Utilitarianism is fundamentally about rationalizing human behavior; this is its first goal before arriving at its stated goal. We see this in Bentham as well as Sidgwick; a desire to do away with the contingency in human decisionmaking by optimizing to a single specified end; be it happiness or utility broadly defined. In fact the particulars of the end do not matter, as Martha Nussbaum explains in The Fragility of Goodness; all that matters is that every human choice is put into the same value scale so that making the right choice boils down to a simple matter of calculation. There is a great deal that is unsatisfying about this approach, and to my mind a good example of where it isn’t very useful is in explaining the phenomenon of dog ownership or pet ownership in general.

The commensurability problem can be traced back at least to the ancient Greeks. In the Platonic dialogue Protagoras, Socrates argues that it is absurd to assert that one would ever think X is more valuable than Y but then choose Y anyway. Nussbaum fleshes this out by presenting two scenarios: if we consider a case where someone considers good health more valuable than eating donuts, but the donuts right in front of us, right now, is so tempting that we eat it, Socrates’ assertion seems irrelevant and strange. If, however, someone has a choice between taking $50 and $100 and chooses the $50, it does indeed seem absurd and we wouldn’t expect it to happen. Socrates — at least, the Socrates of Protagoras — believes that rationality should reduce all human decisions to commensurable choices just like the latter scenario.

How one understands dog ownership from this perspective is a mystery to me. If you own a dog and take the trouble to keep it alive, healthy, and happy, you have to sacrifice a great deal. There are the simple financial realities of feeding a dog and vet visits and medication or treatment when necessary, and often dog walkers as well. Then there is the sacrificed freedom — it is much harder to be spontaneous after work in terms of going out or seeing people; someone has to make sure to dog goes out, gets fed, and so on. And, for many people, there’s the added anxiety of having a life that depends on you — you invest emotions in your dog in a way that makes you vulnerable.

It’s hard to imagine a world of commensurable values where this arrangement makes sense. If you get $10,000 of value from owning a dog, wouldn’t it be easier to just seek out $10,000 of value through going out to restaurants, or watching more movies, or any number of other ways that is less expensive financially and emotionally? Commensurability is fundamentally about interchangeability; the high cost value of dog ownership should, in this world, have available substitutes.

To my mind there are three responses possible from the utilitarian camp. The first is Socrates’ — yes, dog ownership is irrational, at least as it is done today. The healing hand of philosophy should cure us of this irrationality. The second is Benthamite and especially Paretian — people’s de facto preferences are simply rationalized as utility maximizing. The third is a pessimistic version of the first — it is irrational, but it’s an incurable irrationality, and in this case a mostly harmless one. But other, similar irrationalities need to be managed via nudging or straightforward coercion for people’s own good.

The second answer is not very satisfying. It has been put to good use in economics for system-wide discussions but it seems to me that if you’re going to rationalize everything that people actually choose, you haven’t got much of a philosophy of ethics.

The first answer is not very plausible, for reasons given in the third answer. Human beings simply do not work this way. Moreover, if there were humans that worked this way, we would find them repellent. Loved ones are easily substituted for and nothing holds a special value to us. It is a world without dignity.

To the third answer we must say — what reason have we to use your so-called rationality as a standard for coercion when you yourself have admitted that it is against human nature? Understand that this response is not an argument against coercion but an argument against a particular justification. It may very well be that there is good reason to coerce people for their own good in some areas of life, but we should start with notions of “their own good” that actually makes sense for human beings.

And that is ultimately the problem, which the dog ownership example merely serves to bring to light. There is no realistic conception of a human good which includes only commensurable values. Better to shrink the calculation of utilitarianism into a subset of prudence than into an all encompassing reductionist philosophy of morality.