  It is also sometimes suggested that non-naturalism is the thesis that moral properties are sui generis and irreducible (see, e.g. Pigden 1993: 421–422), and indeed this is one of the most distinctive aspects of Moore’s account of goodness. However, this is not the best way to understand non-naturalism. For intuitively whether a property is natural is orthogonal to whether it is sui generis. We should preserve conceptual space for properties that are natural and irreducible (fundamental properties of physics are perhaps the least controversial examples, but many would argue that the fundamental properties of psychology and sociology are also irreducible but natural) as well as properties that are non-natural but reducible to other non-natural properties (perhaps rightness is reducible to goodness or vice versa even if both are non-natural). Indeed, Moore himself was at one stage a non-naturalist about rightness but nonetheless thought that rightness was reducible to the property of being the action with the best outcome, though he later abandoned this view. Furthermore, a number of self-styled contemporary naturalists hold that moral properties are both natural and irreducible (Richard Miller and Nicholas Sturgeon, for example) and we should try to accommodate this characterization of their view. In Principia Moore often (though not always – he considers the example of yellowness) seems to ignore the fact that a property might be both natural and irreducible.  Undoubtedly this has led to some confusion in later discussions of naturalism and non-naturalism (for useful discussion of Moore on this point, see Baldwin 1990: 83–84).