 First, moral anti-realism is not a form of moral skepticism. If we take moral skepticism to be the claim that there is no such thing as moral knowledge, and we take knowledge to be justified true belief, then there are three ways of being a moral skeptic: one can deny that moral judgments are beliefs, one can deny that moral judgments are ever true, or one can deny that moral judgments are ever justified. The noncognitivist makes the first of these denials, and the error theorist makes the second, thus noncognitivists and error theorists count as both moral anti-realists and moral skeptics. However, since the non-objectivity of some fact does not pose a particular problem regarding the possibility of one’s knowing it (I might know that a certain diamond is worth $1000, for example), then there is nothing to stop the moral non-objectivist from accepting the existence of moral knowledge. So moral non-objectivism is a form of moral anti-realism that need not be a form of moral skepticism. Conversely, one might maintain that moral judgments are sometimes objectively true—thus being a moral realist—while also maintaining that moral judgments always lack justification—thus being a moral skeptic. (See entry for  moral skepticism.)