Duty (from "due," that which is owing, O. Fr. deu, did, past participle of devoir; Lat. debere, debitum; cf. "debt") is a term that conveys a sense of moral commitment to someone or something. The moral commitment is the sort that results in action, and it is not a matter of passive feeling or mere recognition. When someone recognizes a duty, that person commits himself/herself to the cause involved without considering the self-interested courses of actions that may have been relevant previously. This is not to suggest that living a life of duty precludes one from the best sort of life, but duty does involve some sacrifice of immediate self-interest.
Cicero is an early philosopher who acknowledged this possibility. He discusses duty in his work “On Duty." He suggests that duties can come from four different sources:
From the root idea of obligation to serve or give something in return, involved in the conception of duty, have sprung various derivative uses of the word; thus it is used of the services performed by a minister of a church, by a soldier, or by any employee or servant.
Many schools of thought have debated the idea of duty. While many assert mankind's duty on their own terms, some philosophers have absolutely rejected a sense of duty.