A version of computationalism

I’ve been thinking how best to define computationalism about the mind, while remaining fairly agnostic about how the brain computes. Here is my best attempt to formulate computationalism:

• If a Turing machine with sufficiently large memory simulates the functioning of a normal adult human being with sufficient accuracy, then given an appropriate mapping of inputs and outputs but without any ontological addition of a nonphysical property or part, (a) the simulated body dispositionally will behave like the simulated one at the level of macroscopic observation, and (b) the simulation will exhibit mental states analogous to those the simulated human would have.

The “analogous” in (b) allows the computationalist at least two difference between the mental states of the simulation and the mental states of the simulated. First, we might allow for the possibility that the qualitative features of mental states—the qualia—depend on the exact type of embodiment, so in vivo and in silico versions of the human will have different qualitative states when faced with analogous sensory inputs. Second, we probably should allow for some modest semantic externalism.

The “without any ontological addition” is relevant if one thinks that the laws of nature, or divine dispositions, are such that if a simulation were made, it would gain a soul or some other nonphysical addition. In other words, the qualifier helps to ensure that the simulation would think in virtue of its computational features, rather than in virtue of something being added.

Note that computationalism so defined is not entailed by standard reductive physicalism. For while the standard reductive physicalist is going to accept that a sufficiently accurate simulation will yield (a), they can think that real thought depends on physical features that are not had by the simulation (we could imagine, for instance, that to have qualia you need to have carbon, and merely simulated carbon is not good enough).

Moreover, computationalism so defined is compatible with some nonreductive physicalisms, say ones on which there are biological laws that do not reduce to laws of physics, as long as these biological laws are simulable, and the appropriate simulation will have the right mental states.

In fact, computationalism so defined is compatible with substance dualism, as long as the functioning of the soul is simulable, and the simulation would have the right mental states without itself having to have a soul added to it.

Computationalism defined as above is not the same as functionalism. Functionalism requires a notion of a proper function (even if statistically defined, as in Lewis). No such notion is needed above. Furthermore, the computationalism is not a thesis about every possible mind, but only about human minds. It seems pretty plausible that (perhaps in a world with different laws of nature than ours) it is possible to have a mind whose computational resources exceed those of a Turing machine.