Their Law of Nature (Natural Law) has served as the ultimate intellectual foundation for modern International Law. From Greek philosophy and Roman statecraft to medieval canon law and the treatises of Hugo Grotius, Natural Law provided the moral and rational scaffolding needed to govern relations between sovereign entities. Today, while positive international law dominates through treaties and customs, Natural Law remains deeply active as a judicial safety valve through equity, good faith, and the “general principles of law recognized by civilized nations” under Article 38 of the ICJ Statute.
1. Defining the Law of Nature: Conceptual Foundations
To understand how International Law evolved into a cohesive global system, one must first analyze the concept of Natural Law. Throughout legal history, Natural Law has been expressed through various synonymous terms:
- Divine Law: Principles imposed by God upon mankind.
- Law of Reason: Rules founded upon rational thinking and appealing to man’s innate intellectual capability.
- Unwritten Law: Law not enacted by human legislation, but inherently given by nature.
- Eternal Law: Principles that are everlasting, immutable, and universally true.
- Moral Law: Conscience-driven rules of conduct rooted in fundamental concepts of right and wrong.
Classical Definitions by Jurists and Philosophers
-
- John Salmond: Defined natural law as “principles of natural right and wrong—the principle of natural justice, if we use the term justice in its widest sense to include all terms of rightful action.”
- Cicero: Declared in classical Roman legal thought: “There is indeed a true law (lex), right reason agreeing with nature, diffused among all men, unchanging, everlasting… It is not one law at Rome and another at Athens, one law today and another hereafter, but the same law everlasting and unchangeable, will bind all nations at all times…”
“There is indeed a true law (lex), right reason agreeing with nature, diffused among all men, unchanging, everlasting… It is not one law at Rome and another at Athens, one law today and another hereafter, but the same law everlasting and unchangeable, will bind all nations at all times…”
-
-
- Justinian: Highlighted in his Roman codifications that Jura naturalia, established by divine providence, remains immutable, whereas civil law (Jus civile) changes via legislation or tacit consent.
- Christian Thomasius: Defined it as a divine law written in human hearts, obliging man to act consistently with rational nature.
-
2. The Fluid and Evolving Nature of Natural Law
Despite its claim to immutability, the content of Natural Law has varied across historical epochs. Because Natural Law relies on human reasoning, it is inherently influenced by human prejudices, moral values, political ideologies, religious convictions, and stages of civilization.
-
-
- Jeremy Bentham’s Critique: Bentham famously critiqued the subjectivity of Natural Law, remarking that people continually talk of nature only to project their personal sentiments of right and wrong as formal legal chapters.
- J.L. Brierly’s Insight: Brierly noted that in human conduct, Natural Law is relative to conditions of time and place. While a rational universe remains a necessary postulate of thought, human societies view the world through evolving perspectives across different centuries.
- Hans Kelsen’s Analysis: Kelsen argued that deducing “what ought to be” from “what is” constitutes a logical fallacy, leading different authors to derive contradictory principles based on their political creeds.
-
3. Historical Evolution Across Legal Systems
A. The Greek City-States (Jus Naturale)
Four centuries before the Christian era, Greek city-states developed an early international system governing war, peace, treaties, and permanent embassies under the sanction of Zeus.
- Aristotle’s Contribution: Aristotle distinguished between legal justice (man-made positive law) and natural justice (rules deriving force from human nature everywhere).
- Limitation: The Greek concept was partial and discriminatory; they applied the rules of Natural Law strictly among themselves, committing atrocities against “barbarians” due to a sense of cultural superiority.
B. The Roman Empire (Jus Gentium)
The Romans transformed Natural Law into practical legal machinery. To resolve disputes involving non-Roman merchants and subjects who lacked Roman citizenship, magistrates developed the Jus Gentium (law of nations).
- Integration of Reason: Roman judges applied natural justice to soften the rigor of strict civil law (Jus civile).
- Synthesis: Under Emperor Justinian, Jus gentium came to be viewed as synonymous with the law of nature established by natural reason among all mankind.
C. The Medieval Scholastic Period
In 9th to 14th-century Europe, the Christian Church held intellectual hegemony.
- St. Augustine & St. Thomas Aquinas: Aquinas argued that Divine Providence rules the world, dividing divine law into direct scriptural revelation and that which reveals itself to human reason (Natural Law).
- Just War Doctrine: Canonists like Aquinas and Giovanni da Legnano (De bello de represaliis et de duello, 1360) used natural reason to determine the lawfulness of war, establishing that war was permissible only for a just cause.
- Franciscus de Victoria (1480–1546): Victoria tested the rights of Spanish conquests and Indigenous populations in the Americas against natural reason and divine law.
