  Now of course moral realists can consistently acknowledge this and then argue against naturalism—perhaps, at least in part, on the grounds that naturalism is incompatible with acknowledging moral facts. This was, in fact, Moore’s position. Yet one then has the burden of explaining how moral facts are related to natural facts and the burden of explaining how we might manage to learn of these non-natural facts. A good deal of the work that has been done defending moral realism is devoted either to meeting these burdens or to showing that they do not pose a special problem just for morality. Moral realists of this sort allow that moral facts are not natural facts, and moral knowledge is not simply of a piece with scientific knowledge, even as they defend the idea that there are moral facts and (at least in principle) moral knowledge. They thus reject the idea that science is the measure and test of all things (Shafer-Landau 2003, Parfit 2011, Scanlon 2014).