attention to a very limited class of actions, which have been selected because they are those which most commonly occur to mankind as possible alternatives. With regard to these they may possibly have shewn that one alternative is better, i.e. produces a greater total of value, than others. But it seems desirable to insist, that though they have represented this result as a determination of duties, it can never really have been so. For the term duty is certainly so used that, if we are subsequently persuaded that any possible action would have produced more good than the one we adopted, we admit that we failed to do our duty. It will, however, be a useful task if Ethics can determine which among alternatives likely to occur will produce the greatest total value. For, though this alternative cannot be proved to be the best possible, yet it may be better than any course of action which we should otherwise adopt.
92. A difficulty in distinguishing this task, which Ethics may perhaps undertake with some hope of success, from the hopeless task of finding duties, arises from an ambiguity in the use of the term ‘possible.’ An action may, in one perfectly legitimate sense, be said to be ‘impossible’ solely because the idea of doing it does not occur to us. In this sense, then, the alternatives which do actually occur to a man would be the only possible alternatives; and the best of these would be the best possible action under the circumstances, and hence would conform to our definition of ‘duty.’ But when we talk of the best possible action as our duty, we mean by the term any action which no other known circumstance would prevent, provided the idea of it occurred to us. And this use of the term is in accordance with popular usage. For we admit that a man may fail to do his duty, through neglecting to think of what he might have done. Since, therefore, we say that he might have done, what nevertheless did not occur to him, it is plain that we do not limit his possible actions to those of which he thinks. It might be urged, with more plausibility, that we mean by a man’s duty only the best of those actions of which he might have thought. And it is true that we do not blame any man very severely for omitting an action of
