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Wellsprings
ethics

Duty

καθῆκον / officium

The 'fitting' action that reason calls for in each moment — the Stoic and Ciceronian root of the very idea of duty.

Duty, or kathēkon in Greek and officium in Latin, refers to actions that are appropriate or incumbent upon a person given their nature and circumstances. The Stoics, beginning with Zeno the school's founder, developed this concept as central to their ethics. A kathēkon is an action aligned with reason and one's role in the natural order—neither inherently virtuous nor vicious, but the proper thing to do in a given situation. Cicero adopted and expanded the Roman version, officium, making it foundational to practical morality.

The Stoics distinguished between unconditional duties that apply universally and conditional ones shaped by particular relationships and social roles. A person's duty flows from their position: a parent must care for children, a citizen must serve the state, a friend must show loyalty. By understanding these relational duties and aligning your will with nature's rational order, you discover what you must do. This framework allowed ancient philosophers to navigate ethical life not through abstract rules alone but through recognition of the concrete obligations arising from who and where you are.

Where this idea shows up

340 Greek sources

Where to read it