist" (De Jure Belli ac Pacis, Prolegomena, sec. 11). Grotius was not denying God’s existence but asserting that natural law is rationally discernible and binding apart from divine fiat.

This move made rights pre-political: they are not granted by the state or a sovereign but exist antecedent to civil authority. Law, then, must conform to the moral order already inscribed in the nature of human beings. From Grotius's vantage point, legal systems that fail to recognize these pre-political rights are not merely unjust—they are illegitimate.

II. John Locke and the Political Ordering of Natural Law

While Grotius gave natural law a rationalist and universalist framework, John Locke embedded these insights into a political theory that would become the cornerstone of classical liberalism and, by extension, libertarian thought. In his Second Treatise of Government (1689), Locke begins not with the state, but with the individual in a state of nature—a moral order without political institutions.

According to Locke, the state of nature is not a state of war or chaos, but of liberty, not license. It is a condition where individuals are free to dispose of their persons and property within the bounds of the law of nature, “which teaches all mankind... that being all equal and independent, no one ought to harm another in his life, health, liberty, or possessions” (Second Treatise, §6).

Locke’s contribution lies in two central doctrines:

1. Self-Ownership: Each individual owns himself by virtue of being a rational agent created by God. This self-ownership grounds the right to life, liberty, and estate. It is the foundation upon which all property claims are built.

2. Property through Labor: Locke famously argued that individuals acquire private property by “mixing their labor” with unowned resources. The moral basis for ownership, then, is not conquest or fiat, but productive action rooted in natural rights.

This Lockean view had a profound impact on Anglo-American legal and constitutional thought. The U.S. Declaration of Independence explicitly reflects Locke’s influence, asserting that individuals possess “unalienable Rights” and that governments are instituted “to secure these rights.”

Locke, unlike some libertarians, did believe in a limited government—what he called a "trust"—to protect natural rights. But this government was strictly circumscribed. When it violated the trust, it lost its legitimacy and could be resisted and overthrown. As he put it: “wherever law ends, tyranny begins” (Second Treatise, §202). This radical insight—that law is not what the sovereign says but what natural reason affirms—remains a bedrock principle of libertarian jurisprudence.

III. Lysander Spooner: Natural Law and Constitutional Skepticism

While Locke framed the liberal constitutional tradition, Lysander Spooner (1808–1887) offered a more radical libertarian vision in 19th-century America. Spooner, a lawyer, abolitionist, and natural rights theorist, extended natural law to its logical anarchist conclusions, challenging both state authority and constitutional orthodoxy.

In his seminal work, The Unconstitutionality of Slavery (1845), Spooner used natural law reasoning to show that any interpretation of the Constitution that permits slavery must be invalid, since no law can legitimize aggression against natural rights. He insisted that the Constitution, rightly read, was a document that presupposed justice—not power.

Later, in No Treason: The Constitution of No Authority (1867), Spooner attacked the very legitimacy of constitutional government altogether. His argument was simple yet devastating: no government can claim authority over individuals who did not voluntarily consent to its rule. Mere birth within a territory does not constitute a contract. Therefore, the U.S. Constitution, having never been explicitly agreed to by all it governs, has no binding authority. He wrote:

“A man is none the less a slave because he is allowed to choose a new master once in a term of years.” (No Treason, No. VI)

Spooner’s defense of natural law emphasized that justice precedes law, and that legality must conform to moral reasoning, not vice versa. His rejection of legal positivism foreshadowed the libertarian critique of majoritarianism and state monopolies on legal authority.

Importantly, Spooner also recognized the need for competitive legal institutions, arguing that individuals should be free to choose their adjudicators and laws, provided they do not infringe on others’ rights. In this, he anticipated later libertarian proposals for polycentric legal orders and voluntary governance.

IV. Rights as Pre-Political and Immutable

A common thread unites Grotius, Locke, and Spooner: the belief that rights are not given by the state, and cannot be justly taken by it. This view stands in opposition to the legal positivist tradition, represented by Hobbes and Austin, in which law is simply the command of a sovereign, enforced by threat.

In contrast, the natural law tradition holds that law must be discovered, not invented. As Murray Rothbard wrote:

“Natural law theory holds that there is a natural order of right and wrong, a structure of justice that inheres in the nature of man and the world.” (The Ethics of Liberty, p. 3)

This understanding grounds legal authority in objective moral truths, not in the arbitrary will of rulers. Because rights are prior to the state, law must be judged by its conformity to these pre-political principles. This is what distinguishes libertarian jurisprudence from both legal realism and progressivism, which treat law as a flexible tool for social engineering.

Libertarian jurisprudence, grounded in natural law, asserts that the role of law is not to perfect man or maximize welfare, but to protect liberty by prohibiting aggression. In this sense, law is a negative institution: it exists to define and enforce boundaries, not to create outcomes.

V. Classical Liberalism: Political Application of Natural Law

The 18th and 19th centuries saw the rise of classical liberalism, the political movement that sought to institutionalize the natural law principles articulated by Locke and others. Thinkers such as Montesquieu, Adam Smith, Thomas Jefferson, and later Frédéric Bastiat and Herbert Spencer, carried forward the belief that liberty, limited government, and private property were the essential components of a just society.

Frédéric Bastiat, in particular, captured the essence of libertarian legal philosophy in his short but powerful work The Law (1850):

“The law is the organization of the natural right of lawful defense. It is the substitution of a common force for individual forces to guarantee persons, liberties, and properties.” (The Law, p. 6)

When the state exceeds this function—when it becomes a tool of “legal plunder”—it becomes the very aggressor it was created to restrain. Bastiat’s definition of law as a defensive institution, not an affirmative instrument of redistribution, expresses the classical liberal ideal.

VI. Conclusion: The Moral Architecture of Libertarian Law

The jurisprudence of liberty finds its deepest roots in the tradition of natural law and classical liberalism. From Grotius’s universal rational order to Locke’s vision of individual rights and consensual government, to Spooner’s unyielding defense of natural justice over constitutional convention, libertarian legal theory arises as a coherent and principled alternative to statist legal models.

It is a view that asserts rights are inherent, not bestowed; that justice is discoverable through reason, not manufactured by decree; and that law must exist to protect liberty, not manage human life.

In an era dominated by legal positivism and bureaucratic instrumentalism, revisiting the natural law foundations of libertarian jurisprudence is not merely an academic exercise—it is a reclaiming of the moral structure that once animated the Western legal tradition. It is a reminder that liberty is not the gift of governments, but the birthright of all human beings.

References

• Aquinas, Thomas. Summa Theologica, I-II, Q. 91.

• Grotius, Hugo. De Jure Belli ac Pacis (On the Law of War and Peace), 1625.

• Locke, John. Two Treatises of Government, Second Treatise, 1689.

• Spooner, Lysander. The Unconstitutionality of Slavery, 1845; No Treason: The Constitution of No Authority, 1867.

• Rothbard, Murray. The Ethics of Liberty, 1982.

• Bastiat, Frédéric. The Law, 1850.