How To Be a Moral Platonist

Contrary to popular opinion, non-natural realism can explain both why normative properties supervene on descriptive properties, and why this pattern is analytic. The explanation proceeds by positing a subtle polysemy in normative predicates like “good”. Such predicates express slightly different senses when they are applied to particulars (like Florence Nightingale) and to kinds (like altruism). The former sense, “goodPAR”, can be defined in terms of the latter, “goodKIN”, as follows: x is goodPAR iff there is a kind K such that x is a token of K, and K is goodKIN. Now if x and y are descriptively exactly similar, then they are tokens of exactly the same kinds, so x is a token of a goodKIN kind if and only if y is. Therefore, by the definition, x is goodPAR if and only if y is. Supervenience just falls out of the definition of “goodPAR