The Supervenience Challenge to Non-Naturalism

It is impossible that one action is morally impermissible and another permissible unless they dier also in some other respect; perhaps one involves stealing but the other doesn’t. One person cannot be morally better or more virtuous than another without there being some other dierence between them, such as that one is more reliably disposed to help others or to keep her promises. It cannot be that you have a reason to run for the bus on one occasion but no reason to do so on another if the situations dier in no other qualitative respect, such as how ecient each action will be for achieving your aims or for doing something good. If two persons are qualitatively exactly alike (or “indiscernible”) in all other ways, they cannot but be morally alike as well.