Metaphysical Naturalism Is a Crude Form of Idealism

Metaphysical naturalism, the view that the hard sciences possess a rightful claim over all other disciplines regarding the explication of the nature of reality, has spread from scientists through the popular culture and even into some quarters of philosophy. One easily forgives the scientist who overestimates the limits of his or her craft and one hardly faults the common person for being overawed by the accomplishments of the scientific enterprise, but philosophers – who ostensibly ought to be aware of the particular demands of metaphysical inquiry – ought not accept these claims so easily. After all, within the confines of modern science one cannot even make claims as to the metaphysical status of scientific theories, such as whether science treats of things in themselves or of a chain of causes conditioned by transcendental categories, because as soon as one takes up such questions, one has moved from the territory of science to that of philosophy. Therefore, the philosopher ought not simply accept the scientific picture of the world as an entirely true picture – though perhaps, to borrow Heidegger's distinction, the philosopher might accept the scientific picture as correct – but neither ought the philosopher dismiss it out of hand simply because it originated in the field of natural science rather than in the field of philosophy. In order to subject this sort of metaphysics to philosophical scrutiny, this essay will focus on an area in which the tension between metaphysical materialism and its opponents is particularly palpable: the question whether the mind is identical with the brain. I will argue that the metaphysical implications of identity theory have not necessarily been thoroughly thought out and lead to a sort of metaphysical dualism which is untenable, or else to the sort of idealism which would require the scientist to give up on his or her status as an empiricist.

To the metaphysical naturalist, science appears to promise fairly complete answers in most of the areas it has applied itself; however, the explanation of the mind in naturalistic terms is notoriously difficult, and might be seen as the last holdout for the opponents of materialism. As J. J. C. Smart puts it: “There does seem to be, so far as science is concerned, nothing in the world but increasingly complex arrangements of physical constituents. All except for one place: in consciousness.”(1) However, one must note that the mind ought not be considered one item (among a determinate number of other items) that resists – at the outset, at least – scientific explanation; rather, the activity of the mind functions as a necessary prerequisite for the scientific explanation of anything at all—scientific inquiry as such is a particular kind of mental process. So the optimism that science has explained, say, 99% of things in the universe and will therefore probably explain the other 1% that includes the mind overlooks the constitutive role mind plays in the scientific construction of the universe. It would be a mistake to suppose that the mind will be eventually explained just as scientists have explained everything else for the obvious reason that scientific inquiry is bound in a very peculiar fashion to the workings of the mind; the activity of the mind cannot be extirpated from the activity of scientific inquiry in a way that would allow mental activity to ever become a mere object of investigation. This does not mean that the mind cannot be explained in a naturalistic way, and so we can proceed through Smart's argument without error as long as we remain aware of the peculiar relation of the mind to scientific explanation and avoid the unreflective talk of “nomological danglers”.

Identity theory depends upon the distinction between the “is” of correlation and the “is” of identity; identity theorists do not wish merely to argue that mental states are correlated with brain states, but that mental states are identical with brain states. The weaker claim that whenever a person has a mental state, that person also has a brain state – an entirely reasonable claim – does not go far enough for Smart; the mental state must be identical with the brain state. To put it succinctly: “Sensations are nothing over and above brain processes.”(2)

As Smart notes, this immediately calls forth the obvious problem that one can talk about mental processes without knowing about brain processes, and so he must distinguish between what the common person means by “mental process” and what mental processes actually are. In fact, the identity theorist must say that what the common person actually refers to is a brain process insofar as he or she refers to anything at all. Both U. T. Place and Smart refer to the way in which lightning, rather than being thrown down from the heavens by Zeus as an ancient Greek might have thought, is (in the sense of identity, not merely correlation) the discharge of electricity; the way in which heat must be identified as molecular motion; or some other natural phenomena which readily admits to reduction to a scientific model. U. T. Place declares that the phrase “'consciousness is a process in the brain' in my view is neither self-contradictory nor self evident; it is a reasonable scientific hypothesis, in the way that the statement 'Lightning is a motion of electric charges' is a reasonable scientific hypothesis.”(3) Likewise, Smart remarks:

When I say that a sensation is a brain process or that lightning is an electrical discharge, I am using “is” in the sense of strict identity (just as in the – in this case necessary – proposition “7 is identical with the smallest prime number greater than 5.”) When I say that a sensation is a brain process or that lightning is an electrical discharge I do not mean just that the sensation is somehow spatially or temporally continuous with the brain process or that lightning is just spatially or temporally continuous with the discharge.

