Many philosophical discussions embody a structuralist conception of computation: a computational model describes an abstract causal structure, without taking into account particular physical states that instantiate the structure. This conception traces back at least to Putnam’s original treatment (1967). Chalmers (1995, 1996a, 2011, 2012) develops it in detail. He introduces the combinatorial-state automaton (CSA) formalism, which subsumes most familiar models of computation (including Turing machines and neural networks). A CSA provides an abstract description of a physical system’s causal topology: the pattern of causal interaction among the system’s parts, independent of the nature of those parts or the causal mechanisms through which they interact.  Computational description specifies a causal topology.