On Duties (De Officiis)

Cicero's last philosophical work, written in late 44 BCE, in the months after the assassination of Julius Caesar, as a letter in three books to his son Marcus, then studying in Athens. Drawing on the Stoic Panaetius, it asks how a person should act in public and private life. Book I treats what is honourable through the four cardinal virtues: wisdom; justice, which forbids harming others and requires good faith and generosity; greatness of spirit; and propriety, the fitting conduct that suits our shared human nature and our individual roles. Book II treats what is beneficial, such as winning goodwill and glory honestly. Book III takes up apparent conflicts between the honourable and the beneficial and argues that they are never real: what is wrong cannot be truly useful. Its test cases include a grain merchant who knows more supplies are coming during a famine, the ring of Gyges, and Regulus returning to Carthage to keep his oath.

It was among the most widely read works of ethics in Europe for centuries, and its cases on honesty in business and public office still make good arguments.