Both Place and Smart base their identity theory in the analogy that just as natural phenomena appear one way, scientists have actually discovered them to be something else entirely, and both presume that natural phenomena can be reduced to the corresponding scientific explanation, leaving nothing left over. Therefore, while one might agree that one aspect of lightning might be an electrical discharge, or that one aspect of mental activity might be the functioning of the brain, this does not go far enough for the identity theorists; just as lightning is electrical discharge and no more, so mental processes are brain functions and no more. At this point, one can begin to see the outlines of a wider metaphysical view of the world surfacing, which, under further analysis, might turn out to be quite suspect.

If identity theorists wish to offer the scientific model of the universe as an exhaustive explanation of the world,(4) then they propose a dualistic ontology which posits that things do not appear in everyday life in the way that they exist in reality—which signifies nothing else than a sort of revival of Kant's distinction between phenomenon and noumenon. Thus, the common man might say, “my feelings toward my pet goldfish sure don't feel like neurons firing in my head”, but who is he to know? After all, just as the true nature of lightning cannot be conveyed through the perceptual experience of lightning, neither does the apperception of affection reveal the ontological basis of mental states. This means that what appears can be devoid of what truly exists, that phenomenon can be devoid of noumenon. Thus, one can find within the ordinary apperceptual experience of affection absolutely nothing about the neurological process that supposedly constitutes the reality of the experience (remember, we aren't talking about physical processes which accompany mental processes, but physical processes and nothing else).

Ought we to consider the division between what appears and what exists absolute? We have established that we appercieve mental states without any hint of their supposed “true nature”, but perhaps mental states alone do not convey their true nature, perhaps the true nature of externally existing things does become accessible through their appearances. Taking Place's example of a cloud, we might say that although the ancients might have thought of clouds as fairly solid objects, one finds on closer examination – through the help of a hot air balloon – that clouds are not solid at all, but droplets of water. In this example, the true nature of the cloud gets revealed through the perceptual experience of clouds, and humans were formerly deceived (for the purposes of our story) because they didn't have the requisite technology to get the needed vantage point to reveal the true nature of the clouds. However a few problems present themselves. In the first case, why ought the closer appearance of clouds be privileged over the way they appear from the ground? What reason do we have for regarding the more accurate view of clouds as the one from the air? One answer that might be given: things appear most fully to human beings “within arm's reach”. I am not entirely satisfied by this answer, as I think a counter-argument might be made that the way in which clouds appear in the usual course of human activities ought to be considered the truer view; however, for the purpose of this discussion, we can accept the “arm's reach” explanation.

The second, more significant problem regarding the cloud example occurs when one says that the true nature of the cloud consists not in the small droplets I might catch in my fingers from within the hot air balloon (and therefore, the droplets I can feel and see), but in the accumulation of H20, suspended in the air by certain pressures, reacting to gravity in certain ways, and so on. Nothing in my perceptual experience of the water droplets forming on my hand gives me anything like the molecule H20, and if one wishes to say that the true nature of water can be exhausted in that molecular form, then the true nature of the cloud again exists nowhere in the perceptual experience of it. This suspicion only gets confirmed more thoroughly if we consider again the favorite example of identity theorists: lightning. If, while I am gliding my hand through the cloud before me while riding in my hot air balloon and trying in vain to somehow perceive two hydrogen atoms and one oxygen atom, my hot air balloon gets struck by lightning, then not only do I not perceive lightning any better than from a distance – indeed, it seems as though I might have more clear view from a distance – but I don't see anything like an electrical discharge; instead I see a blinding flash, hear a crash, perhaps smell the fabric of my hot air balloon burning, and so on. Neither the perceptual experience of the cloud nor that of lightning gives me anything like H20 or electricity, and so one would expect to find this true of all natural phenomena. Indeed, if we were to get down to the basic constituents of the physical universe, we find quantum theory proposing things which cannot be observed (in principle) as basic to reality—and even claiming that the whole of things within space and time are held in being by super-spatial and super-temporal quantum strings vibrating. If this turns out to be true, the universe as a whole would have its true reality in something that can be neither perceived nor even imagined, but only modeled mathematically. Therefore, I think it safe to say that the identity theorist's metaphysics posits an absolute divide between appearances and reality, meaning that reality cannot become available through perception.

