Against Structuralist Theories of Computational Implementation

Under what conditions does a physical system implement or realize a computation? Structuralism about computational implementation, espoused by Chalmers and others, holds that a physical system realizes a computation just in the case the system instantiates a pattern of causal organization isomorphic to the computation‟s formal structure. I argue against structuralism through counter-examples drawn from computer science. On my opposing view, computational implementation sometimes requires instantiating semantic properties that outstrip any relevant pattern of causal organization. In developing my argument, I defend antiindividualism about computational implementation: relations to the social environment sometimes help determine whether a physical system realizes a computation. 1 The physical realization relation 2 Semantics and computational implementation 3 Conforming to instructions 4 Implementing a computer program 4.1 The denotational semantics of Scheme 4.2 Worries about intentionality 4.3 Worries about the natural numbers 5 Implementing a machine model 6 Bounded structuralism