Fundamentals

What natural law is and why it was so important for liberalism

By Daniel Sardá · April 23, 2026

# What natural law is and why it was so important for liberalism

Natural law is one of the most important ideas for understanding classical liberalism, modern constitutionalism and several libertarian currents. Its underlying thesis is simple but powerful: there are principles of justice prior or superior to the law created by governments. This does not mean “law of nature” in the physical sense, but a moral, rational or objective norm that allows one to judge whether a human law is just or unjust.

The *Stanford Encyclopedia of Philosophy* on theories of natural law explains that this tradition understands law not only as a social fact produced by institutions, customs or authorities, but also as a set of normative reasons for action. Put more directly: a law may exist, be written down and be enforced by the state, but that does not automatically make it just.

For liberalism, this idea was decisive. It made it possible to affirm that liberty is not a concession of the state, but a prior requirement of justice. If individuals have rights prior to political power, then no government can claim absolute authority over their lives, liberties and property.

The central thesis can be summarised like this:

Natural law was important for liberalism because it made it possible to affirm that liberty is not a concession of the state, but a prior requirement of justice: political power is legitimate only if it protects rights prior to itself.

What natural law means

Natural law holds that there are moral or legal principles that do not depend exclusively on human legislation, custom or the decision of the sovereign. Its starting point is that there is a difference between what power commands and what justice requires.

In simple terms:

The difference is crucial. From the perspective of natural law, a law may be valid within the positive legal system and still be unjust. For example, a rule approved by a majority, signed by a competent authority and applied by courts may violate basic moral principles if it unjustly destroys a person’s life, liberty, property or dignity.

This idea is fundamental for liberalism because it makes it possible to say:

One clarification is useful from the outset: natural law is not a single closed doctrine. It is a broad family of theories. There are classical, Christian, scholastic, modern rationalist, Lockean, libertarian and contemporary versions. What they share is the idea that human law can be evaluated in light of standards of justice that do not depend only on the power that enacted it.

Natural law and positive law: what is the difference

The distinction between natural law and positive law helps organise the whole debate.

Positive law is the law produced by human institutions: constitutions, laws, decrees, regulations, judicial decisions. It is the law that exists in a specific country, at a specific time, under specific authorities.

Natural law, by contrast, asks a different question: is that positive law just? Does it respect the life, liberty, property, conscience and dignity of persons? Or is it merely an order backed by force?

From a strictly positivist view, an unjust law may still remain legally valid if it was created through recognised procedures. From a natural-law view, that answer is insufficient: a norm may be legal and yet morally illegitimate.

This difference was essential to the liberal tradition because it made it possible to criticise:

Without some form of natural law or of rights prior to power, liberty is left much more exposed to the will of the legislator, the sovereign or the majority.

From natural law to natural rights

Two related, but not identical, concepts must be distinguished.

Natural law

It is the idea that there exists a rational, objective or universal moral order that allows one to judge human actions and positive laws.

Natural rights

These are individual claims, liberties or immunities derived from that moral order.

An example helps:

This transformation was decisive for liberal modernity. The ancient and medieval tradition spoke above all of an objective moral order, a natural justice or a rational law inscribed in human nature. Liberal modernity took part of that legacy and reformulated it as a theory of individual subjective rights.

*Britannica*’s summary of how natural law was transformed into natural rights explains that the modern conception of natural law as the source of natural rights was developed especially by thinkers of the seventeenth and eighteenth centuries.

That shift was politically explosive. It was no longer only a matter of saying that a higher justice existed. It was a matter of affirming that each individual could invoke rights against power.

Historical antecedents of natural law

Liberalism did not invent natural law. It inherited it, transformed it and turned it into an especially powerful political tool.

The classical world

In Greek and Roman philosophy there appears the idea that there is a justice superior to the particular laws of each city. This intuition is associated with Stoicism, universal reason, the common law of humanity and the distinction between natural justice and convention.

The basic idea was that the law of a polis or an empire did not exhaust justice. There could be rational or natural principles standing above local decisions.

Christianity and scholasticism

In the medieval Christian tradition, especially in Thomas Aquinas, natural law was linked to human reason, eternal law and the capacity of the person to know basic principles of justice. Natural law was not mere instinct or arbitrary command: it was a rational participation in a superior moral order.

This tradition made it possible to hold that the ruler, too, was subject to a moral order. Authority could not do just anything merely because it possessed power.

