Over at the Online Consciousness Conference, which is now in it’s second week, David Chalmers has advanced an argument that Russellian Monism is not a form of epiphenomenalism, On RM there are phenomenal, or protphenomenal, properties that serve as the categorical bases for the dispositional properties that physics talks about. So on this view mass, charge, spin, etc are the visible face, so to speak, of these fundamental phenomenal, or protophenomenal, properties. The zombie world, then, is one that has the same dispostitions –mass, charge, spin, etc– but lacks the protophenomenal/phenomenal properties that serve as the categorical bases. This can happen in one of two ways. The first is by having a different set of categorical bases that were not related to consciousness, the second by having just the structural properties with no categorical bases. In the first instance the new fundamental properties would take over the causal work that the propphenomenal properties had done before. But just because they are now causing behavior doesn’t show that the protophenomenal properties that are postulated by RM can’t have causal powers. The second possibility seems a bit weird. How can we have disposition properties like mass and charge without any kind of categorical base? But assuming that we can make sense of this idea Dave suggested that we should not hold it against the idea that the categorical bases that these dispositions actually have are causally efficacious. I think I am less sympathetic to this suggestion and would wonder why we should accept it, but someone who like RM could simply reject that such a world is conceivable. RM is a strange view but it is a bit better than epiphenomenalism.
Also in the discussion Dave says that he takes the best argument against epiphenomenalism to be the argument from coincidence. Epiphenomenalism makes it a lucky accident that behavior always lines up with qualia. He acknowledges that this is not fatal, as it may be shown that we should accept these laws anyways, but it is a prima facie point against the epiphenomenalist that RM doesn’t share.