 It would be difficult to find a better anticipation of the mind-body problem as we know it today. The problem of mental causation may not be exactly the same as Descartes’ problem, but it is nonetheless inherited by anyone who insists that mental properties must, on the one hand, make a causal difference and by those who, on the other, think that physics is a closed causal system. Just as mind-body interaction was a problem for substance dualism, so is mental causation still the problem facing the many varieties of (both reductive and non-reductive) physicalism (Kim, 29-30).