  Alternatively, the non-naturalist might maintain that the practicality requirement on motivation is a trifling semantic truth. The idea would be that to be fully rational in part just means doing what one believes to be right. However, this move differs from the second reply considered above in that it is a clear attempt to define a normative notion (rationality) in purely naturalistic terms. This last claim assumes we can give a naturalistic account of rationality, which is not obviously correct given non-naturalism about rightness, but neither is it obviously incorrect. In any event, such an analysis of rationality sits poorly with the non-naturalist’s standard appeal to the Open Question Argument. For if the Open Question Argument is sound for moral predicates like ‘morally required’ then one might have thought that analogous arguments would go through for ‘rational’ and ‘irrational’. After all, rationality is plausibly a normative notion and on some accounts (see above) it is the idea of normativity that gives the Open Question Argument its force. This is one reason the practicality requirement on moral judgement is especially a problem for non-naturalists, since naturalists are not committed to accepting the soundness of the Open Question Argument in the moral case.