  If the reality of property dualism is not to be denied, but the problem of how the immaterial is to affect the material is to be avoided, then epiphenomenalism may seem to be the answer. According to this theory, mental events are caused by physical events, but have no causal influence on the physical. I have introduced this theory as if its point were to avoid the problem of how two different categories of thing might interact. In fact, it is, at best, an incomplete solution to this problem. If it is mysterious how the non-physical can have it in its nature to influence the physical, it ought to be equally mysterious how the physical can have it in its nature to produce something non-physical. But that this latter is what occurs is an essential claim of epiphenomenalism. (For development of this point, see Green (2003), 149–51). In fact, epiphenomenalism is more effective as a way of saving the autonomy of the physical (the world as ‘closed under physics’) than as a contribution to avoiding the need for the physical and non-physical to have causal commerce.