(4) A fourth conclusion, which follows from the fact that what is right or what is our duty must in any case be defined as what is a means to good, is, as was pointed out above (§ 89), that the common distinction between these and the expedient or useful, disappears. Our duty is merely that which will be a means to the best possible, and the expedient, if it is really expedient, must be just the same. We cannot distinguish them by saying that the former is something which we ought to do, whereas of the latter we cannot say we ought. In short the two concepts are not, as is commonly assumed by all except Utilitarian moralists, simple concepts ultimately distinct. There is no such distinction in Ethics. The only fundamental distinction is between what is good in itself and what is good as a means, the latter of which implies the former. But it has been shewn that the distinction between duty and expediency does not correspond to this: both must be defined as means to good, though both may also be ends in themselves. The question remains, then: What is the distinction between duty and expediency? (§ 101 ¶ 1)

One distinction to which these distinct words refer is plain enough. Certain classes of action commonly excite the specifically moral sentiments, whereas other classes do not. And the word duty is commonly applied only to the class of actions which excite moral approval, or of which the omission excites moral disapproval—especially to the latter. Why this moral sentiment should have become attached to some kinds of actions and not to others is a question which certainly not yet be answered; but it may be observed that we have no reason to think that the actions to which it was attached were or are, in all cases, such as aided or aid the survival of a race: it was probably originally attached to many religious rites and ceremonies which had not the smallest utility in this respect. It appears, however, that, among us, the classes of action to which it is attached also have two other characteristics in enough cases to have influenced the meaning of the words duty and expediency. One of these is that duties are, in general, actions which a considerable number of individuals are strongly tempted to omit. The second is that the omission of duty generally entails consequences markedly disagreeable to some one else. The first of these is a more univeral characteristic than the second: since the disagreeable effects on other people of the self-regarding duties, prudence and temperance, are not so marked as those on the future of the agent himself; whereas the temptations to imprudence and intemperance are very strong. Still, on the whole, the class of actions called duties exhibit both characteristics: they are not only actions, against the performance of which there are strong natural inclinations, but also actions of which the most obvious effects, commonly considered goods, are effects on other people. Expedient actions, on the other hand, are actions to which strong natural inclinations prompt us almost universally, and of which all the most obvious effects, commonly considered good, are effects upon the agent. We may then roughly distinguish duties from expedient actions, as actions with regard to which there is a moral sentiment, which we are often tempted to omit, and of which the most obvious effects are effects upon others than the agent. (§ 101 ¶ 2)

But it is to be noticed that none of these characteristics, by which a duty is distinguished from an expedient action, gives us any reason to infer that the former class of actions are more useful than the latter—that they tend to produce a greater balance of good. Nor, when we ask the question, Is this my duty? do we mean to ask whether the action in question has these characteristics: we are asking simply whether it will produce the best possible result on the whole. And if we asked this question with regard to expedient actions, we should quite as often have to answer it in the affirmative as when we ask it with regard to actions which have the three characteristics of duties. It is true that when we ask the question, Is this expedient? we are making a different question—namely, whether it will have certain kinds of effect, with regard to which we do not enquire whether they are good or not. Nevertheless, if it should be doubted in any particular case whether these effects were good, this doubt is understood as throwing doubt upon the action’s expediency: if we are required to prove an action’s expediency, we can only do so by asking precisely the same question by which we should prove it a duty—namely, Has it the best possible effects on the whole? (§ 101 ¶ 3)

Accordingly the question whether an action is a duty or merely expedient, is one which has no bearing on the ethical question whether we ought to do it. In the sense in which either duty or expediency are taken as ultimate reasons for doing an action, they are taken in exactly the same sense: if I ask whether an action is really my duty or really expedient, the predicate of which I question the applicability to the action in question is precisely the same. In both cases I am asking, Is this event the best on the whole that I can effect?; and whether the event in question be some effect upon what is mine (as it usually is, where we talk of expediency) or some other event (as is usual, where we talk of duty), this distinction has no more relevance to my answer than the distinction between two different effects on me or two different effects on others. The true distinction between duties and expedient actions is not that the former are actions which it is in any sense more useful or obligatory or better to perform, but that they are actions which it is more useful to praise and to enforce by sanctions, since they are actions which there is a temptation to omit. (§ 101 ¶ 4)