A rather different argument appeals not so much to a metaphysical need for principles as to an epistemological need. If there is a distinction between right and wrong actions, how are we to detect it? There must be a detectable difference between the properties of the right ones and the properties of the wrong ones. Now if an action is wrong, it is wrong because of certain other features it has—the non-moral features that make it wrong. Those non-moral features will be detectable in the ordinary