In metaethics, moral irrealists argue that moral facts are neither ontologically real nor mind-independent. In moral semantics, irrealists who are descriptivist error theorists argue that typical moral claims attempt to report descriptive moral facts but that such facts do not exist, so typical moral claims are descriptively false or erroneous. Moral irrealists who are non-descriptivists, such as Mark Timmons, argue for a different function of moral claims. Timmons argues that moral claims attempt to guide action. He further maintains that moral claims can be true or false, but not according to a descriptivist function (he affirms cognitivism but denies descriptivism). I lay out Timmons‘ semantics and grapple with a number of objections to his view. I conclude that Timmons ought to discard his contextual truth-apt semantics and his non-descriptivism; instead he should defend the prescriptive, or evaluative, function of moral claims within an overarching descriptivist error theory. / Graduate / 0422