  This defence of Moore's argument does not address a different concern, namely that the argument applies only to versions of ethical naturalism which involve a definition of ethical value, and thus that naturalist positions which maintain that ethical value is an irreducible natural property are not touched by the argument. Moore's argument against positions of this kind rests on the claim that the ethical value of a situation is not a feature of it which is independent of its other properties; on the contrary it depends on its other properties. As he puts it in the preface he composed for the second edition of Principia Ethica, but never actually published, a thing's ‘intrinsic value’ depends on its ‘intrinsic nature’, and he glosses this dependence in terms of the relationship which we now call ‘supervenience’ (though Moore does not use the term): things with the same intrinsic nature, or natural properties, must have the same intrinsic value (see ‘The Conception of Intrinsic Value’ 286). Moore took it that supervenience was not an inherently reductive relationship, and thus that it was consistent for him to hold that goodness is not a natural property even though it supervenes upon natural properties; but, he assumed, if one takes the view that goodness is itself a natural property, the fact that it supervenes upon other natural properties makes it impossible to avoid a reductive thesis. So the supervenience of intrinsic value removes the option of a non-reductive naturalism without contradicting his version of ethical non-naturalism.