You’re most welcome, & many thanks for your question.
I just replied to a similar question on another platform, so will paste that here directly below, between rows of asterisks —
***
Ethical or moral naturalism is a wily beast, & (to switch metaphors) a bump in the carpet, which, when flattened, always pops up again somewhere else.
Hume’s point is just the conceptual one that if someone lists a number of facts about the way things actually are (the “is”), & then concludes that things morally should be that way (the “ought”) then that’s a logically invalid argument & a fallacy.
Moore’s point is (intended to be) deeper, namely that any attempt to explain the highest moral value (the highest good, The Good, the Categorical Imperative, etc.), in terms of a set of purely natural (= factual, empirical, sensory-psychological, material or physical) properties, will always fail & is a fallacy.
One problem here is that there are many different varieties of ethical or moral naturalism, including psychological ones like hedonism, egoism, & Utilitarianism, & biological ones like Darwinian or evolutionary ethics, plus various forms of moral relativism, so naturalists will typically claim that their favored variety avoids the problems of other varieties.
But a deeper problem is that Moore failed to distinguish between
different ways that one might try to explain X in terms of Y: (i) identification of definitions (“X” means the same as “Y”), (ii) identification of properties (the property of being X = the property of being Y, even when their definitions are different), (iii) logical supervenience of X-properties on Y-properties (such that Y-properties logically necessitate X-properties & logically necessarily there cannot be a change in anything’s X-properties without there also being a corresponding change in its Y-properties, & (iv) natural or physical supervenience of X-properties on Y-properties (such that Y-properties naturally or physically necessitate X-properties, & naturally or physically necessarily there cannot be a change in anything’s X-properties without there also being a corresponding change in its Y-properties).
This may all seem esoteric, over-subtle, & mind-fogging — & it is — but the bottom line is that arguments against one kind of naturalism don’t necessarily hold against other kinds, & most naturalists nowadays defend either a (iii)-type naturalism or a (iv)-type naturalism, the latter of which is particularly difficult to argue against, since it’s actually consistent with Hume’s conceptual point, i.e., it’s what called a “non-reductive naturalism,” & it also relies on mechanistic empirical natural science, which to most people seems irrefutable.
So, my view is that Kantian approaches are anti-naturalistic; but refuting (iv)-type naturalism is philosophically strenuous, since it requires rejecting the mechanistic conception of human behavior & replacing it with an anti-mechanistic, biologically real, scientifically well-supported conception of (metaphysical, not political) libertarian rational human free will AND providing compelling imaginary modal-metaphysical counterexamples to all the leading naturalistic theories, both of which I’ve tried to do in that piece I posted yesterday.
— Of course, since either (iii)-type naturalism or (iv)-type naturalism is the default position of most professional academic philosophers, & also (at least implicitly) of most people who believe in science, then the easiest way to “refute” the sophisticated anti-naturalistic position I’ve just sketched, is for them simply to ignore it, which is what they generally do, alas….
***
