On Duties

Cicero’s last work, written as a long letter of practical moral instruction to his son Marcus while the Roman republic was collapsing around him. Book one treats the honourable, organised under four virtues — wisdom, justice, greatness of spirit, and propriety — and includes his insistence that justice binds even in dealings with enemies and that promises and property rights are the foundation of social life. Book two treats the useful, arguing that reputation and influence are better won by service than by fear. Book three addresses the apparent conflicts between the two and denies there are real ones: what seems expedient but dishonourable never actually is. It was among the most widely read books in the West for the next eighteen centuries and a direct source for Renaissance humanism and for the American founders’ vocabulary of duty. Composed in Latin in 44 BC.

Why it’s on the list: McCord lists it in Pursuing the Good Life: Ethics and Personal Growth, next to his other Cicero entry and Marcus Aurelius’s “Meditations” — the section that supplies the classical practical ethics a builder is supposed to read before the modern moral theory that follows it.

Where I saw it: Brendan McCord’s Philosopher-Entrepreneur Reading List, in the Ethics, Morality, and Personal Growth part, section Pursuing the Good Life: Ethics and Personal Growth — a structured curriculum shared on X on March 9, 2026 and saved to Kyle’s Apple Note “Books To Read”. The full 211-entry transcription is on The Philosopher-Entrepreneur Reading List.

Connections

• Cicero — the author.
• Stoicism — the tradition Cicero is adapting here, largely from Panaetius.
• Moral Philosophy — the field the treatise belongs to; it was the standard Western textbook in it for centuries.
• Ethics — the practical discipline of book one’s four-virtue scheme.
• The Philosopher-Entrepreneur Reading List — the curriculum this came from.