  Nonetheless, simply characterizing non-naturalism in terms of Moore’s view is not very helpful for at least three reasons. First, we still need some way of determining which dimensions of similarity to Moore’s views are the relevant ones. This is a standard problem with trying to understand a genus in terms of a particularly salient species thereof. Second, Moore defended a variety of theses about goodness in Principia which have been referred to as forms of non-naturalism, so we are then left with the question what these views have in common in virtue of which they are all forms of non-naturalism. Third, Moore’s non-naturalist account of goodness in Principia is itself unclear in certain crucial respects. Indeed, his later “Reply to My Critics,” Moore himself admitted that his attempts in Principia to explain in what sense goodness was a non-natural property were untenable (Moore 1942: 582). Nonetheless, Moore’s account in Principia is important to bear in mind when trying to characterize non-naturalism in meta-ethics. For a plausible constraint on any such characterization is that it not imply that Moore clearly did not put forward a form of non-naturalism in Principia. With this constraint in hand, we are in a position to develop a more general characterization of non-naturalism.