The School of Salamanca

The School of Salamanca mattered because it connected natural law with very concrete problems of political legitimacy, just war, dominion, property, commerce and the rights of indigenous peoples. Authors such as Francisco de Vitoria, Domingo de Soto and Francisco Suárez helped develop a tradition that imposed moral limits on imperial and political power.

Its relevance for later liberalism should not be exaggerated as if they were modern liberals, but it should be recognised: they contributed to a tradition in which political power could be judged by principles higher than its own will.

Early modernity

With authors such as Hugo Grotius, Samuel Pufendorf and later John Locke, natural law became more secularised, contractualist and oriented toward individual rights. This transition was gradual:

That path prepares the ground for classical liberalism.

John Locke and the liberal basis of limited government

John Locke is the most important author for understanding the connection between natural law and classical liberalism. The *Stanford Encyclopedia* on Locke’s political philosophy explains that Locke held that human beings are by nature free and equal, and that they have rights to life, liberty and property on a basis independent of the laws of any society.

This is decisive. Locke does not present rights as a concession of the monarch or as a permission of positive law. He presents them as rights that exist before government and that justify the very existence of government.

The Lockean core

In Locke, the basic architecture is this:

The clearest editorial formula is this:

Locke turned natural law into a liberal political theory: rights are not born from the state; the state is born to protect them.

Locke and property

Property is one of Locke’s most important and also most debated points. For him, property is not reduced to external things. It includes a broader idea of “property” over one’s own person, liberty and goods.

The Internet Encyclopedia of Philosophy on Locke’s political philosophy explains that Locke links property with self-ownership, labour and appropriation. The basic argument is that the person has dominion over himself and over his labour; by mixing his labour with external resources, he can acquire property.

This idea was fundamental for classical liberalism because it offered a moral defense of:

But it also opened difficult debates: original appropriation, common lands, indigenous peoples, inequality and Locke’s famous proviso of leaving “enough and as good” for others.

Locke and toleration

Locke was also decisive for liberty of conscience and religious toleration. *Britannica*, in discussing Locke’s political philosophy, notes his importance in the defense of liberty of conscience as a natural right.

This point broadens the picture of Locke. He is not only an author of property. He is also a central author for the liberal idea that individual conscience should not be absorbed by political or religious power.

Natural rights, property and political consent

Classical liberalism needed an answer to a central question: why must political power be limited?

Natural law offers a strong answer: because individuals have rights prior to the state. Government does not own the person. It does not create life, liberty or property from nothing. Its legitimate function is to protect those goods, not to absorb them.

From that follow three liberal pillars.

1. Individual rights

Individuals possess a morally protected sphere against power. That sphere includes life, liberty, conscience, property and legal security.

2. Political consent

If persons are naturally free and equal, no one is born with natural authority over them. Political power must be justified through consent, delegation or political compact.

The Internet Encyclopedia of Philosophy on Locke summarises this point well: government has obligations toward citizens, limited powers and may be overthrown under certain circumstances.

3. Limited government

Government cannot do just anything. It is limited by the purpose that justifies it: the protection of rights. If it becomes a systematic threat to those rights, it loses legitimacy.

This structure is one of the most important bases of liberal constitutionalism.

The influence of natural law on the Atlantic revolutions

Natural law did not remain confined to philosophical treatises. It became revolutionary political language in the Atlantic world.

The American Revolution

The United States Declaration of Independence translated the language of natural law into political claims of enormous impact: natural equality, unalienable rights and government based on the consent of the governed.

The *Stanford Encyclopedia* on John Locke notes that radical theories of natural rights influenced the ideologies of the American and French revolutions. That influence does not mean that the whole revolutionary process can be reduced to Locke, but it does mean that the language of natural rights was decisive for justifying the break with imperial power.

The French Revolution

The Declaration of the Rights of Man and of the Citizen also uses the language of natural rights: liberty, property, security and resistance to oppression. Here natural law appears as the basis of a new political legitimacy against the ancien régime.

Spanish America

In Spanish America, the language of natural law, sovereignty, representation and rights also formed part of the emancipatory vocabulary. But here it appeared mixed with other traditions: scholasticism, the constitutionalism of Cádiz, republicanism, political Catholicism and Atlantic liberalism.

That is why an oversimplified explanation should be avoided. Natural law was one important part of the political repertoire of emancipation, but not the only one.

Why natural law mattered for liberalism

Because it imposes moral limits on the state

Without natural law, law risks being reduced to what the sovereign commands. With natural law, positive law can be criticised as unjust.

