  The situation is more complex, however, for the other form of moral naturalism. It maintains that moral facts are natural facts but denies that they are specifiable using the language of the natural and social sciences (Kim 1978, Sturgeon 1985, Brink 1989). Moral facts are said to be natural facts in that they are discoverable empirically and provide causal explanations of events in the natural world. At the same time, they are a unique category that defies identification in non-moral terms. As such, they raise again the issue of redundancy. Do we really need this special category of natural facts in order to understand the natural world? In this view some natural facts are supposed to supervene on others. That is to say, moral facts are dependent on distinct natural facts specifiable in non-moral terms in the following way: if the moral facts were otherwise, necessarily the distinct non-moral facts on which they depend would have to be different. Take a deliberate act of cruelty done just for fun. This act is wrong in virtue of being a deliberate act of cruelty done just for fun. The fact that it is a wrong act and the fact that it is deliberately cruel done for fun are distinct facts, but the first depends on the second. Necessarily, if what was done had not been wrong, it would not have been a deliberate act of cruelty done for fun. Once this relation of supervenience is recognized, it is possible to defend the non-redundancy of moral facts by pointing out parallel relations of supervenience in the non-moral natural world and arguing that the redundancy objection proves too much, asking us to reject other non-moral categories that appear ontologically sound. For example, genetic facts obtaining at the cellular level are said to supervene on genetic facts at the molecular level without one being simply identical with the other (Kitcher 1984), yet it would be absurd from a scientific perspective to deny the existence of facts at the cellular level. Whether this defense is ultimately successful remains to be seen, but at the present time it is far from clear that either form of naturalism can be rejected on grounds of redundancy (Sayre-McCord 1988).