In this century the major insight in the field of moral philosophy has been that moral arguments need not proceed by way of the deduction of moral conclusions from non-moral premises. This realisation sprang from a recognition that the purpose of moral argument was not just to get one party to a moral disagreement to assent to a proposition that at the outset of the discussion he denied. If a moral argument was to be able to be considered successful it was insufficient for someone to recognise that an action he had previously considered right was wrong; it was essential that this recognition have an influence on his subsequent conduct. The change in belief was important only in so far as it led to a change in action. And although this insight led people to over diminish the importance of belief and propose various types of non-cognitive theories of ethics, it is none the less true that the acceptance of a proposition of the form ‘action X is wrong’ must have an impact of some kind on the behaviour of those who accept it.