  Sometimes the intuitionist’s perceptual characterization of moral knowledge is metaphorical. The idea is that moral knowledge is not literally perceptual in the first instance but is somehow very much like perceptual knowledge. This approach has its advantages. In trying to make sense of the idea of moral perception of non-natural properties, some intuitionists have maintained that our ability to have veridical experiences of the moral properties is in virtue of our having a special faculty of mind whose function is to detect such properties. This raises a number of questions about the origin and functioning of such a faculty. An account that claims only that moral knowledge is somehow like perceptual knowledge need not face these difficulties. Of course, such accounts run the risk of being too vague to be helpful unless some less metaphorical account of moral knowledge is forthcoming. Even those who take the idea or perceptual moral knowledge literally are not thereby committed to belief in such special faculties. Perhaps moral perception is continuous with other ordinary forms of perception even if it is literally the perception of a non-natural property. If non-natural properties are by definition causally inert then this position seems problematic. On other ways of understanding non-natural properties, though, whether there is a problem will depend on further controversial philosophical questions. For example, if non-natural properties are understood as properties that would not figure in the best scientific account of reality then the issue obviously concerns the authority of science to determine the answers to all ontological questions. Non-naturalists sometimes accuse their opponents of crude scientism for assuming that science has such authority and this brings out some deeper methodological differences between naturalists and non-naturalists (see below, “Methodology”).