 These challenges may be ways of spelling out the force of G. E. Moore’s (1903) famous Open Question Argument: since it makes sense to grant that some X would be disapproved of by any impartial, informed, but otherwise normal observer, but nevertheless deny that X is morally wrong, there is reason to think that being disapproved of by an ideal observer is not the same thing as being morally wrong. To be sure, the Open Question Argument is contentious, and there are a number of standard responses: perhaps the identity of the properties is a posteriori, like that of water and H2O (Brink 1989), or perhaps it is an unobvious conceptual truth that we can read off the platitudes surrounding our concepts (Smith 1994). (See the entry on  moral naturalism.)