However I'm now beginning to suspect that there might be more than a few problems with functionalism. For starters, functional states are often defined as being those that are "relevantly similar" to an imagined paradigm case - thus, a Martian who screamed and recoiled when we punched might be said to be in pain, but one that laughed and clapped its hands (tentacles?) probably wouldn't. This is fine up to a point, especially in seemingly clear-cut cases like the above, but what should we say when we're faced with the inevitable borderline case?
Whether or not fish can feel pain seems to be a case like this. Research into fish pain behaviour is contentious - whilst fish exhibit apparent pain behaviour, they have only recently been shown to exhibit more complex pain avoidance behaviour that might be thought essential to pain. The problem is not just a lack of evidence either, there's a more fundamental lack of clarity about how exactly we should define the functional role of pain, or indeed any other mental state.
Having said that, the problem isn't limited to the functionalist account of mental states. Biological species appear to form vague natural kinds, a problem which has motivated the idea of homeostatic property cluster kinds, categories of kinds that share some, but not all, of their properties. So we maybe we could say that functional kinds, such as pain, are a category of HPC kinds. That still wouldn't necessarily give us a straight answer in genuine border-line cases, but at least we'd have good reason to think functional roles might sometimes pick out genuine kinds (albeit perhaps not natural kinds).
The problems don't stop there though. By arguing that it entails a radical form of cognitive extension, Mark Sprevak has pushed functionalism to its logical extreme. If he is correct then being a functionalist would commit you to apparently absurd conclusions,1 such as that the entire contents of the Dictionary of Philosophy sitting on my desk form part of my cognitive system, or that my capacity for mental arithmetic is bounded only by my access to electronic computing power. I think there might be a way for functionalism to avoid the full force of this argument, but it comes with its own problems and costs.
Essentially what the functionalist needs to do is to stop talking about cognition and mental states as though they were one kind of thing. They're not, and rather than lumping memory, personality, beliefs and so on into one unitary framework, we need to look at giving finer-grained functional descriptions in each case. This might even mean getting rid of some mental states, such as belief, or at least admitting that they're more complex than we first thought. This approach will still entail some degree of cognitive extension, but hopefully in a more subtle and intuitive way. So whilst it might not be true that the contents of the Dictionary are part of my 'cognitive system', they may nonetheless form part of a belief-like system, albeit one that functions differently to my regular belief system.
Would this still be functionalism? In a sense yes, because it would maintain a degree of multiple realisability, only at a more fine-grained level. So a Martian with a silicon brain might have beliefs, but equally they might have something more akin to the belief-like system that is constituted by me-and-the-Dictionary. The problem with functionalism is that it tends to reify our folk intuitions about mental states, and we need to remember that these might not be entirely accurate. I suppose I'm beginning to lean towards a form of eliminativism, although I still think that there's room for an instrumentalist account of functional roles.
1. I say "apparently" because I'm not entirely convinced that one shouldn't just bite the bullet and accept these conclusions. That's probably a post for another day though.