4. The Precursors and the Grotian Revolution
The 16th century saw European politics dominated by Niccolò Machiavelli’s The Prince, which advocated force, treachery, and raw power politics unrestrained by moral rules. The resulting devastating conflicts forced European jurists to seek a higher, binding legal standard.
Key Precursors to Grotius
- Jean Bodin (1586): Defined sovereignty in De Republica as absolute power, yet explicitly argued that sovereign rulers remained bound by the laws of God, nature, and nations.
- Johannes Althusius: Opposed pure state absolutism, arguing that sovereignty originates from the people and is limited by natural law.
- Balthazar Ayala (1582): Formulated early systematic principles regarding the law of war and military discipline rooted in Natural Law.
- Francisco Suárez (1612): Authored Tractatus de legibus, introducing the concept of an international community of states governed by natural reason and custom.
- Alberico Gentili (1552–1068): Regarded as a crucial bridge to modern international law, Gentili used natural reason, Roman law, and state practice in works like De Jure Belli to treat international law as a living, rational organism.
Hugo Grotius: The “Father of International Law”
Hugo Grotius (1583–1645) integrated Natural Law, Roman law, and state practice into a unified jurisprudence.
- Definition of Natural Law: Grotius defined it as “the dictate of right reason, indicating that any act, from its agreement or disagreement with the rational nature, has in it a moral turpitude or a moral necessity…”
- Secularization of Law: Grotius asserted that Natural Law is discernible through right reason and would exist even if God did not exist.
- Dual Sources: He recognized both Natural Law and customary/volitional law (Jus voluntarium), asserting that in cases of direct conflict, Natural Law must prevail.
5. Post-Grotian Schools of Thought
Following Grotius, jurists split into distinct intellectual traditions regarding the authority of Natural Law:
|
Thinker / Jurist |
Core Theory on Natural Law in State Practice |
|---|---|
|
Thomas Hobbes |
Denied divine sanction; viewed Natural Law as self-preservation and justice. Declared that sovereign states exist in a perpetual “state of nature” (war of all against all). |
|
Samuel von Pufendorf |
Maintained that states, having no human superior above them, are strictly bound by the Law of Nature deduced through international reason. |
|
Emer de Vattel |
Divided International Law into Necessary Law (internal, immutable Natural Law binding state conscience) and Positive Law (Voluntary, Conventional, and Customary Law). |
6. Modern Application: How Natural Law Operates Today
While the 19th-century Positivist School attempted to reduce all legal authority to written state consent, the aftermath of World Wars I and II exposed the limits of strict positivism. International tribunals turned back to principles of equity and rational justice to resolve complex global disputes.
A. Article 38 of the ICJ Statute
The Statute of the International Court of Justice (ICJ) authorizes the Court to apply:
“The general principles of law recognized by civilized nations.”
Jurists like Georg Schwarzenberger note that this clause serves as the primary mechanism for transforming underlying principles of Natural Law into positive, enforceable International Law.
B. Key Judicial Precedents Utilizing Natural Justice & Equity
- Preferential Rights Claimed by Blockading Powers from Venezuela (PCA, 1904): The Permanent Court of Arbitration ruled that good faith (bona fides) is a fundamental requirement that must govern all international relations.
- Norwegian Claims Case (USA v. Norway, 1922): The tribunal interpreted “law and equity” as general principles of justice distinct from any single domestic legal system.
- Diversion of Water from the Meuse Case (PCIJ, 1937): Judge Hudson and the Permanent Court of International Justice confirmed that equitable principles form an integral part of the international legal framework applicable under Article 38.
- Eastern Extension, Australia and China Telegraph Co. Ltd. (1923): The British-American Claims Arbitral Tribunal held that where express treaty rules are silent, jurisprudence must resolve conflicts by applying general principles analogous to mathematical corollaries.
[ Gaps in Treaty / Customary Law ]
│
▼
[ Judicial Reason & Common Sense ]
│
▼
[ Principles of Equity, Fairness & Good Faith ]
│
▼
[ Modern Application of “Natural Law” Today ]
Conclusion
As Professor J.L. Brierly observed, when judges and international arbitrators confront novel legal scenarios not explicitly covered by written treaties, they inevitably apply judicial reason—the modern equivalent of what medieval jurists termed Natural Law.
Far from being an obsolete philosophical relic, Natural Law remains the dynamic engine that ensures International Law adapts to unforeseen global challenges with justice, equity, and reason.
Q1: What is Law of Nature in International Law?
It refers to universal moral principles that guide international legal systems.
Q2: Is natural law still relevant today?
Yes, it influences human rights and global justice systems.
