In het utilisme gaat het niet om vermeerderen van persoonlijk welzijn (nut, geluk) maar om het maatschappelijk welzijn. Dit veronderstelt dat op een of andere manier het welzijn of nut van verschillende individuen opgeteld kan worden tot maatschappelijk nut of welzijn. Bentham gaf al een beschrijving hoe dat volgens hem moet gebeuren. Het probleem van deze benadering is echter dat het niet duidelijk is hoe geluk in een (objectieve) maat kan worden uitgedrukt en kan worden opgeteld en afgetrokken.

Moderne vormen van utilisme gaan meestal niet uit van nut als geluksbeleving maar van nut als vervulling van verlangens of preferenties. Die opvatting is verwant aan de rationele keuzetheorie (en vergelijkbare theorieën als speltheorie en sociale keuzetheorie). Volgens die theorie is echter interpersonele nutsvergelijking niet mogelijk. Harsanyi meent echter dat de vaak genoemde bezwaren tegen interpersonele nutsvergelijking uiteindelijk geen hout snijden.

Een ander verschil tussen Bentham en Harsanyi is dat waar Bentham lijkt uit te gaan van het idee van het vergroten van het totale nut, Harsynai uitgaat van het gemiddelde nut. Meerdere utilisten hebben geworsteld met de vraag of het om gemiddeld nut of totaal nut gaat. Parfitt bijvoorbeeld laat zien dat als uitgegaan wordt van totaal nut dit leidt tot wat hij noemt de "repugnant conclusion": ten opzichte van een situatie met bijvoorbeeld 10 miljard mensen met een hogere levensstandaard kan altijd een situatie bedacht worden met een veel groter aantal mensen met een veel lagere levensstandaard waarbij het totale nut in de tweede situatie hoger is. Toch lijkt de eerste situatie moreel wenselijker dan de tweede. Dit lijkt een argument om uit te gaan van gemiddeld nut. Dat brengt echter weer andere paradoxale consequenties met zich mee. Zo zou gemiddeld nut betekenen dat het onwenselijk is om een kind voort te brengen dat waarschijnlijk minder dan gemiddeld nut of geluk ervaart. Ook zou het het wenselijk kunnen maken om dat groepen met een minder dan gemiddeld nut uitgeroeid worden omdat daarmee het gemiddeld nut stijgt.

Narveson meent in tegenstelling tot Parfitt dat het utilisme ook als uitgegaan wordt van het totale nut niet impliceert dat we de wereldbevolking moeten vergroten. Volgens hem berust de gedachte op een drogredenering. Je kan volgens hem niet zeggen dat een nieuw iemand (een pasgeboren kind) gelukkiger is dan eerder; dat is een onzinnige uitspraak en daarom mag je ook niet zeggen dat het totale geluk toeneemt door de geboorte van kinderen ook al zijn die kinderen gelukkig.

The interest of the community is one of the most general expressions that can occur in the phraseology of morals: no wonder that the meaning of it is often lost. When it has a meaning, it is this. The community is a fictitious body, composed of the individual persons who are considered as constituting as it were its members. The interest of the community then is, what?-the sum of the interests of the several members who compose it. (Bentham, An Introduction to the Principles of Morals and Legislation, Chapter 1)
IV. To a number of persons, with reference to each of whom to the value of a pleasure or a pain is considered, it will be greater or less, according to seven circumstances: to wit, the six preceding ones; viz.

1. Its intensity.
2. Its duration.
3. Its certainty or uncertainty.
4. Its propinquity or remoteness.
5. Its fecundity.
6. Its purity.
   And one other; to wit:
7. Its extent; that is, the number of persons to whom it extends; or (in other words) who are affected by it.

