Classical and early modern

Natural Law Theory

Law gets its force from morality: a gravely unjust rule is not truly law, or not fully law.

Ancient Greece and Rome to today · Greece, Rome, medieval Europe, then worldwide. Spotted a mistake? Tell us.

Read this first. This is a first map of a large subject. Each school is a family of views, and its thinkers often disagree with one another, so every summary simplifies. We describe each school in terms its own followers would accept and give the strongest criticism beside it. Read the original works before you cite anyone, and check your own course's reading list. This is general information, not legal advice.

What is law?

Law is a rational ordering of human affairs for the common good. Human-made (positive) law is law in the full sense only if it fits a higher standard of reason or morality that people can discover, often called the natural law.

Law and morality

Tightly connected. Most versions say a seriously unjust rule lacks the full moral force of law. The classic slogan, from Augustine and Aquinas, is that an unjust law is a corruption of law rather than law.

Where does its authority come from?

Reason, human nature or God's order, depending on the thinker: the Stoics and Cicero (reason in nature), Aquinas (reason taking part in eternal law), Grotius (natural law valid even without God), Finnis (basic goods of human flourishing).

How should judges decide?

Citizens and judges may ask whether a rule respects basic justice, and in extreme cases a rule that violates fundamental rights may be refused effect. The post-war Radbruch formula in Germany is the best-known modern example.

The question it asks

Can an unjust rule really be law?

Main criticism

Critics say it blurs the difference between what the law is and what it ought to be, that people disagree about what morality requires, and that calling an unjust rule 'not law' makes it harder to describe unjust legal systems honestly.

Legacy today

Human rights law, the Nuremberg principles, the claim to unalienable rights in the American Declaration of Independence, and arguments about conscience and unjust laws.

Key thinkers

Aristotle, Cicero, Thomas Aquinas, Hugo Grotius, John Locke, Lon Fuller, John Finnis, Gustav Radbruch.

Aristotle (384–322 BC)
Marcus Tullius Cicero (106–43 BC)
Domitius Ulpianus (Ulpian) (c. 170–223 AD)
Gratian (active c. 1140)
Thomas Aquinas (1225–1274)
Hugo Grotius (1583–1645)
John Locke (1632–1704)
Sir William Blackstone (1723–1780)
Cesare Beccaria (1738–1794)
Lon L. Fuller (1902–1978)
John Finnis (born 1940)

Key works

Cicero, On the Laws
Aquinas, Summa Theologiae (Treatise on Law)
Grotius, On the Law of War and Peace (1625)
Fuller, The Morality of Law (1964)
Finnis, Natural Law and Natural Rights (1980)

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Read further

Stanford Encyclopedia of Philosophy: natural law theories. For the exact arguments, go to the original works above.

TheLawToKnow Tools’s guide to schools of legal thought is an educational overview. It is not legal advice. Report a mistake.