Most of the philosophers who discuss computation are interested in computation because they are interested in the computational theory of cognition. Cognitive systems are typically assumed to represent things, and computation is supposed to help explain how they represent. So many philosophers conclude that computation is the manipulation of representations. Or perhaps computation is a specific kind of manipulation of a specific kind of representation. (People disagree about which representations and manipulations are needed for computation.)
This semantic view of computation, popular as it may be, doesn’t hold up under scrutiny. The main problem is that just about any paradigmatic example of computing system can be defined without positing representations. A digital computer can be programmed to alphabetize meaningless strings of letters. A Turing machine can be defined so as to manipulate meaningless symbols in meaningless ways. And so on.
The traditional alternative to the semantic view is the mapping view, according to which all there is to physical computation is a mapping between a physical and a computational description of a system. According to the mapping view, a physical system computes just in case there is a computational description that maps onto it. The main problem with the mapping view is that it leads to pancomputationalism–the view that everything computes. For just about any physical system is such that a computational description can map onto it. Even sophisticated mapping views, which are augmented by counterfactual, causal, or dispositional bells and whistles, still lead to pancomputationalism. But it doesn’t seem that everything computes–at least, not everything computes in the same sense. (I plan to discuss pancomputationalism in a later post.)
The mechanistic account of computation attempts to give an adequate account of physical computation, which does justice to the practices of the computational sciences, without requiring that computations manipulate representations and without falling into pancomputationalism.
The way I formulate the mechanistic account proceeds in steps. First, I give an account of mechanisms, which are just systems of organized components performing functions. Second, I give an account of the teleological functions of biological systems and artifacts–an account according to which teleological functions are causal contributions to the goals of organisms. Third, I offer a specific account of computational (teleological) functions.
Roughly, a physical system is a computing system just in case it is a mechanism, it performs teleological functions, and its teleological functions include manipulating vehicles in accordance with a rule that is sensitive to differences between different portions of the vehicles. (Of course, the devil is in the detail, which I cannot go into here.) The important points here are that no representations are required for computation (although most computations surely do manipulate representations, and this is perfectly consistent with the mechanistic account), and most systems are excluded from the class of computing systems so pancomputationalism is avoided.
Before concluding this post, I’d like to add that since I started working on the mechanistic account, others have also offered mechanistic accounts of computation (Marcin Milkowski, David M. Kaplan) or accounts that are closely related (Nir Fresco). So the mechanistic account is catching on 🙂