To take an exact account then of the general tendency of any act, by which the interests of a community are affected, proceed as follows. Begin with any one person of those whose interests seem most immediately to be affected by it: and take an account,

1. Of the value of each distinguishable pleasure which appears to be produced by it in the first instance.
2. Of the value of each pain which appears to be produced by it in the first instance.
3. Of the value of each pleasure which appears to be produced by it after the first. This constitutes the fecundity of the first pleasure and the impurity of the first pain.
4. Of the value of each pain which appears to be produced by it after the first. This constitutes the fecundity of the first pain, and the impurity of the first pleasure.
5. Sum up all the values of all the pleasures on the one side, and those of all the pains on the other. The balance, if it be on the side of pleasure, will give the good tendency of the act upon the whole, with respect to the interests of that individual person; if on the side of pain, the bad tendency of it upon the whole.
6. Take an account of the number of persons whose interests appear to be concerned; and repeat the above process with respect to each. Sum up the numbers expressive of the degrees of good tendency, which the act has, with respect to each individual, in regard to whom the tendency of it is good upon the whole: do this again with respect to each individual, in regard to whom the tendency of it is good upon the whole: do this again with respect to each individual, in regard to whom the tendency of it is bad upon the whole. Take the balance which if on the side of pleasure, will give the general good tendency of the act, with respect to the total number or community of individuals concerned; if on the side of pain,the general evil tendency, with respect to the same community.
   (Bentham, An Introduction to the Principles of Morals and Legislation, Chapter 4)

John C. Harsanyi

J.C. Harsanyi, "Morality and the theory of rational behaviour" in Sen, A. and Williams, B. (eds) (1982) Utilitarianism and Beyond, Cambridge: Cambridge University Press, pp. 50-52.

Simple reflection will show that the basic intellectual operation in […] interpersonal comparisons is imaginative empathy. We imagine ourselves to be in the shoes of another person, and ask ourselves the question, 'if I were now really in his position, and had his taste, his education, his social background, his cultural values, and his psychological make-up, then what would now be my preferences between various alternatives, and how much satisfaction or dissatisfaction would I derive from any given alternative?' (An 'alternative' here stands for a given bundle of economic commodities plus a given position with respect to various noneconomic variables, such as health, social status, job situation, family situation, etc.)

In other words, any interpersonal utility comparison is based on what I will call the similarity postulate, to be defined as the assumption that, once proper allowances have been made for the empirically given differences in taste, education, etc., between me and another person, then it is reasonable for me to assume that our basic psychological reactions to any given alternative will be otherwise much the same. Of course, it is only too easy to misapply this similarity postulate. For instance, I may fail to make proper allowances for differences in our tastes, and may try to judge the satisfaction that a devoted fish eater derives from eating fish in terms of my own intense dislike for any kind of sea food. Of course, sensible people will seldom make such an obvious mistake. But they may sometimes make much subtler mistakes of the same fundamental type.

In general, if we have enough information about a given person, and make a real effort to attain an imaginative empathy with him, we can probably make reasonably good estimates of the utilities and disutilities he would obtain from various alternatives. But if we have little information about him, our estimates may be quite wrong.

In any case, utilitarian theory does not involve the assumption that people are very good at making interpersonal utility comparisons. It involves only the assumption that, in many cases, people simply have to make such comparisons in order to make certain moral decisions -however badly they may make them. If I am trying to decide which member of my family is in greatest need of food, I may sometimes badly misjudge the situation. But I simply have to make some decision. I cannot let all members of my family go hungry because I have philosophical scruples about interpersonal comparisons and cannot make up my mind.

Nevertheless, interpersonal utility comparisons do pose important philosophical problems. In particular, they pose the problem that they require us to use what I have called the similarity postulate. Yet this postulate, by its very nature, is not open to any direct empirical test. I may very well assume that different people will have similar psychological feelings about any given situation, once differences in their tastes, educations, etc. have been allowed for. But I can never verify this assumption by direct observation since I have no direct access to their inner feelings.

Therefore, the similarity postulate must be classified as a nonempirical a priori postulate. But, of course, interpersonal utility comparisons are by no means unique among empirical hypotheses in their dependence on such nonempirical postulates. In actual fact, whenever we choose among alternative empirical hypotheses, we are always dependent on some nonempirical choice criteria. This is so because the empirical facts are always consistent with infinitely many alternative hypotheses, and the only way we can choose among them is by using a priori nonempirical choice criteria, such as simplicity, parsimony, preference for the 'least arbitrary' hypothesis, etc.

