Stephen Law has new arguments against physicalism (which is, approximately, the view that the account of the world given by physics is good enough to explain everything). He thinks conscious experience can’t be dealt with by physics alone. There is a well-established family of anti-physicalist arguments supporting this view which are based on conceivability; Law adds new cousins to that family, ones which draw on inconceivability and are, he thinks, less vulnerable to some of the counter-arguments brought against the established versions.

What is the argument from conceivability? Law helpfully summarises several versions (his exposition is commendably clear and careful throughout) including the zombie twin argument we’ve often discussed here; but let’s take a classic one about the supposed identity of pain and the firing of C-fibres, a kind of nerve. It goes like this…

1. Pain without C-fibre firing is conceivable
2. Conceivability entails metaphysical possibility (at least in this case)
3. The metaphysical possibility of pain without C-fibre firing entails ?that pain is not identical with C-fibre firing.
C. Pain is not identical with C-fibre firing

(It’s good to see the old traditional C-fibre example still being quoted. It reminds me of long-gone undergraduate days when some luckless fellow student in a tutorial read an essay citing the example of how things look yellow to people with jaundice. Myles Burnyeat, the tutor, gave an erudite history of this jaundice example, tracking it back from the twentieth century to the sixteenth, through mediaeval scholastics, Sextus Empiricus (probably), and many ancient authors. You have joined, he remarked, a long tradition of philosophers who have quoted that example for thousands of years without any of them ever bothering to find out that it is, in fact, completely false. People with jaundice have yellowish skin, but their vision is normal. Of course the inaccuracy of examples about C-fibres and jaundice does not in itself invalidate the philosophical arguments, a point Burnyeat would have conceded with gritted teeth.)

I have a bit of a problem with the notion of metaphysical possibility. Law says that something being conceivable means no incoherence arises when we suppose it, which is fine; but I take it that the different flavours of conceivability/possibility arise from different sets of rules. So something is physically conceivable so long as it doesn’t contradict the laws of physics. A five-kilometre cube of titanium at the North Pole is not something that any plausible set of circumstances is going to give rise to, but nothing about it conflicts with physics, so it’s conceivable.

I’m comfortable, therefore, with physical conceivability, and with logical conceivability, because pretty decent (if not quite perfect) sets of rules for both fields have been set out for us. But what are the laws of metaphysics that would ground the idea of metaphysical conceivability or equally, metaphysical possibility? I’m not sure how many candidates for such laws (other than ones that are already laws of physics, logic, or maths) I can come up with, and I know of no attempt to set them out systematically (a book opportunity for a bold metaphysician there, perhaps). But this is not a show-stopper so long as it is reasonably clear in each case what kind of metaphysical rules we hold ourselves not to be violating.

Conceivability arguments of this kind do help clarify an intuitive feeling that physical events are just not the sort of thing that could also be subjective experiences, firming things up for those who believe in them and sportingly providing a proper target for physicalists.

So what is the new argument? Law begins by noting that in some cases appearance and reality can separate, while in others they cannot. So a substance that appears just like gold, but does not have the right atomic number, is not gold: we could call it fool’s gold.  A medical case where the skin was yellowish but the underlying condition was not jaundice might be fool’s jaundice (jaundice again, but here used unimpeachably). However, can there be fool’s red?  If we’re talking of a red experience it seems not: something that seems red is indeed a red experience whatever underlies it. More strongly still, it seems that the idea of fool’s pain is inconceivable. If what you’re experiencing seems to be pain, then it is pain.

Is that right? There’s evidently something in it, but what is to stop us believing ourselves to be in pain when we’re not? Hypochondriacs may well do that very thing. Law, I suppose, would say that a mistaken belief isn’t enough; there has to be the actual experience of pain. That begins to look as if he’s  in danger of begging the question; if we specify that there’s a real experience of pain, then it’s inconceivable it isn’t real pain? But I think the notions of mistaken pain beliefs and the putative fool’s pain are sufficiently distinct.

The inconceivability argument goes on to suggest that if fool’s pain is inconceivable, but we can conceive of C-fibre firing without pain, then C-fibre firing cannot be identical with pain. Clearly the same argument would apply for various mental experiences other than pain, and for any proposed physical correlate of pain.

Law rebuts explicitly arguments that this is nothing new, or merely a trivial variant on the old argument. I’m happy enough to take it as a handy new argument, worth having in itself; but Law also argues that in some cases it stands up against counter-arguments better than the old one. Notably he mentions an argument by Loar.  This offers an alternative explanation for the conceivability of pain in the absence of C-fibre firing: experience and concepts such as C-fibre firing are dealt with in quite different parts of the brain, and our ability to conceive of one without the other is therefore just a matter if human psychology, from which no deep metaphysical conclusions can be drawn. Law argues that even if Loar’s argument or a similar one is accepted, we still run up against the problem that conceiving of pain without C-fibre firing, we are conceiving of fool’s pain, which the new argument has established in inconceivable.

The case is well made and I think Law is right to claim he has hit on a new and useful argument. Am I convinced? Not really; but my disbelief stems from a more fundamental doubt about whether conceivability and inconceivability can actually tell us about the real world, or merely about our own mental powers.

Perhaps we can look at it in terms of possible worlds. It seems to me that Law’s argument, like the older ones, establishes that we can separate C-fibre firing and pain conceptually; that there are in fact possible worlds in which pain is not C-fibre firing. But I don’t care. I don’t require the identity of pain and C-fibre firing to be true a priori; I’m happy for it to be true only in this world, as an empirical, scientific matter. Of course this opens a whole range of new cans of worms (about which kinds of identity are necessary, for example) whose contents I am not eager to ingest at the moment.

Still, if you’re interested in the topic I commend the draft paper to your attention.