What should children be served with, mayonnaise or mustard? No, I don’t think you read that wrong. If children—let me be clear about this: I mean dead, slaughtered, and fried human children—are served for dinner, should they be served with mayonnaise or mustard?

Yes, the question is bizarre. But, consider this: Utilitarians can answer it.

To them, the question’s not even that hard. One option is better in terms of how much happiness it produces, and therefore there’s a better and a worse choice. A diner at the bizarre feast, the utilitarian would argue, could make the morally wrong choice between mayonnaise and mustard.

Now, consider the following, which utilitarians can’t answer.

In one distribution of goods, Anna has 1 welfare unit and Beth has 9. In a second distribution, each have 5 welfare units. In both distributions, the total amount of welfare units is 10. Which distribution of goods is better?

Utilitarianism is only concerned with the total amount of happiness. It does not care about how that total amount is distributed. Utilitarianism is insensitive to the very reasonable intuition that an equal distribution of goods is better. Ceteris paribus, Anna and Beth should have 5 welfare units each.

Thus, utilitarianism provides guidance in the first case, which we don’t care about, but not in the second case, which we really do care about.

In some sense, utilitarianism has a reality problem. It fails us when we need it but is there for us when we don’t. Other normative theories also have that problem. Consider, for instance, rights based libertarianism.

Suppose an extremely patriarchal but libertarian society. Everyone’s rights are fully respected, but cultural norms tie women to certain low-paid occupations, strict dress codes, a subjective behavior toward men, and so on. Per libertarian standards, everything is just fine: No rights are violated.

Now, suppose that in that society, a law is passed prohibiting people from staring directly into the sun for more than five minutes per day. Although no-one ever does that, per libertarian standards, everyone has the right to do so if they wish. Therefore, libertarians would oppose the law. Don’t tread on me!

Thus, like utilitarianism, rights based libertarianism has a reality problem.

I think that the reality problem, or rather the reality test, is a quality mark of normative theorizing. While being normatively over-determinative in some respects, theories that suffer from the reality problem are under-determinative in others. They are not aligned with how people actually lead their lives, and thus fail to be relevant to anyone who is interested in leading a moral life.

But, that’s from the perspective of an applied ethicist. I’m interested in how normative theories are applied, rather than in which normative theory or theories that are true (if, at all, we can speak of them as ”true” and ”false”). To me, the reality problem is significant. To other philosophers, it might not even be an issue. What’s true is true; what people do with truths is something else.