This paper is a survey of the supervenience challenge to non-naturalist moral realism. I formulate a version of the challenge, consider the most promising non-naturalist replies to it, and suggest that no fully effective reply has yet been given.

It is widely held, even among nonnaturalists, that the moral supervenes on the natural. This is to say that for any two metaphysically possible worlds w and w′, and for any entities x in w and y in w′, any isomorphism between x and y that preserves the natural properties preserves the moral properties. In this paper, I put forward a conceivability argument against moral supervenience, assuming non-naturalism. First, I argue that though utilitarianism may be true, and the trolley driver (...) is permitted to kill the one to save the five, there is a conceivable scenario that is just like our world in all natural respects, yet at which deontology is true, and the trolly driver is not permitted to kill the one to save the five. I then argue that in the special case of morality, it is possible to infer from the conceivability of such a scenario to its possibility. It follows that supervenience is false. (shrink)

_ Source: _Page Count 22 In _Unbelievable Errors_, Bart Streumer offers resourceful arguments against each of non-reductive realism, reductive realism, and non-cognitivism, in order to motivate his version of the normative error theory, according to which normative predicates ascribe properties that do not exist. In this contribution, I argue that none of the steps of this master argument succeed, and that Streumer’s arguments leave puzzles about what it means to ascribe a property at all.