The irreducibility of normativity is a mixed bag nowadays. There are intuitionists like Michael Huemer or Robert Audi(?) who I think advance the thesis tout court, but otherwise it still does show up in veiled forms. For example, start out from part of the SEP gloss of metaepistemology:
Terence Cuneo’s (2007) defense of metaepistemological realism also comes in the service of a further objective, in Cuneo’s case, a defense of metaethical realism. Cuneo’s master argument is as follows:
- If moral facts do not exist, then epistemic facts do not exist.
- Epistemic facts exist.
- So, moral facts exist.
- If moral facts exist, then moral realism is true.
- So, moral realism is true (Cuneo 2007: 6)
Now piece this together with a claim that the concept of knowledge is itself irreducible, and you have a recipe for a Moore-Ross deontic irreducibility claim, too.
Still, for all that, the stronger your irreduction, the more absurd-seeming your gloss of deontic concepts. Rawls puts it like so (A Theory of Justice, 1999 ed., pg. 418):
Ross holds that the sense of right is a desire for a distinct (and unanalyzable) object, since a specific (and unanalyzable) property characterizes actions that are our duty. ... But on this interpretation the sense of right ... resembles a preference for tea rather than coffee... to make it regulative of the basic structure of society is utterly capricious...
So note that there is still room for discursive reflection on even irreducible deontic concepts: Prichard found space to argue over what the irreducible property of rightness attaches to, saying that it was not possible actions directly, but the agents who are under obligation, to which the predicate of obligation intrinsically applies.