Supervenience and Implementation: Virtual and Physical Machines

How can a virtual machine X be implemented in a physical machine Y? We know the answer as far as compilers , editors, theorem-provers, operating systems are concerned , at least insofar as we know how to produce these implemented virtual machines, and no mysteries are involved. This paper is about extrapolating from that knowledge to the implementation of minds in brains. By linking the philoso-pher's concept of supervenience to the engineer's concept of implementation, we can illuminate both. In particular, by showing how virtual machines can be implemented in causally complete physical machines, and still have causal powers, we remove some philosophical problems about how mental processes can be real and can have real eeects in the world even if the underlying physical implementation has no causal gaps. This requires a theory of ontological levels.