I have yet another criticism of contemporary ethics.
Hume pointed out that prescriptions do not follow logically from descriptions.
Most contemporary ethicists assume that they do.
Most contemporary ethicists derive prescriptions from descriptions by means of the hypothesis that moral properties are supervenient properties.
This moral property supervenes on these natural properties. These natural properties obtain. Therefore, this moral property obtains.
The first premise is a description, not a prescription. It is not the kind of moral principle that shows up in elementary textbooks to illustrate Hume’s observation.
Worse, there is no evidence of any sort that any claim of the type is true. There is no empirical evidence, no logical proof, and no conceptual analysis that shows that it is true.
I am aware that if two actions are otherwise identical, then it is impossible for one to be right and the other wrong, say.
But it does not follow that moral properties are supervenient properties.
Instead, it could be the case that it is impossible for one action to be right and the other wrong because it is impossible for both to be compatible with a moral principle. (More precisely perhaps, it is impossible for their true descriptions both to be compatible.) A legal analogy helps here. If a new statute is enacted, actions are either compatible with it or not. But we never say that the lawfulness (or unlawfulness) of the actions supervenes on their non-legal properties. If supervenience talk is superfluous in the legal case (and it is), it could be superfluous in the moral case as well. Furthermore, if “supervenience” is defined so broadly (and its meaning is stipulated by philosophers) that it includes the consistency case, then it is defined so broadly that it mystifies rather than clarifies.
Mystification enables the implausible to abstract credibility from the plausible. It is no virtue.