I have a weakness for philosophy of the mind, but I find most of the writing on the topic either impenetrable or laughable. Recently, a good friend who is a philosopher recommended Searle’s book Mind: A Brief Introduction. It is indeed an excellent book. It makes lucid and careful arguments and, gratifying for a non-philosopher, it shows why most influential theories of the mind are wrong. The programme it sets is very modest and meant to delegate matters from philosophy to science as quickly as possible, but more on this later.
Searle is famous, among other things, for the Chinese Room argument, which is meant to clarify that mimicking understanding and having the experience of understanding are not the same thing. I found the argument compelling. The argument is also meant to have a farther reaching consequence, that the mind cannot be (just) a computational process.
The second part of the argument is less convincing, because you cannot in general prove impossibility by example. It’s close to a straw-man fallacy. I think a different argument is needed here and I will try to formulate it. It takes the Church-Turing thesis as its starting point: anything that can be computed can be computed by a Turing machine. If the mind is a computational phenomenon it must be exhibited by an appropriately programmed Turing machine.
If you don’t know what a Turing Machine is, have a look at one such device. It consists of a tape, a read-write head, and a controller (which can be as small as two-state, three-symbol automaton). I take it as obvious that this device cannot experience thought (i.e. consciousness), but let us elaborate for the sake of argument. The subjective experience of thought should come, if it arises at all, from the contents of the tape, the software. But that is not possible because TM computation is a local phenomenon: at any moment the machine is only “aware” of the controller state and the tape contents. The TM is not “aware” of the global contents of the state. Which would mean that the tape experiences thought. But the software on the tape can be a mind only insofar as it works for a particular encoding of the TM, e.g. the set of symbols. So the “seat” of artificial consciousness is not in the hardware nor in the software, but in the relation between them. But a mind is a real concept, and cannot be contingent on an abstract one. A TM and its tape cannot be or have a mind.
Searle doesn’t quite make this point, but he makes a similar one. A computation is defined by the intention to compute. A computer is a thing that is used by someone to compute — just like a tool is an object with an intended function, otherwise it is just stuff or perhaps an artistic artefact. Any physical system, to the extent that it has a state that changes according to laws that are known, can be used to compute. But in the absence of intent it is not a computer, it is simply a physical system. So the reason why mind cannot be explained as a computational phenomenon is that computation presupposes intent, which presupposes a mind. This would be a circular definition.
A computation is a supra-conscious behaviour: it express the (conscious) intent of another mind. For someone who practices and teaches mathematical subjects the distinction between conscious and algorithmic thought is quite clear. A student (but also a mathematician) can carry out a computation (or a proof) by following an algorithm either deterministically (a simple calculation) or heuristically (manipulation of an expression by symbol-pushing to achieve a proof-objective). This activity is not experienced as conscious in the same way that a mathematical activity involving genuine understanding is. There is no a-ha! moment; the quality of it is not intellectual excitement but a vague sense of boredom. However, this activity is not unconscious either in the sense that one is aware of something that is going on and can start it or stop it at will. I think a new term, such as supra-conscious, is required to capture this experience. I think this term also describes the experience of the Chinese Room operator.
What is mind then? I find Searle’s modest proposal acceptable: the mind is a biological phenomenon, a function of the brain. We don’t understand the details of this function, but it is not of a (purely) computational nature. The brain is not (just) a computer, so no computational simulations of the brain will produce a mind.