Causal Exclusion and Physical Causal Completeness

Nonreductive physicalists endorse the principle of mental causation, according to which some events have mental causes: Sid climbs the hill because he wants to. Nonreductive physicalists also endorse the principle of physical causal completeness, according to which physical events have sufficient physical causes: Sid climbs the hill because a complex neural process in his brain triggered his climbing. Critics typically level the causal exclusion problem against this nonreductive physicalist model, according to which the physical cause is a sufficient cause of the behavioural effect, so the mental cause is excluded from causally influencing Sid’s behaviour. In this paper I demonstrate how numerous nonreductive physicalists have responded to the causal exclusion problem by weakening the principle of physical causal completeness in numerous ways. The result: either numerous nonreductive physicalist solutions fail on account of the fact that they do not satisfy a robustly defined principle of physical causal completeness, or there is an accelerating trend of solving the causal exclusion problem by suitably weakening the principle of physical causal completeness.