Ethics, therefore, is quite unable to give us a list of duties: but there still remains a humbler task which may be possible for Practical Ethics. Although we cannot hope to discover which, in a given situation, is the best of all possible alternative actions, there may be some possibility of showing which among the alternatives, likely to occur to anyone, will produce the greatest sum of good. This second task is certainly all that Ethics can ever have accomplished: and it is certainly all that it has ever collected materials for proving; since no one has ever attempted to exhaust the possible alternative actions in any particular case. Ethical philosophers have in fact confined their 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 shown 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 which, as we say, “he could not be expected to think.” But even here it is plain that we recognise a distinction between what he might have done and what he might have thought of doing: we regard it as a pity that he did not do otherwise. And “duty” is certainly used in such a sense, that it would be a contradiction in terms to say it was a pity that a man did his duty.
We must, therefore, distinguish a possible action from an action of which it is possible to think. By the former we mean an action which no known cause would prevent, provided the idea of it occurred to us: and that one among such actions, which will produce the greatest total good, is what we mean by duty. Ethics certainly cannot hope to discover what kind of action is always our duty in this sense. It may, however, hope to decide which among one or two such possible actions is the best: and those which it has chosen to consider are, as a matter of fact, the most important of those with regard to which men deliberate whether they shall or shall not do them. A decision with regard to these may therefore be easily confounded with a decision with regard to which is the best possible action. But it is to be noted that even though we limit ourselves to considering which is the better among alternatives likely to be thought of, the fact that these alternatives might be thought of is not included in what we mean
