One of the rare points of agreement among moral and political philosophers is that, despite their innumerable physical and mental differences, all persons have equal moral standing (are moral equals, have the same natural rights, are owed equal concern and respect, etc.). There is a significant body of literature that asks which empirical feature of persons, if any, might ground this equality of standing, and a much larger one that asks which principles or policies might follow from it. However, strikingly, these discussions have for the most part proceeded on separate tracks. Here, by contrast, I want to bring them together. By getting clearer about what grounds the equal status of persons, we may hope to learn both why this status requires the equal distribution of any good among them and why that in turn requires the unequal distribution of wealth and other resources.

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If a given empirical property is the basis of a person's moral standing, and if all persons are moral equals, then it seems that all persons must possess that property to the same degree. This implication is problematic because people vary dramatically along every known empirical dimension. They differ not only in size, age, appearance, health, strength, intelligence, knowledge, and talent, but also in empathy, concern for others, and willingness to regulate their behavior in accordance with shared rules. They do, it is true, all belong equally to the species Homo sapiens. However, if this genetic commonality is to be significant, it must be because of the capacities it supports; and these, no less than other empirical properties, all come in degrees.