  There are two main responses to such skeptical hypothesis arguments (cf. May 2013).  First, some anti-skeptics deny (1) and claim that skeptical hypotheses can be ruled out somehow. They might argue that moral nihilism is internally inconsistent or meaningless. If so, it can be ruled out by logic and semantics alone. However, moral nihilism does seem consistent and meaningful, according to all plausible theories of moral language, including expressivism, realism, and constructivism (Sinnott-Armstrong 2006, chap. 3). Moral nihilism is also not subject to the kind of argument that Putnam (1981) deploys against more general skeptical scenarios. Anti-skeptics still might argue that moral nihilism is incompatible with some non-moral facts or observations or their best explanations. If so, it can be ruled out by arguments with only non-moral premises. However, all such attempts to cross the dreaded is-ought gap are questionable (Sinnott-Armstrong 2006, chaps. 7–8). A third way to rule out moral nihilism would be based on common moral beliefs that are incompatible with moral nihilism. However, just as it would beg the question to use common beliefs about the external world to rule out a deceiving demon hypothesis, so it would also beg the question to argue against moral nihilism on the basis of common moral beliefs — no matter how obvious those beliefs might seem to us, and no matter how well these common beliefs cohere together (Sinnott-Armstrong 2006, chaps. 9–10). Moral skeptics conclude that there is no way to rule out moral nihilism, just as premise (1) claims.