The controversy between teleologists and deontologists, whether under these names or in other guises, is one of the long-standing disputes of ethics. In different branches of philosophy the perennial nature of a dispute may point to different things: in some, for example, it may properly incline one to say “a plague on both your houses” and thereafter to look for some way of disposing of the whole problem around which the philosophical problem has raged; in ethics, on the other hand, root-and-branch methods of excision are to be deplored, for here a perennial issue usually draws attention to points of view which have somehow to be reconciled if the problems underlying them are to be overcome. The deontology-teleology controversy seems to me a case in point. Here, if anywhere in ethics, a reconciliation must be effected; and in the present paper my primary aim is to induce deontologists and teleologists to abandon their mutual hostility.1I shall attempt to carry out this mission of philosophical good will through examining the ways in which we justify imperatives. In the first section of the paper I shall say something about the controversy itself, making it clear that I consider that it has roots which it would be inconvenient to expose at this stage of the inquiry; in the second I shall study the justification of a number of typical non-moral imperatives; in the third I shall apply the findings of the second to the justification of moral imperatives; and finally, in the fourth section I shall return to the deontology-teleology controversy and attempt to elucidate how it arises, to point out the two levels on which the same dispute (as it seems to me) can be found, and to suggest a way in which the essentials of the rival views may be accepted and combined.