M. Tullius Cicero, De Officiis
Walter Miller, Ed.

[7] Since, therefore, the whole discussion is to be on the subject of duty, I should like at the outset to define what duty is, as, to my surprise, Panaetius has failed to do. For every systematic development of any subject ought to begin with a definition, so that everyone may understand what the discussion is about.

3. Every treatise on duty has two parts: one, ¹ dealing with the doctrine of the supreme good; the other, with the practical rules by which daily life in all its bearings may be regulated. The following questions are illustrative of the first part: whether all duties are absolute; whether one duty is more important than another; and so on. But as regards special duties for which positive rules are laid down, though they are affected by the doctrine of the supreme good, still the fact is not so obvious, because they seem rather to look to the regulation of everyday [p. 11] life; and it is these special duties that I propose to treat at length in the following books.