Sinnott-Armstrong's paper principally defends our inability to justify, philosophically, normal moral claims. In particular, we cannot justify them against other claims, especially the claim of moral nihilism. Moral nihilism is the doctrine that there are no moral obligations (for anybody to do anything). This thesis ‘does not lie in meta-ethics. It is a universally quantified substantive moral claim’ (p. 219). Sinnott-Annstrong makes it clear that he does not actually believe this doctrine (p. 217), but he believes that it is coherent, and that a variety of strategies philosophers might attempt all fail to disprove it. And because of this, ordinary claims to obligation are philosophically unjustified.