This makes it possible to defend:

Liberalism needs that distinction because it does not accept that power is just merely by being legal.

Because it grounds individual rights

Liberalism needs to explain why the individual has a sphere that power must not invade. Natural law offers an answer: because the person possesses dignity, rationality, moral agency or self-ownership prior to political authority.

*Britannica*’s entry on natural rights distinguishes natural rights from civil rights: natural rights are acquired inherently, by nature or by God, while civil rights are granted and guaranteed by the state.

That distinction is crucial for liberalism. If all rights were simply state concessions, the state could withdraw them with the same authority with which it granted them.

Because it supports political consent

If individuals are naturally free and equal, political power cannot justify itself as the natural dominion of some over others. It must be justified.

From that follow several liberal ideas:

Because it protects private property

Property is central to classical liberalism. In Locke, property includes life, liberty and goods. This makes it possible to ground morally:

Not all classical liberals understood property in exactly the same way. But the idea that property is not a simple state concession was a central piece of classical liberalism.

Because it limits the power of the majority

Liberalism does not fear only the monarch. It also fears the unlimited majority.

If natural rights exist, then a majority cannot legitimately:

*Britannica*’s entry on liberalism and rights connects liberalism with the idea that individuals have rights into which the state must not intrude if majoritarian democracy is to be meaningful.

Because it allows one to distinguish legality and legitimacy

A state action may be legal and yet illegitimate. This point is essential for understanding:

Without that distinction, liberty becomes too dependent on whoever controls the legal apparatus.

Natural law and classical liberalism

In classical liberalism, natural law served as a foundation for:

Among the authors linked to this tradition appear:

A nuance is important, however: classical liberalism did not always depend exclusively on natural law. It also had utilitarian, evolutionist, historicist, constitutional and economic foundations. Some liberals defended liberty through natural rights; others, through consequences, prosperity, social peace, institutional evolution or limits on political knowledge.

But natural law was one of its most important columns.

Natural law and libertarianism: from Locke to Rothbard and Nozick

Many modern libertarian currents take from natural law a central premise: each individual has strong moral rights against other individuals and against the state.

The *Stanford Encyclopedia* on libertarianism summarises libertarianism as a theory centred on the permissible use of non-consensual force and on the idea that agents initially fully own themselves and may acquire property under certain conditions.

Robert Nozick

Robert Nozick developed a theory of rights as side constraints. The *Stanford Encyclopedia* on Nozick’s political philosophy explains that, for Nozick, a paradigmatic natural moral right imposes constraints on what others may do, even if violating that right would produce better aggregate results.

This matters because it shows a difference between rights-based libertarianism and utilitarianism. For Nozick, individuals are not mere pieces to be sacrificed for total welfare.

Murray Rothbard

Murray Rothbard tried to build a libertarian ethic grounded in natural law and natural rights. In *The Ethics of Liberty*, he explicitly relies on a Lockean-rooted tradition to derive a theory of property, contract, aggression and critique of the state.

In Rothbard, natural law becomes a radical defense of self-ownership, private property and the non-aggression principle.

Lysander Spooner

Lysander Spooner radicalised the principle of political consent. His best-known argument is that a constitution cannot morally bind as a contract those who have not personally consented to it. This is an extreme version of the liberal principle of consent: if government requires consent, that consent cannot be a hereditary fiction.

The libertarian formula

The connection can be summarised like this:

Rights-based libertarianism takes one classical liberal premise—the individual has rights prior to the state—and carries it toward a much more radical critique of political power.

Internal tensions of natural law within liberalism

Natural law was very important for liberalism, but it is not free of problems. A serious piece should include its tensions.

Universalism and pluralism

Natural law affirms universal principles. But modern societies are morally plural. This opens difficult questions:

Liberalism needs strong rights, but it also has to avoid turning one particular moral doctrine into absolute power.

Negative rights and positive rights

Classical liberalism usually uses natural law to defend negative rights:

But other currents have used the language of natural rights or human rights to defend positive rights:

This generates a central dispute: does natural law require above all abstention from harm, or also positive provision organised politically?

Property and original appropriation

The Lockean theory of property raises complex debates:

These debates remain important for libertarians, liberal egalitarians and critics of proprietary liberalism.

Natural law and slavery

Historically, many societies that spoke of natural rights coexisted with slavery, the exclusion of women, property qualifications and colonialism.

