Hume on ‘is’ and ‘ought’

Sometimes in the history of philosophy the defence of a particular philosophical position and the interpretation of a particular philosopher become closely identified. This has notoriously happened more than once in the case of Plato, and lately in moral philosophy it seems to me to have happened in the case of Hume. At the centre of recent ethical discussion the question of the relationship between factual assertions and moral judgements has continually recurred, and the nature of that relationship has usually been discussed in terms of an unequivocally sharp distinction between them. In the course of the posing of this question the last paragraph of book III, part i, section i, of Hume’s Treatise has been cited over and over again. This passage is either quoted in full or at least referred to — and with approval — by R. M. Hare,1 Professor A. N. Prior,2 Professor P. H. Nowell-Smith,3 and a number of other writers. Not all contemporary writers, of course, treat Hume in the same way; a footnote to Stuart Hampshire’s paper, ‘Some Fallacies in Moral Philosophy’,4 provides an important exception to the general rule. But very often indeed Hume’s contribution to ethics is treated as if it depended largely on this one passage, and this passage is accorded an interpretation which has acquired almost the status of an orthodoxy. Hare has even spoken of ‘Hume’s Law’.5