I had an email exchange with Philip Calcott recently about dualism; here’s an edited version. (Favouring my bits of the dialogue, of course!)

Philip: The main issue that puzzles me regarding consciousness is why most people in the field are so wedded to physicalism, and why substance dualism is so out of favour. It seems to me that there is indeed a huge explanatory gap – how can any physical process explain this extraordinary (and completely unexpected on physicalism) “thing” that is conscious experience?

It seems to me that there are three sorts of gaps in our knowledge:

1. I don’t know the answer to that, but others do. Just let me just google it (the exact height of Everest might be an example)
2. No one yet knows the answer to that, but we have a path towards finding the answer, and we are confident that we will discover the answer, and that this answer lies within the realm of physics (the mechanism behind high temperature superconductivity might be an example here)
3. No one can even lay out a path towards discovering the answer to this problem (consciousness)

Chalmers seems to classify consciousness as a “class 3 ignorance” problem (along the lines above). He then adopts a panpsychism approach to solve this. We have a fundamental property of nature that exhibits itself only through consciousness, and it is impossible to detect its interaction with the rest of physics in any way. How is this different from Descartes’ Soul? Basically Chalmers has produced something he claims to be still physical – but which is effectively identical to a non-physical entity.

So, why is dualism so unpopular?

I think there are two reasons. The first is not an explicit philosophical point, but more a matter of the intellectual background. In theory there are many possible versions of dualism, but what people usually want to reject when they reject it is traditional religion and traditional ideas about spirits and ghosts. A lot of people have strong feelings about this for personal or historical reasons that give an edge to their views. I suspect, for example, that this might be why Dan Dennett gives Descartes more of a beating over dualism than, in my opinion at least, he really deserves.

Second, though, dualism just doesn’t work very well. Nobody has much to offer by way of explaining how the second world or the second substance might work (certainly nothing remotely comparable to the well-developed and comprehensive account given by physics). If we could make predictions and do some maths about spirits or the second world, things would look better; as it is, it looks as if dualism just consigns the difficult issues to another world where it’s sort of presumed no explanations are required. Then again, if we could do the maths, why would we call it dualism rather than an extension of the physical, monist story?

That leads us on to the other bad problem, of how the two substances or worlds interact, one that has been a conspicuous difficulty since Descartes. We can take the view that they don’t really interact causally but perhaps run alongside each other in harmony, as Leibniz suggested; but then there seems to be little point in talking about the second world, as it explains nothing that happens and none of what we do or say. This is quite implausible to me, too, if we’re thinking particularly of subjective experience or qualia. When I am looking at a red apple, it seems to me that every bit of my subjective experience of the colour might influence my decision about whether to pick up the apple or not. Nothing in my mental world seems to be sealed off from my behaviour.

If we think there is causal interaction, then again we seem to be looking for an extension of monist physics rather than a dualism.

Yet it won’t quite do, will it, to say that the physics is all there is to it?

My view is that in fact what’s going on is that we are addressing a question which physics cannot explain, not because physics is faulty or inadequate, but because the question is outside its scope. In terms of physics, we’ve got a type 3 problem; in terms of metaphysics, I hope it’s type 2, though there are some rather discouraging arguments that suggest things are worse than that.

I think the element of mystery in conscious experience is in fact its particularity, its actual reality. All the general features can be explained at a theoretical level by physics, but not why this specific experience is real and being had by me. This is part of a more general mystery of reality, including the questions of why the world is like this in particular and not like something else, or like nothing. We try to naturalise these questions, typically by suggesting that reality is essentially historical, that things are like this because they were previously like that, so that the ultimate explanations lie in the origin of the cosmos, but I don’t think that strategy works very well.

There only seem to be two styles of explanation available here. One is the purely rational kind of reasoning you get in maths. The other is empirical observation. Neither is any good in this context; empirical explanations simply defer the issue backwards by explaining things as they are in terms of things as they once were. There’s no end to that deferral. A priori logical reasoning, on the other hand, delivers only eternal truths, whereas the whole point about reality and my experience is that it isn’t fixed and eternal; it could have been otherwise. People like Stephen Hawking try to deploy both methods, using empirical science to defer the ultimate answer back in time to a misty primordial period, a hypothetical land created by heroic backward extrapolation, where it is somehow meant to turn into a mathematical issue, but even if you could make that work I think it would be unsatisfying as an explanation of the nature of my experience here and now.

I conclude that to deal with this properly we really need a different way of thinking. I fear it might be that all we can do is contemplate the matter and hope pre- or post-theoretical enlightenment dawns, in a sort of Taoist way; but I continue to hope that eventually that one weird trick of metaphysical argument that cracks the issue will occur to someone, because like anyone brought up in the western tradition I really want to get it all back to territory where we can write out the rules and even do some maths!

As I’ve said, this all raises another question, namely why we bother about monism versus dualism at all. Most people realise that there is no single account of the world that covers everything. Besides concrete physical objects we have to consider the abstract entities; those dealt with in maths, for example, and many other fields. Any system of metaphysics which isn’t intolerably flat and limited is going to have some features that would entitle us to call it at least loosely dualist. On the other hand, everything is part of the cosmos, broadly understood, and everything is in some way related to the other contents of those cosmos. So we can equally say that any sufficiently comprehensive system can, at least loosely, be described as monist too; in the end there is only one world. Any reasonable theory will be a bit dualist and a bit monist in some respects.

That being so, the pure metaphysical question of monism versus dualism begins to look rather academic, more about nomenclature than substance. The real interest is in whether your dualism or your monism is any good as an elegant and effective explanation. In that competition materialism, which we tend to call monist, just looks to be an awfully long way ahead.