“But although realism does not add anything to the catalogue of entities or properties that a subjectivist believes to exist in the world, it does hold that certain truths that subjectivists think have to be grounded in something else do not have to be so grounded, but are just true in their own right. After all, whatever one's philosophical views, so long as there is such a thing as truth there must be some truths that don't have to be grounded in anything else. Disagreement over which truths these are defines some of the deepest fault lines of philosophy. To philosophers of an idealist persuasion it is self-evident that physical facts can't just be true in themselves, but must be explained in terms of actual or possible experience, just as it is self-evident to those of a materialist persuasion that mental facts can't just be true in themselves, but must be explained in terms of actual or possible behavior, functional organization, or physiology. The issue over moral realism is of the same kind.”