The issue here hinges on the acceptability of different kinds of systematic overdetermination (Bennett 2003). All can agree that it would be absurd if the physical effects of special causes always had two metaphysically independent causes. Plugging this into the causal closure argument for physicalism, we can conclude that there can be no metaphysically independent non-physical causes (such as Cartesian dualist mental causes) for effects that already have full physical causes. However, even if “strong overdetermination” by two ontologically independent causes is so ruled out, this does not necessarily preclude “weak overdetermination” by both a physical cause and a metaphysically supervenient special cause. Advocates of non-reductive physicalism argue that this kind of overdetermination is benign and consistent with the causal argument’s denial of strong overdetermination, since now the two causes are not metaphysically distinct—the special cause isn’t genuinely additional to the physical cause (nothing more is needed for your feelings than your brain states).