Utilitarians—as well as moral philosophers who have not been utilitarians—have not always failed to notice the fact that we think actions are right if they are of a sort which would produce good consequences if generally practised, or are wrong if they are of a sort which would produce bad consequences if other people did the same. Mill, for example, remarked: "In the case of abstinences—indeed of things which people forbear to do from moral considerations, though the consequences in the particular case might be beneficial—it would be unworthy of an intelligent agent not to be consciously aware that the action is of a class which, if practised generally, would be generally injurious, and that this is the ground of the obligation to abstain from it." But utilitarians have not always realised that, in admitting that the performance of such actions is a duty, they are departing from, or, at least, modifying, utilitarianism as it is stated above. And that they are departing from, or modifying, utilitarianism, as it is usually thought of, is clear. For actions which are permissible, according to utilitarianism as I have defined it above, might well not be permissible, according to utilitarianism in this modified form. For it may very well be true of an action, both that there is no other action within the power of the agent that would produce better consequences than it, and that it is an instance of a class of actions which would produce harmful consequences if they were to be generally performed. In this case, I should, according to utilitarianism as it is normally thought of, be acting rightly if I performed it; whereas, according to this modified form of utilitarianism, I should be acting wrongly.
(J. Harrison, "Utilitarianism, Universalisation, and Our Duty to Be Just," Proceedings of the Aristotelian Society, n.s., 53 [1952-1953]: 105-34, at 113 [footnote omitted])
Note from KBJ: Here is an example. Suppose I am shipwrecked with my grandfather on a deserted island. Before he dies, he asks me to promise him that I will bury his body. I make the promise. According to act utilitarianism, I should break the promise, since keeping it will (1) do no good and (2) do some bad. (It's hard work digging a grave.) According to rule utilitarianism, I should keep the promise, since breaking it "is an instance of a class of actions which would produce harmful consequences if they were to be generally performed." This example shows that act utilitarianism and rule utilitarianism are distinct theories. It does not tell us which theory is best or preferable. Some people prefer act utilitarianism; some prefer rule utilitarianism. Some people reject both theories.
