  Parfit makes a problematic move by deriving the normative claim that it is not rational to believe in non-cognitivism from a metanormative thesis about what it is to state such a claim. But it is easy enough to come up with other examples of epistemic self-defeat. Thus, consider an argument aimed at establishing global moral skepticism. Any such argument must invoke some epistemological principle via which the skeptical conclusion can be derived. So, if the argument applies just as well (mutatis mutandis) to epistemology and shows that we lack justified beliefs in that area as well, then it commits its advocates to thinking that one of its premises is not justified. This type of incoherence is presumably less worrying than the first one, as it neither rules out the validity of the argument nor the truth of its premises. But it is clearly sufficiently worrying to raise concerns about the target argument’s dialectical significance (see Sampson 2019 for discussion).