This does not automatically invalidate the doctrine, but it does force a distinction between:

One thing is the force of the idea. Another is the coherence of those who proclaimed it.

Religious and secular natural law

Some versions of natural law derive their principles from God. Others derive them from:

This matters because not all liberals justify natural law religiously. There are also rationalist, secular or philosophical defenses.

Critiques of natural law

Positivist critique

Legal positivism holds that the validity of law depends on recognised social sources, not on its morality. From this perspective, an unjust law may still remain legally valid if it was produced according to the rules of the system.

The positivist does not necessarily defend that law morally. What he says is that moral criticism and legal validity are different questions.

Historicist critique

The historicist critique holds that what we call “natural rights” varies historically and reflects concrete cultural contexts. From this view, many rights presented as universal may be products of an era, a class, a religion or a particular civilisation.

Utilitarian critique

Some liberals, such as Jeremy Bentham, rejected natural rights as rhetorical fictions. From a utilitarian perspective, institutions should be evaluated by their consequences for welfare, not by pre-political rights.

This critique matters because it shows that not all liberalism depends on natural law. There are consequentialist and utilitarian liberalisms as well.

Communitarian critique

The communitarian critique holds that the individual of liberal natural law is too abstract, too detached from community, tradition, history and concrete ties. According to this objection, the real person does not appear as an isolated individual, but as a member of moral and cultural communities.

Marxist critique

The Marxist critique interprets liberal natural rights as a juridical expression of bourgeois proprietary individualism. From this angle, liberal rights would formally protect liberty while materially consolidating relations of property and inequality.

Internal liberal or libertarian non-natural-law critique

There are also critics within the liberal camp. Some liberals and libertarians do not base their defense of liberty on natural law, but on:

Hayek, for example, is more sceptical of strong rationalist constructions and prefers evolutionary and institutional arguments about liberty and social order.

Liberal defense of natural law against its critiques

Despite those critiques, natural law still has strong defenses within liberalism.

1. Without a higher moral standard, law remains too close to power

If every valid law is simply what power produces, it becomes harder to condemn deeply unjust laws. Natural law offers a criterion for saying: “this may be legal, but it is not just.”

2. It protects minorities and individuals against majorities

Natural rights make it possible to maintain that neither the state nor the majority may do just anything to the individual. There are limits prior to collective decision.

3. It allows unjust laws to be condemned even when they are legal

This is one of its most important functions. It serves to judge slavery, religious persecution, confiscation, torture, censorship or punishment without due process, even when such practices have been legalised.

4. It does not necessarily require a closed religious metaphysics

Natural law can be formulated through practical reason, human agency, dignity, sociability or basic human goods. Not all of its versions depend on a specific theology.

5. Bad historical application does not destroy the principle

That a society may have proclaimed natural rights while excluding slaves, women or minorities does not necessarily prove that natural rights are false. It may prove incoherence, hypocrisy or limited application. In fact, the universal language of rights later made it possible to criticise those exclusions.

What remains today of natural law in liberalism

Today natural law does not occupy the same place it had in the seventeenth and eighteenth centuries, but its imprint remains deep. Many modern ideas depend, directly or indirectly, on that tradition:

Contemporary liberalism does not need to be exclusively natural-law based in order to recognise that inheritance. Even many liberal theories that do not explicitly use the language of natural law still work with a similar intuition: the individual does not belong to the state, and political power must justify its invasions of liberty.

What can be stated solidly and what requires caution

Solid claims

Claims requiring caution

False. There are utilitarian, historicist, evolutionist and institutionalist liberalisms.

False. There are natural-law theories that are not libertarian.

Anachronistic. Locke was an important basis for classical liberalism, but not a contemporary libertarian.

False. They open debates about scope, conflicts of rights, property, coercion and common goods.

Conclusion

Natural law was decisive for liberalism because it offered a moral basis for limiting political power. If individuals have rights prior to the state, then no authority can claim absolute legitimacy over their lives, liberties and properties.

Modern liberalism did not invent natural law, but it did transform it. From a doctrine about an objective moral order, it became a theory of individual rights capable of justifying constitutionalism, property, political consent and resistance against tyranny.

That is why natural law still matters. Not because it resolves every debate, nor because it is a simple and undisputed doctrine, but because it raises a question that liberalism cannot abandon:

Are there moral limits on power even when that power takes legal form, political-majority form or state-authority form?

The classical liberal answer was clear: yes. And that answer remains one of the strongest defenses of individual liberty against the absolute state, the unlimited majority and unjust law.