 What is Mackie’s argument for his ontological claim? This is set out in his ‘argument from queerness’ (Mackie has another argument, the ‘argument from relativity’ (or ‘argument from disagreement’) (1977: 36–38), but this argument cannot be discussed here for reasons of space. For a useful discussion, see Brink (1984)).The argument from queerness has both metaphysical and epistemological components. The metaphysical problem with objective values concerns ‘the metaphysical peculiarity of the supposed objective values, in that they would have to be intrinsically action-guiding and motivating’ (49). The epistemological problem concerns ‘the difficulty of accounting for our knowledge of value entities or features and of their links with the features on which they would be consequential’ (49). Let’s look at each type of worry more closely in turn.