 Making sense of the action-guiding character of moral language is not, of course, the only motivation for expressivism. Another important part of the case for it is the Argument from Moral Supervenience, originally made by Blackburn (1971; 1985), which claims, roughly, that expressivists can best explain why it is a conceptual truth that descriptively identical worlds must be morally identical. For more, see the entry on  Supervenience in Ethics.