  Developing a plausible epistemology (intuitionist or otherwise) is also essential to meet some of the most pressing objections to non-naturalism. One such objection begins with the premise that non-natural properties do not figure in the best explanations of our experiences and observations. Gilbert Harman famously argues that prima facie there is a sharp contrast between moral beliefs and scientific beliefs on this score. The best explanation of scientific beliefs often seems to entail the truth of those beliefs—Harman gives the example of a scientist’s belief that a proton is in a cloud chamber which seems to be best explained, in part, by the actual presence of a proton in the chamber. By contrast, this does not seem to be true of our moral beliefs. Rather, people’s moral beliefs can be explained more elegantly and plausibly in terms of their upbringing and psychology without reference to any mysterious non-natural moral properties. This contrast, combined with the epistemological principle that we should believe in a property only if it figures in the best explanations of our experiences entails that non-naturalism should be rejected. Indeed, Harman’s argument would, if sound, also apply to anti-reductionist forms of naturalism. However, the anti-reductionist naturalist can try to avoid this line of argument by maintaining that the natural properties constituting moral properties do figure in the best explanations of our experiences. Nicholas Sturgeon, for example, argues that reference to the moral property of being oppressive figures in the best explanation of the growth of the anti-slavery movement in the United States between the Revolutionary War and the Civil War (see Sturgeon 1988: 245; see also Railton 1986), and this is but one of a range of examples discussed by Sturgeon (for a reply, see Blackburn 1990). However, this strategy is unavailable to the non-naturalist on many interpretations of what it is for a property to be a non-natural one. For example, if it is part of the definition of non-natural properties that they are not invoked in scientific explanations then this defense is unavailable. However, on some interpretations of non-naturalism this move is available. If, for example, non-natural properties are simply understood as properties that do not figure in similarity relations then the non-naturalist might argue that often the best explanation of our moral judgements actually does advert to moral properties. Intuitionism and its plausibility are likely to be relevant here. The non-naturalist might argue that people’s clear and distinct experiences of moral properties can be explained only as hallucinations of some kind in a naturalistic framework, and that this does not do justice to the clarity and ubiquity of such perceptions.