Our similarity postulate is a nonempirical postulate of the same general type. Its intuitive justification is that, if two individuals show exactly identical behaviour -or, if they show different behaviour but these differences in their observable behaviour have been properly allowed for - then it will be a completely arbitrary and unwarranted assumption to postulate some further hidden and unobservable differences in their psychological feelings.
We use this similarity postulate not only in making interpersonal utility comparisons but also in assigning other people human feelings and conscious experiences at all. From a purely empirical point of view, a world in which I would be the only person with real conscious experiences while all other people were mindless robots would be completely indistinguishable from our actual world where all individuals with human bodies are conscious human beings. (Indeed, even a world in which I alone would exist, and all other people as well as the whole physical universe would be merely my own dream -solipsism -would be empirically indistinguishable from the world we actually live in.) When we choose the assumption that we actually live in a world populated by millions of other human beings, just as real and just as conscious as we are ourselves, then we are relying on the same similarity postulate. We are essentially saying that, given the great basic similarity among different human beings, it would be absurd to postulate fundamental hidden differences between them by making one person a conscious human being while making the others mere robots, or by making one person real while making the others mere dream figures. (Strictly speaking, we cannot exclude the possibility that somebody who looks human will turn out to be an unfeeling robot; but we have no scientific or moral justification to treat him like a robot before the evidence for his being a robot becomes overwhelming.)

There is no logical justification for using the similarity postulate to reject the hypothesis that other people are mere robots (or mere dream figures) yet to resist interpersonal utility comparisons based on the very same similarity postulate. It is simply illogical to admit that other people do have feelings and, therefore, do derive some satisfaction from a good meal in the same way we do; yet to resist the quantitative hypothesis that the amount of satisfaction they actually obtain from a good dinner -that is, the personal importance they attach to a good dinner -must be much the same as it is in our own case, after proper allowances have been made for differences in our tastes, in the food requirements of our bodies, in our state of health, etc. A willingness to make interpersonal comparisons is no more than an admission that other people are just as real as we are, that they share a common humanity with us, and that they have the same basic capacity for satisfaction and for dissatisfaction, in spite of the undeniable individual differences that exist between us in specific detail.

The long-standing opposition by many philosophers and social scientists to interpersonal utility comparisons goes back to the early days of logical positivism, when the role of nonempirical a priori principles, like the similarity postulate, in a choice among alternative empirical hypotheses was very poorly understood. We owe an immense intellectual debt to the logical positivists for their persistent efforts to put philosophy on truly scientific foundations by combining strict empiricism with the strict mathematical rigour of modern logic. But there is no denying that many of their specific philosophical views were badly mistaken, and that they had little appreciation in their early period for the importance of a priori principles and, more generally, for the importance of theoretical ideas in empirical science.

Derek Parfitt

Derek Parfit "Overpoulation and the Quality of Life", in Glover, J. (ed.) (1990) Utilitarianism and Its Critics, New York: Macmillan., 136-138.

Best of all would be Z. This is an enormous population all of whom have lives that are not much above the level where they would cease to be worth living. A life could be like this either because its ecstasies make its agonies seem just worth enduring, or because it is painless but drab. Let us imagine lives in Z to be of this second kind. There is nothing bad in each of these lives; but there is little happiness, and little else that is good. The people in Z never suffer; but all they have is muzak and potatoes. Though there is little happiness in each life in Z, because there are so many of these lives Z is the outcome in which there would be the greatest total sum of happiness. Similarly, Z is the outcome in which there would be the greatest quantity of whatever makes life worth living. (The greatest mass of milk might be in a vast heap of bottles each containing only one drop.)

