De Legibus (On the Laws)

De Legibus is Cicero’s dialogue On the Laws (c. 52 BC), the companion to De Re Publica. Where the Republic preserves the famous definition of true law, De Legibus gives the argument, and it is the most developed statement of natural law to survive from antiquity.

The Argument of Book I

Speaking in the dialogue, Marcus (Cicero) insists that law must be understood not from “the praetor’s edict” or “the Twelve Tables” but “in the sublimest doctrines of philosophy.” His thesis is that law and justice are grounded in nature, not convention:

• Reason is “the common property of God and man,” and “this right reason is what we call Law.” Because reason is shared, gods and men form “one immeasurable Commonwealth,” and law is the same for all.
• Therefore “man is born for justice, and that law and equity are not a mere establishment of opinion, but an institution of nature.” Cicero explicitly condemns the view “that all things are necessarily just, which are established by the civil laws and the institutions of the people” — utility cannot be the measure of justice, for “nature herself is the foundation of justice.”
• “Law, which is nothing else than right reason enjoining what is good, and forbidding what is evil,” precedes any written statute; an unjust enactment is not truly law at all.

Book I grounds justice in nature and human fellowship; Books II and III apply the principle to religious law and to the magistracies of the ideal commonwealth.

Why It Completes the Cicero Entry

De Re Publica gave the tradition its slogan; De Legibus gives it the reasoned case that later natural-law thinkers expand. The claim that an unjust law fails to be law passes to Aquinas (lex iniusta non est lex); the grounding of law in a shared human nature accessible to reason passes to Grotius and Locke. This article closes the De Legibus gap noted when De Re Publica was first compiled.

See Also

• Cicero - author reference
• De Re Publica - the companion dialogue, source of the famous definition
• Natural Law and Natural Order - the tradition this dialogue most fully argues
• Treatise on Law - the medieval synthesis carrying Cicero’s “unjust law is no law” forward

Sources

• Cicero, De Legibus (Full Text) - Book I (law and justice from nature and right reason); Barham translation via ToposText