Relation between Eternal Law, Natural Law, and Human Law

The relationship between Eternal Law, Natural Law, and Human Law forms one of the most profound and enduring themes in the history of jurisprudence. These concepts are central to the philosophy of Thomas Aquinas, who integrated classical and Christian thought into a comprehensive theory of law. His framework presents law as a rational order guiding human behaviour toward the common good and moral perfection.

The Concept of Law in Thomistic Philosophy

According to St. Thomas Aquinas, law is defined as “an ordinance of reason for the common good, made by him who has care of the community, and promulgated.” He conceived the universe as governed by a divine rational order—Eternal Law—from which all other forms of law derive.
Aquinas distinguished four kinds of law:

1. Eternal Law – the divine order governing all creation.
2. Natural Law – the participation of rational beings in the Eternal Law.
3. Divine Law – the revealed law found in sacred scriptures.
4. Human Law – positive laws made by human authorities for social governance.

Among these, the interrelation of Eternal, Natural, and Human Law is of central importance in understanding the philosophical hierarchy of legal norms.

Eternal Law

Eternal Law represents the divine wisdom or rational plan of God that directs all creation toward its proper end. It is the highest form of law and forms the foundation of all order in the universe.
Key features of Eternal Law:

• It is universal and immutable, applying to all beings and all actions.
• It exists in the mind of God, who governs the cosmos through reason and purpose.
• It is not directly known in its entirety by human beings but is reflected in the order and purpose found in nature.
• Every law—natural or human—is valid only insofar as it conforms to the Eternal Law.

Thus, Eternal Law is the source and measure of all subordinate laws.

Natural Law

Natural Law is derived from and participates in the Eternal Law. It is the manifestation of divine reason within human reason. Aquinas described it as “the rational creature’s participation in the Eternal Law.”
Natural Law enables human beings, through reason, to discern what is right or wrong according to the moral order established by God. It provides a moral standard by which human conduct and human-made laws are to be judged.
Characteristics of Natural Law:

• It is accessible to human reason—individuals can discover it through reflection on human nature and the purposes of life.
• It is universal—binding on all people irrespective of culture or religion.
• It is unchanging and eternal, though its applications may vary with circumstances.
• Its primary precepts include the pursuit of good, preservation of life, reproduction, education of offspring, and living in society.

In essence, Natural Law represents the bridge between divine reason (Eternal Law) and human reason, allowing moral knowledge to guide human legislation.

Human Law

Human Law is the positive law enacted by human authorities to regulate the behaviour of individuals within society. It derives its legitimacy from Natural Law and, ultimately, from Eternal Law.
Aquinas viewed human laws as particular determinations of general principles of Natural Law. For example, while Natural Law commands that wrongdoers should be punished, Human Law specifies the nature and extent of the punishment according to social needs.
Features of Human Law:

• It must aim at the common good and promote justice and order.
• It derives authority from conformity with higher laws.
• It is mutable, as it can change to meet social circumstances, though it must remain consistent with Natural Law principles.
• If Human Law contradicts Natural or Eternal Law, it ceases to be true law and becomes an act of tyranny.

Aquinas famously declared, “An unjust law is no law at all” (lex iniusta non est lex), emphasising that legality must be consistent with morality.

Interrelationship between Eternal, Natural, and Human Law

The relationship among these three forms of law is hierarchical and participatory:

1. Eternal Law is the supreme source—the divine reason and ultimate order of the universe.
2. Natural Law is human participation in that divine order, discerned through reason.
3. Human Law is a further human articulation of Natural Law, expressed through positive enactments and legal systems.

This relationship can be represented as follows:

Thus, Human Law must reflect and implement Natural Law, which in turn is rooted in Eternal Law. Any deviation from this divine-natural hierarchy renders human legislation morally defective.

Practical Implications

The relationship between these laws has profound implications for jurisprudence and governance:

• Moral Basis of Law: It asserts that legal validity is not purely procedural but also moral. Laws contrary to natural justice lack moral force.
• Limitation of Sovereign Power: Human lawmakers are bound by higher moral principles derived from Natural and Eternal Law.
• Foundation of Human Rights: The modern concept of inherent human rights owes much to Natural Law theory, which posits universal moral rights preceding positive law.
• Judicial Interpretation: Courts often invoke natural law principles, such as fairness and reasonableness, to fill gaps or interpret legislation.

Criticism and Modern Relevance

Critics of the Thomistic hierarchy, especially legal positivists like John Austin and H. L. A. Hart, reject the idea that moral or divine law should determine legal validity. They argue that law derives authority from sovereign command, not from moral reasoning.
However, Natural Law continues to influence constitutional and international law, especially in areas such as:

• Human rights and humanitarian law.
• Environmental law and justice.
• Ethical foundations of legislation and governance.