Jaegwon Kim argues that unreduced mental causes are excluded from efficacy because physical causes are sufficient in themselves. One response to this causal exclusion argument is to embrace some form of overdetermination. In this paper I consider two forms of overdetermination. Independent overdetermination suggests that two individually sufficient causes bring about one effect. This model fails because the sufficiency of one cause renders the other cause unnecessary. Dependent overdetermination suggests that a physical cause is necessary and sufficient for a given (...) effect, but it necessitates a mental cause of the effect as well. This model fails because the necessity of the mental cause renders the physical cause individually insufficient. (shrink)