Thomas Nagel replies in the pages of New York Review of Books (8 June 2017) to one Roy Black, a professor of bioengineering:
The mind-body problem that exercises both Daniel Dennett and me is a problem about what experience is, not how it is caused. The difficulty is that conscious experience has an essentially subjective character—what it is like for its subject, from the inside—that purely physical processes do not share. Physical concepts describe the world as it is in itself, and not for any conscious subject. That includes dark energy, the strong force, and the development of an organism from the egg, to cite Black’s examples. But if subjective experience is not an illusion, the real world includes more than can be described in this way.
I agree with Black that “we need to determine what ‘thing,’ what activity of neurons beyond activating other neurons, was amplified to the point that consciousness arose.” But I believe this will require that we attribute to neurons, and perhaps to still more basic physical things and processes, some properties that in the right combination are capable of constituting subjects of experience like ourselves, to whom sunsets and chocolate and violins look and taste and sound as they do. These, if they are ever discovered, will not be physical properties, because physical properties, however sophisticated and complex, characterize only the order of the world extended in space and time, not how things appear from any particular point of view.
The problem might be condensed into an aporetic triad (my formulation, not Nagel’s):
1) Conscious experience is not an illusion.
2) Conscious experience has an essentially subjective character that purely physical processes do not and cannot share.
3) The only acceptable explanation of conscious experience is in terms of physical properties alone.
Take a little time to savor this problem. Note first that the three propositions are collectively inconsistent: they cannot all be true. Any two limbs entail the negation of the remaining one. Note second that each limb exerts a strong pull on our acceptance. But we cannot accept them all because they are logically incompatible. Individually plausible to a high degree, but collectively inconsistent.
Which proposition should we reject? Dennett, biting the bullet, rejects (1). But that's a lunatic solution as Professor Black seems to appreciate, though he puts the point more politely. When I call Dennett a sophist, as I have elsewhere, I am not (mainly) abusing him; I am underscoring what is obvious, namely, that the smell of cooked onions, for example, is a genuine datum of experience, and that such phenomenological data trump scientistic theories. (1) has no chance of being true.
Sophistry aside, we either reject (2) or we reject (3). Nagel and I accept (1) and (2) and reject (3). Black, and others of the scientistic stripe, accept (1) and (3) and reject (2).
I appreciate the appeal of the naturalistic-scientistic worldview and I don't dismiss it in the way I dismiss eliminativism about the mental. Here is my brief for the worldview in question:
Look, there is just one world, this physical world, and we are physical parts of it including all of our precious thoughts, moods, and sensations. If you are serious about explaining consciousness, then you have to explain it the way you explain everything else: in terms of our best natural science. With the progress of science over the centuries, more and more of what hitherto was thought inexplicable scientifically has been explained. The trend is clear: science is increasingly de-mystifying the world, and it is a good induction that one day it will have wholly de-mystified it and will have cut off every obscurantist escape route into the Cloud Cuckoo Land of religion/superstition.
It is essential to see, however, that this naturalistic-scientistic worldview is precisely that, a worldview, and therefore just another philosophy. This is what makes it scientistic as opposed to scientific. Scientism is not science, but philosophy. Scientism is the epistemology of metaphysical naturalism, so-labelled to distinguish it from ethical naturalism, where metaphysical naturalism is not science but ontology. (To save keystrokes I will now drop the qualifier ‘metaphysical.’) Naturalism is the view that the whole of reality is exhausted by the physical, by space-time and its contents. No natural science can prove that reality is exhausted by the physical, and no natural science can prove that all and only the naturally-scientifically knowable is knowable.
But it is not irrational to be a naturalist and a scientisticist — to coin an ugly word for an ugly thing — in the way that it is irrational to be an eliminativist. It is also not irrational to reject naturalism and scientism.
And so the strife of systems will continue. People like me and Nagel will continue to insist that qualia, intentionality, conscience, normativity, reason, truth and other things cannot be explained naturalistically. Those on the other side will keep trying. Let them continue, with vigor. The more they fail, the better we look.
Do those on our side have a hidden religious agenda? Some do. But Nagel doesn't. He is just convinced that the naturalist project doesn't work. Nagel rejects theism, and he says somewhere that he very much does not want it to be the case that religion is true.
Nagel, then, has no religious agenda. But this did not stop numerous prominent, but viciously leftist, academics from attacking him after he published Mind and Cosmos on the ground that he was giving aid and comfort to theism and religion generally. See the following articles of mine:
Should Nagel's Book be on the Philosophical Index Librorum Prohibitorum?