Abstract
We have collective obligations precisely when (i) there exists a specific morally significant joint-necessity problem P such that agents a, b and c can collectively, but not individually, address P. Further, (ii) conscientious moral deliberation leads all of them (or a sufficiently large subset of them) to believe that some collectively available option O is morally optimal with regard to P. Finally, (iii) a, b and c (or a sufficiently large subset of them) must be in a position to determine individual (or joint) strategies to realise O and to achieve P.