  The open question argument can be seen as providing independent support for what is sometimes called Hume’s Law – the claim that one can never validly deduce an ‘ought’ from an ‘is’ (Hume 1888, 469). According to Hume’s Law, no set of premises consisting entirely of non-moral descriptive statements is sufficient to entail a moral or normative conclusion. The non-cognitivist is in a position to explain this, insofar as her positive proposal for the functioning of moral terms will suggest they do more than merely describe the world. She will say that moral terms essentially express a positive attitude, or function to commend. Purely descriptive terms do not. Nothing can be the conclusion of a valid argument which is not already implicit in the premises. Thus descriptive claims cannot entail the extra expressive or imperatival component that according to the non-cognitivist is part of the meaning of moral terms (Hare 1952, 32–49).