The G. E. Moore of later ethical writings did not invoke this set of criteria to draw the natural/non-natural distinction. Beliefs in mathematical orlogical necessary truths best exemplify this type of epistemic justification. For Moore, moral knowledge is simply another kind of a prioriknowledge of necessary truths. Moore made no appeal to a quasi-perceptual faculty of moralintuition. Moore gave abundant evidence of a similar view not only in Principia but also in The Elements of Ethics. In Principia Ethica, Moore regarded qualifying rules of commonmorality as prescribing acts and omissions that are good as means andillustrated this claim with an analysis of the instrumental value of the effectof acting according to the negative command ‘Do not murder’. Evolutionary theorists in ethics seem now in a position to claim that their challenge rests neither on a reductive naturalistic definition of a key ethical concept, nor on an inference about what people ought to do from a premise entirely about the course of evolution.