As Agamben (Opus Dei: An Archaeology of Duty) explains it, the shift from officium as status-specific behavior to something more like our conception of duty begins with the extension of officia to cover the human situation in general. This is already evident in the usage of Cicero and Seneca. In contrast to animals, human beings “conduct” (degere) and “govern” (gerere). The terms initially refer to the work of a governor, but even there attention is shifted from government specifically to “use of life” and “institution of life.”
At the root of this expansion of the idea of officium is the Stoic insight into human sociabilitas. As Seneca says, “I can lay down for humankind a rule, in short compass, for our duties in human relationships (humani officii); all that you behold, that which comprises both god and humanity, is one – we are the parts of one great body. Nature produced us related to one another, since she created us from the same source and to the same end. She engendered in us mutual affection, and made us prone to friendship.” Agamben glosses: “Officium thus constitutes the human condition itself, and human beings, insofar as they are membra . . . corporis magni . . . are beings of officium” (74-5).