According to Parfit's Triviality Objection, metaethical naturalism can't adequately capture our ability to make substantive positive normative claims. For example, suppose a subjectivist naturalist wants to hold both:
Normative Subjectivism: You have reasons for action just when that act would fulfill one of your desires; and
Reductive Thesis: What it is to have a reason for action just is for that action to be such as to fulfill one of your desires.
Parfit responds that, if the Reductive Thesis were true, Normative Subjectivism could no longer state a positive substantive normative fact, since it would not be attributing any further normative property to acts that fulfill one of your desires. It would just be to re-attribute that same property under another guise, and so the only real normative fact in the vicinity would be the negative one that there is no further normative property of being a reason that acts may have when they have the property of being such as to fulfill your desires (or whatever).
Schroeder responds, in 'What Matters about Metaethics' (forthcoming, pp.7-8), that on his view positive normative claims are still possible because the attribution of reasons pragmatically implicates that the reasons in question are relatively weighty ones. And the property of being a weighty reason is a further normative property, just as Parfit asked for.
I have a couple of worries about this response. Firstly, Schroeder is relying on pragmatic implicatures from normative claims in order to explain their status as positive substantive normative claims, but implicature is cancellable. So consider the following putatively positive substantive normative claim:
Normative Subjectivism with Cancelled Implicature (NSwCI): You have reasons for action just when that act would fulfill one of your desires -- but these reasons need not be very weighty at all.
How can Schroeder explain NSwCI's status as a positive normative claim? What further normative property does it attribute to acts that are such as to fulfill one of your desires? It certainly doesn't attribute the normative property of being supported by weighty reasons -- it explicitly pre-empts any such attribution of normative weight. But it is surely still a positive substantive normative claim if anything is. So, I conclude, Schroeder has failed to adequately address the Triviality Objection.
Secondly (and really just an afterthought), presumably Normative Subjectivism was intended to be understood along the lines of NSwCI all along -- Schroeder explicitly denies that all reasons are weighty reasons, after all, so when stating the general conditions for something being a reason (namely, that it explains how so acting would contribute to the fulfillment of your desires, or something like that), he can't also be intending to pragmatically implicate that all these reasons are weighty reasons. Which makes his "implicature" response to Parfit all the more puzzling.
Am I missing something?
[Update: Mark Schroeder tells me that the dialectic I'm picking up on here is not intended to be central to his response to Parfit.]