Though Place and Smart might maintain an absolute division between phenomenon and noumenon, one sees that they cannot regard the noumenal (as Kant did) as absolutely beyond knowledge, but rather precisely as that in which the true natures of things become known. This brings us to a peculiar turn: the kind of materialism which the identity theorists advocate – wherein the universe as it shows up in the hard sciences exhausts the whole of its reality – turns out to be a kind of idealism, in that reality is constituted by ideal models which cannot be given in perception, and while transcendental idealism does not regard either the pole of appearances or the pole of reality as more real than its opposite, identity theorists must deny any ontological status to appearance and instead maintain that scientific constructions exhaust the whole of the real. This is the full metaphysical consequence of declaring that lightning is electronic discharge and nothing else, that water is H20 and nothing else, and that mental processes are brain processes and nothing else. However, the identity theorist might protest that while hydrogen atoms cannot be perceived, brain processes can be perceived through the use of mental imaging equipment. In this case we must note that even if mental processes could be observed, the more basic (and therefore more real, on the materialist view) physical constituents still stand beyond the possibility of anything other than mathematical modeling. Secondly, and more importantly if we wish to maintain an absolute distinction between the phenomenal and noumenal, one does not really perceive brain processes when one views a CAT scan any more than one observes a duck when one sees the word “duck.” The image that the brain scan reveals stands in for the brain process; it represents it in the same way way atomic force microscopy generates an image that represents an atom. A process itself cannot be given in strictly sensuous experience any more than a cause could be (as Hume famously observed).

Although one might find it ironic that a philosophical position which purports to be empirical in fact entails a radically idealistic ontology that denies the reality of sensuous perception per se, this does not yet constitute an argument against identity theory. I would suppose that Smart or Place might be willing to give up on the strict claim that natural phenomena must be identified with the scientific explanation of that phenomena and nothing over and above that, since it leads rather obviously to the idealism I have been expounding, but of course I can't speak for them. And this would require them to give up identity theory. So I will end my formal argument here and – as I don't have space to make another rigorous argument – instead suggest some reasons why one should be very suspicious of identity theory's tacit ontology.

In order to convince a person that their perceptual experience can never convey reality, but instead can only stand in for ideal models beyond any possible perception, one would need – as the “man on the street” might say to the enthusiastic identity theorist – a damn good argument. In fact, I am suspicious that any argument could convince anyone that the way in which we see and encounter the world around us ought to be considered an illusion; the sheer force of the world's truth presses in through perception over against any attempt to deny it—indeed, the philosopher might need a good deal of peace and quiet to deny the reality of what threatens to distract him from his studies. Neither Smart nor Place offer a convincing argument to consider appearances void of reality, they simply assume this to be the case.

One way to disprove identity theory might consist in a phenomenological investigation which would lay out precisely how science arises as a function of the consciousness, and would lay out the ways in which this sort of consciousness depends on the “life-world” (as Husserl called it). At this point, one could examine whether or not science has – by virtue of the type of consciousness it is – the capacity to make metaphysical claims about the world, and one would perhaps demonstrate from this that science necessarily deals with constructs which have a lesser claim to reality than, for example, philosophical claims. In this way, one could show that metaphysical naturalism arises from a misunderstanding of the basic nature of science. Of course, fleshing out these arguments would have to take place in a further essay.

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1.J. J. C. Smart, p. 60.
2. Smart, 62.
3. Place, 56.
4. As consistently as possible, I will use the term “universe” to refer to the scientific model of the world used by physics, and “world” to refer to the lived-in phenomenal world—by which I mean nothing more than the world as it ordinarily shows up for us in everyday life.