Critics of utilitarianism usually rule out interpersonal aggregation. Many of them (e.g. Rawls, Nozick, and Nagel) appeal to the notion of the separateness of persons. According to them, we should rule out aggregation because aggregative principles do not take the separateness of persons seriously. This is a very familiar claim in moral and political philosophy. But I did not understand this claim. I now know why I did not understand it: Either (a) this claim is a truism or (b) it does not make sense.