Stephen Clark puts it this way: Any merely materialistic or naturalistic metaphysician must have considerable difficulty in accommodating any rules of evidence. If what I think is the echo or epiphenomenon merely of material processes, so that my thought is what it is because my neural chemistry is what it is, it seems very difficult to see how that thought can be one that I ought to have or ought not to have. It might of course be better (because more accurate?) if I did, or if I did not, but I