On Duties

Chapter-by-chapter summary

Part 1: A Father's Letter to a Distant Son (Book 1, opening)

Late in 44 BC, with Caesar dead and the republic in turmoil, Cicero had been pushed out of real power. His son Marcus was studying philosophy in Athens, so Cicero wrote him a long, fatherly guide to living well. He says he follows the Greek Stoic Panaetius, but he adapts him freely for Roman life. Cicero also separates two levels of duty: the “perfect” duty only a wise person could fulfil, and the “ordinary” duty that decent people can manage. This split matters because it makes the book usable by everyone, not just by saints.

Part 2: The Four Sources of Goodness (Book 1, wisdom and justice)

Cicero says every duty grows from four parts of moral goodness: wisdom, justice, courage and self-control. On wisdom, he praises the search for truth but warns against rushing to conclusions or wasting time on puzzles that help no one. Justice is the heart of the book. He names two kinds of injustice: harming others, and watching harm happen when you could stop it. Keeping promises and respecting property belong here too. He repeats a line he credits to Plato, that we are not born for ourselves alone. Duty starts with the fact that we live among other people.

Part 3: Courage, Fitting Behaviour and Roles (Book 1, second half)

Courage, for Cicero, covers more than battle. It also means standing up to injustice in public life. But courage without justice is just violence, and courage chasing fame is not the real thing. Next he turns to propriety, acting in a way that fits. We each play four roles at once: a reasoning human being, a person with our own temperament, someone in particular circumstances, and someone who has chosen a path in life. He advises against copying others at the cost of your own nature. Finally he ranks our duties: country first, then parents, then children and household, then relatives and friends. Duty, he shows, depends on relationships, and the strongest claims come first.

Part 4: What Is Truly Useful? (Book 2)

Book 2 asks what is truly useful. Cicero's answer is surprisingly human: the most useful thing in life is other people's cooperation, and that comes from trust, respect and goodwill. Rulers who govern through fear, he warns, live in fear themselves. He is hard on politicians who cancel debts or hand out land to win popularity. On generosity, he prefers help given through effort and time over cash, and he says not to give so much that you ruin yourself or your family. The lesson is that reputation and influence grow slowly, from honest and caring acts.

Part 5: When Right and Useful Seem to Clash (Book 3, opening)

Book 3 takes on the hardest question: what if the right thing and the profitable thing seem to clash? Cicero notes that Panaetius never wrote this part, so he builds it himself. His starting point is that a wrong act can never truly be useful; the clash is an illusion created by short-term thinking. To test this he uses the story of the ring of Gyges, a ring that makes its wearer invisible. If you could do wrong and never be found out, would you? Cicero says a good person would not, because goodness does not depend on being watched. The test separates real character from reputation.

Part 6: Hard Cases from Business and Daily Life (Book 3, middle)

Cicero then tests his idea on business cases. In the best known, a grain merchant from Alexandria reaches a starving Rhodes and knows that more ships are close behind. Should he say so, or sell high? Two Stoic teachers disagree. Diogenes of Babylon allows silence if no law is broken. Antipater of Tarsus says a seller must share what he knows for the good of everyone. Cicero sides with Antipater. He adds other examples, such as selling a house with a hidden flaw. His point is that what the law permits and what a decent person does are different things.

Part 7: Promises, Oaths and Regulus (Book 3, ending)

The last theme is promises and oaths. Cicero's model is Regulus, a Roman general captured by Carthage in the First Punic War. According to tradition, Carthage sent him to Rome on oath to return if no prisoner exchange was agreed. In the Senate he argued against the exchange, then went back to Carthage as he had sworn, and was reportedly put to a cruel death. Cicero does not call this a bad bargain. He treats it as proof that keeping faith outweighs personal suffering. He closes by telling Marcus that nothing contrary to virtue can ever be a real benefit.

Key people and terms

• Cicero (106–43 BC): Roman lawyer, orator and consul in 63 BC. Pushed out of power by Caesar and later hunted by Mark Antony, he wrote On Duties in his final year. He was killed in December 43 BC.
• Marcus Cicero: Cicero's son and the person the book is addressed to. He was studying in Athens under the philosopher Cratippus when his father wrote, so the whole book reads like a long letter of advice.
• Panaetius: A Stoic philosopher from Rhodes in the second century BC. His work on appropriate acts is the main model for Books 1 and 2, though Cicero rewrites it for Roman readers and fills the gap in Book 3.
• Diogenes of Babylon and Antipater of Tarsus: Two Stoic teachers whose argument about the Rhodes grain merchant drives a key part of Book 3. Diogenes tolerates silence if the law is kept; Antipater demands full disclosure. Cicero backs Antipater.
• Regulus: Marcus Atilius Regulus, a Roman general in the First Punic War. Cicero holds him up as the model of someone who kept an oath at terrible personal cost, and as proof that keeping your word can matter more than staying safe.
• Honestum: Latin for what is morally right and admirable. It is the book's central standard: an act is a duty if it fits the four virtues of wisdom, justice, courage and self-control.
• Utile: Latin for the useful or advantageous. Books 2 and 3 ask whether it can ever pull against honestum, and Cicero's firm answer is no, because real advantage always includes trust and good standing.

Applying On Duties in real life

This book works best when you test it on choices you actually face. Here are questions the text raises:

• When a shortcut would pay off but involves hiding something, could you do it openly? Cicero treats the urge to hide as a warning.
• Is there someone you could protect or help and are choosing to ignore? That, for Cicero, is the second kind of injustice.
• Which of your roles (student, child, friend, team member) is making a claim on you right now, and which claim is strongest?
• Are you treating “it is not against the rules” as the same as “it is fine”?

If you are writing about the book for school or a discussion group, pick one of Cicero's claims, such as “the useful and the right never conflict”, and test it against a modern case: a sports team, an online shop, a group chat. Say whether you agree and why. Take the best objection seriously too: can a person really lose out and still say they chose well? Finish by saying what you would do. The question is ancient, but it has not changed.