The best argument for functionalism* in my opinion is that there aren’t really any good alternatives. If mental state kinds aren’t functional kinds, they’d presumably have to be neuroscientific kinds. But if that’s right, then we can already know now aliens without neurons aren’t conscious. Which seems wild to me: how can we possibly know if aliens are conscious till we meet them, and observe their behavior and how it depends on what goes on inside them? And surely once we do meet them, no one is going to say “oh consciousness is this sort of neurobiological property, we looked in their head with our scanner and they have no neurons, problem solved, we know they aren’t conscious. People seem to want there to be some intermediate view that says “oh of course there might be conscious aliens with different biology, we just mean to rule out weird functional duplicates of humans like a robot controlled by radio signals running the same program as human**”, but it’s really unclear how to do that in a principled way. (And I suspect the root of the desire to do so is a sort of primitive sense that living matter can have feelings but dead matter can’t, which I think people would consciously disavow if they understood it was driving their views)
*There’s an incredibly technical complication here about the fact that “functionalism” is usually defined in opposition to mind-body dualism, but in the current context it makes more sense to classify certain forms of dualism as functionalist, since they agree with functionalism about what guarantees something is conscious in the actual world. But I’m going to ignore it because I don’t think I can explain it to non-philosophers quickly and easily.
The best argument for functionalism* in my opinion is that there aren’t really any good alternatives. If mental state kinds aren’t functional kinds, they’d presumably have to be neuroscientific kinds. But if that’s right, then we can already know now aliens without neurons aren’t conscious. Which seems wild to me: how can we possibly know if aliens are conscious till we meet them, and observe their behavior and how it depends on what goes on inside them? And surely once we do meet them, no one is going to say “oh consciousness is this sort of neurobiological property, we looked in their head with our scanner and they have no neurons, problem solved, we know they aren’t conscious. People seem to want there to be some intermediate view that says “oh of course there might be conscious aliens with different biology, we just mean to rule out weird functional duplicates of humans like a robot controlled by radio signals running the same program as human**”, but it’s really unclear how to do that in a principled way. (And I suspect the root of the desire to do so is a sort of primitive sense that living matter can have feelings but dead matter can’t, which I think people would consciously disavow if they understood it was driving their views)
*There’s an incredibly technical complication here about the fact that “functionalism” is usually defined in opposition to mind-body dualism, but in the current context it makes more sense to classify certain forms of dualism as functionalist, since they agree with functionalism about what guarantees something is conscious in the actual world. But I’m going to ignore it because I don’t think I can explain it to non-philosophers quickly and easily.
**https://en.wikipedia.org/wiki/China_brain