Some people say that you can’t make interpersonal comparisons of utility. You can’t, in other words, say that Anne gets more utility from a piece of chocolate than Bill, or that Claire gets more disutility from a punch in the face than David. Everyone has their own scales of utility (based on an ordinal ranking of things) and those scales do not transfer between people. This means that the only thing you can say is that Bill gets more utility from a piece of chocolate than what Bill gets from an apple (at least at a certain point in time), and this can be proven by, for example, examining how much he is willing to pay for chocolate or apples.
To assess whether this is a good objection to utilitarianism we first have to establish what is meant by “utility”. Jeremy Bentham was quite clear about what he meant: utility is basically the same as usefulness (and when people in general say “utilitarian” the usually mean “useful for practical purposes”). Then, of course, we have to ask: useful for what? Bentham’s answer is, of course, pleasure. A law or an action has high utility if it contributes to maximizing pleasure.
If “utility” is interpreted in this way, there is no problem (at least in principle) of interpersonal comparisons. What we are interested in is actually pleasure, and not utility in itself. And if we can make interpersonal comparisons of pleasure and pain (and I can’t see how anyone can deny this, because that would be the same as denying that human beings can have meaningful social interactions with each other), then we can also discuss meaningfully which actions or laws have more or less utility.
However, when people (often economists) say that you cannot make interpersonal comparisons of utility they have another conception of utility in mind. By utility, they usually mean something like “degree of satisfaction”. And I would agree that you cannot really compare degrees of satisfaction between different individuals, because that is really a mystical concept. How much sense does it really make to say “Wow, I feel so satisfied”, without connecting this feeling to something more tangible – and morally relevant – like pleasure? (Just try to satisfy someone sexually without giving them pleasure…)
Still, economists thought that they were becoming more “scientific” when they, during the second half of the 19th century, switched from pleasure to utility as the thing that should be studied and maximized. But this made economics less relevant for politics, because isn’t pleasure (happiness) what we want politics to bring, rather than maximization of “utility”?
Furthermore, “economic” preference-utilitarianism seems to disregard wishes that cannot be “revealed” or “demonstrated” by monetary transactions (or perhaps by barter). It seems rather strange that we can only say that a person’s preferences (or scales of utility) is revealed by how she has in fact (ex post facto) spent her money or managed her resources. This would mean that a very poor person cannot have the preference of owning a fancy car and a big house, and that he would get very much “utility” from those things, because we have not observed that he has spent any many to acquire those things. His actions seem to reveal that he “prefers” (gets the most utility from) having a hard, low-paid job instead of choosing the career that would get him a fancy car and a big house.
Thus, to make sense, preference-utilitarianism has to take account of imagined preferences, as well as revealed or demonstrated ones. Otherwise it has no relevance for the real world and people’s real wishes and aspirations. But then we all know that wishing for some things does not guarantee that you will be happier once you get what you wish for. On the contrary, many studies have shown that people who suddenly win a lot of money may get happier for a short while, but that they quickly return to the same (or lower) happiness levels as before their lucky break. Again, “utility”, perceived as preference-satisfaction, has no meaning when it is not connected to maximization of pleasure (and minimization of pain).
Anyway, when you hear someone complain against utilitarianism by claiming that you can’t make interpersonal comparisons of utility, you can just relax and reply that you are not a preference-utilitarian, but a hedonistic utilitarian; and we hedonists are not concerned about comparing and maximizing utility, but pleasure. So if your antagonists want to continue this line of criticism they would have to deny that we can make interpersonal comparisons of pleasure and pain. They must deny that we can, for example, say that Anne gets more pain from being burnt at the stake than what Bill gets from the prick of a needle on his finger.
Of course, one can deny that such comparisons can be made, and claim that we humans are inscrutable mysteries to each others, and that we can’t make any – not even rough and imprecise – general statements about what goes on in most people’s brains and nervous systems. But I suspect that only a philosophical curmudgeon would make such a claim. A more reasonable objection would be to claim that we can make interpersonal comparisons of pleasure and pain, but that they are too imprecise to count as scientific. Then I would just reply that ethics cannot be a precise science, just as the art of living a good life cannot be a precise scientific endeavor.