It is worth comparing Z with Nozick's imagined Utility Monster. This is someone who would gain more happiness than we would lose whenever he is given any of our resources. Some Utilitarians believe that the Hedonistic Total Principle should be our only moral principle. Nozick claims that, on this Utilitarian theory, it would be best if all our resources were taken away and given to his Utility Monster, since this would produce the greatest total sum of happiness. As he writes, "unacceptably, the theory seems to require that we all be sacrificed in the monster's maw."

How could it be true that, if all mankind's resources were given to Nozick's Monster, this would produce the greatest total sum happiness? For this to be true, this Monster's life must, compared with other people's lives, be millions of times as much worth living. We cannot imagine, even in the dimmest way, what such a life would be like. Nozick’s appeal to his Monster is therefore not a good objection to the Total Principle. We cannot test a moral principle by applying it to a case which we cannot even imagine.
Return now to the population in outcome Z. This is another Utility Monster. The difference is that the greater sum of happiness would come from a vast increase, not in the quality of one person's life, but in the number of lives lived. And this Utility Monster can be imagined. We can imagine what it would be for someone's life to be barely worth living -containing only muzak and potatoes. And we can imagine what it would be for there to be many people with such lives. In order to imagine Z, we merely have to imagine that there would be very many.

We could not in practice face a choice between A and Z. Given the limits to the world's resources, we could not in fact produce the greatest possible sum of happiness, or the greatest amount of whatever makes life worth living, by producing an enormous population whose lives were barely worth living. But this would be merely technically impossible. In order to suppose it possible, we merely need to add some assumptions about the nature and availability of resources. We can therefore test our moral principles by applying them to A and Z.

The Total Principle implies that Z would be better than A. More generally, the principle implies.

The Repugnant Conclusion: Compared with the existence of very many people-say, ten billion-all of whom have a very high quality of life, there must be some much larger number of people whose existence, if other things are equal, would be better, even though these people would have lives that are barely worth living.

As its name suggests, most of us find this conclusion hard to accept. Most of us believe that Z would be much worse than A. To keep this belief, we must reject the Total Principle. We must also reject the broader view that any loss in the quality of life could be outweighed by a sufficient increase in the total quantity of whatever makes life worth living. Unless we reject this view, we cannot avoid the Repugnant Conclusion.

Jan Narveson

J. Narveson, "Utilitarianism and New Generations", Mind, 1967.

One of the stock objections to utilitarianism goes like this: “If utilitarianism is correct, then we must be obliged to produce as many children as possible, so long as their happiness would exceed their misery.” It has always seemed to me that there is a certain air of sophistry about this argument, and in this paper, I shall endeavor to demonstrate this by exposing the fallacies upon which it is founded.

In order to show that the general happiness would be increased by our having a child, the argument would have to go as follows. Imagine that the number of people is N, and that the total happiness is H, the average happiness therefore being N/H = 1. Now suppose that we have good evidence that any child produced by us would be twice as happy as that, giving him a value of 2. Then the average happiness after he is born will be (N+2)/(H+1), which would be somewhat larger, therefore, than before. Does this give us a moral reason to produce children? No. We have committed a fallacy.

[…]

The argument that an increase in the general happiness will result from our having a happy child involves precisely the same fallacy. If you ask, "Whose happiness has been increased as a result of his being born?" the answer is that nobody's has. Of course, his being born might have indirect effects on the general happiness, but that is quite another matter. The "general populace" is just as happy as it was before; now, what of our new personnel? Remember that the question we must ask about him is not whether he is happy, but whether he is happier as a result of being born. And if put this way, we see that again we have a piece of nonsense on our hands if we suppose that the answer is either "yes" or "no." For if it is, then with whom, or with what, are we comparing his new state of bliss? Is the child, perhaps, happier than he used to be before he was born? Or happier, perhaps, than his alter ego? Obviously, there can be no sensible answer here. The child cannot be happier as a result of being born, since we would then have a relative term lacking on relatum. The child's happiness has not been increased, in any intelligible sense, as a result of his being born; and since nobody else's has either, directly; there is no moral reason for bringing him into existence.