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Natural law (the Stoics and Cicero)
classic statement c. 51 BC (Cicero); Stoic roots c. 300 BC· Idea or argument· Politics, society & justice
Mostly agreedGood evidence; some details uncertain.
The idea that a moral law built into nature, and knowable by reason, stands above any city's man-made laws.
See it on the Philosophy map →The idea
Idea: some things are right or wrong by nature, not by decree. The Stoics held that the universe is ordered by reason (logos), which every human shares, so all people are citizens of one world-city. Cicero gave the classic Latin statement around 51 BC: 'true law is right reason in agreement with nature,' the same in Rome and Athens. An unjust statute is not truly law. Main objection: whose 'nature'? Critics say it smuggles values into facts (see the is–ought gap).
Why it matters
It runs through Roman law, Aquinas, Locke's natural rights and the Declaration of Independence, and was invoked to support the Nuremberg trials' appeal to law above national statutes.
Where it comes from
Cicero's Republic (that passage survives only because Lactantius quoted it) and Laws; fragments of the early Stoics; Roman jurists such as Gaius and Ulpian on ius naturale.
Still debated
Whether nature really yields moral rules, and whose reason decides them, is still argued between natural-law theorists and legal positivists.
Connections (4)
▸Stoicism (founded by Zeno of Citium) first systematized Natural law (the Stoics and Cicero)Mostly agreed
The connection
The Stoics taught that one divine reason (logos) orders the cosmos and lives in every human mind. Living by nature therefore means living by reason, and that reason is a law binding everyone, everywhere. Cicero carried this into Latin and Roman legal thought as natural law (lex naturae).
When and how
Athens, with Zeno and Chrysippus (c. 300–206 BC); Rome, in Cicero's Republic and Laws (c. 54–51 BC).
How sure are we?
Fragments of Chrysippus call law 'king of all things', and Cicero openly credits Stoic sources.
Debates and open questions
Sophocles' Antigone and Aristotle had already contrasted natural and written justice, so whether the Stoics truly came first is debated.
▸Natural law (the Stoics and Cicero) was developed by Thomas AquinasWell documented
The connection
Aquinas took the Stoic and Ciceronian idea of a moral law built into nature and set it in a Christian scheme: eternal law in God's mind, natural law as humans' rational share in it, and human law, valid only if it agrees with natural law. Its first principle: do good and avoid evil.
When and how
The 'Treatise on Law' in the Summa Theologiae (Part I–II, questions 90–97), written around 1270, drawing on Cicero, Roman jurists and Augustine.
How we know
Aquinas cites Cicero, Roman law and Augustine by name in the treatise, and repeats Augustine's line that an unjust law seems to be no law at all.
Debates and open questions
Philosophers still debate whether natural law can be known by reason alone, without belief in God, and how it applies to modern rights.
▸Natural law (the Stoics and Cicero) grounded the rights theory of John LockeWell documented
The connection
The Stoics and Cicero taught that a law of right reason binds all people, above any ruler's decrees. Through Aquinas, Richard Hooker and Hugo Grotius, the tradition reached Locke, who used natural law to argue that people have rights to life, liberty and property before any government exists, and that governments must respect them.
When and how
Locke's Second Treatise of Government (1689), which leans on Hooker's Laws of Ecclesiastical Polity (1594); Cicero stated the idea in On the Republic around 51 BC.
How we know
Locke quotes Hooker repeatedly in the Second Treatise and frames his whole argument in natural law; his early Essays on the Law of Nature (c. 1663–64) survive.
Debates and open questions
Whether Locke's theory is traditional natural law or a modern, more individualist break with it, as Leo Strauss argued, is debated.
▸The is–ought gap challenges Natural law (the Stoics and Cicero)Mostly agreed
The connection
Natural law reasons from facts about human nature to moral rules: we are social creatures, so we ought to keep faith with others. Hume's gap says no 'ought' follows from 'is' facts alone without an added value premise. Critics use it to argue natural law hides its value assumptions.
When and how
Hume's Treatise of Human Nature, Book 3 (1740); later pressed by legal positivists and by G. E. Moore (1903).
How sure are we?
Hume states the gap explicitly; whether it defeats natural law is argued in print by Germain Grisez, John Finnis and their critics.
Debates and open questions
Natural-law theorists like Finnis reply that they never derive ought from is; whether that reply succeeds is still debated.