Abstract

Causal overdetermination, the existence of more than one sufficient cause for an effect, is standardly regarded as unacceptable among philosophers of mental causation. Philosophers of mind, both proponents of causal exclusion arguments and defenders of non-reductive physicalism, seem generally displeased with the idea of mental causes merely overdetermining their already physically determined effects. However, as I point out below, overdetermination is widespread in the broadly physical domain. Many of these cases are due to what I call the preservation of causal sufficiency. We need therefore to be precise about what unacceptable overdetermination amounts to in order to evaluate the prospects for a non-reductive account of mental causation. I argue that in order to have a good understanding of unacceptable overdetermination we should appeal to the notion of a minimal sufficient cause. In brief, a sufficient cause is minimal if it is sufficient to bring about the effect, but not more than sufficient. One way a cause could be more than sufficient for an effect is if its existence necessitates the existence of another (simultaneous) cause that is also sufficient for the same effect. In the second half of the paper I use this revised understanding of unacceptable causal overdetermination to show that the validity of the causal exclusion argument depends on strong readings of the principle of the causal self-sufficiency of physics. These strong readings can reasonably be questioned by a believer in non-reductive accounts of mental causation. This puts the burden of argument back on the causal exclusionist.