  The open question argument has not been persuasive for several reasons. Two are especially notable. Moore’s target was the moral naturalist who thought that the identities in question might be established on the basis of conceptual analysis. It has been pointed out, however, that the question might still be open for someone provided that this person is not aware of the identity, not having carried out the analysis (Brandt 1959). Current versions of moral naturalism, moreover, do not propose that the identity would be known by a priori reasoning. The identity is conceived instead to be analogous to those identities discovered in the sciences, such as the identity claimed to exist between genes and strings of DNA or the well-accepted identity between water and H2O. Obviously, whether genes are DNA or whether water is H2O have been open questions at one time. In the case of DNA the question is still open for some. The reason is that these identities are established a posteriori. Perhaps Moore is right to deny the putative identity, but his open question argument fails to establish that he is.