Moral properties would supervene upon non-moral properties and be conceptually autonomous. That, according to Simon Blackburn, would make them if not impossible at least mysterious, and evidence for them best explained by theorists who say they are not real. In fact moral properties would not challenge in ways Blackburn has contended. There is, however, something new that can be gathered from his arguments. What would the supervenience of moral properties and their conceptual autonomy from at least total non-moral properties entail (...) not only for Intuitionists, who ‘knew this all along,’ but for all moral realists, that there are synthetic necessary moral principles? There is for all moral realists the problem of explaining ‘what in the world’ makes possible these necessities. (shrink)