Frequent correspondent Dianelos Georgoudis recently responded to my request that he present three conceptual problems with metaphysical naturalism. I had planned to address all three in a single post, but the issues are tangled and multifaceted, so I really only managed to address his first one—and this is still a very long post. The other points will have to wait until later.

I think, as is so often the case, one source of our disagreement is that we have different understandings of the terms. Metaphysical naturalism (MN) is a hard term to define precisely. The metaphysical naturalist (hereafter, just “naturalist”) is most definitely not committed to the view that current science offers a complete and satisfactory description of reality. Clearly, it doesn’t. Hence, if quantum mechanics and relativity clash at some level, or if QM seems to imply irresolvable paradoxes, this is a problem for physicists—or rather, perhaps, philosophers of physics—but not for MN or the naturalist qua naturalist. The naturalist affirms that substantial (non-abstract) reality is in some sense physical or natural, that is, that it is constituted exclusively of entities that act and are acted upon in accordance with regular, impersonal, and universal laws. The naturalist is not committed to the view that we now have an exhaustive and accurate understanding of those entities or the laws that govern them. On the contrary, our understanding of the universe and its constituents is (and may always be) a work in progress.

At bottom, I think that what really motivates MN is the idea that nature is a closed system. That is, that whatever happens in the natural world is explicable in terms of natural entities, forces, and processes, and that there is no need to invoke supernatural beings, powers, or occurrences, such as gods, souls, or miracles to account for anything that happens in the universe. So, a naturalist might not really be averse to the idea of impersonal supernatural entities, such as Platonic ideas, so long as those purported entities are sequestered within “their own realm” and cannot act upon or influence the phenomena of the physical universe. In short, naturalists endorse the vision of the first philosophers of the Western tradition, the Milesians of the 6th Century B.C.E.: That the arche of things is to be found in physis itself, that is, that the origin, primordial stuff, and underlying principles of natural things is to be found in nature, not in myths about gods, ghosts, and gobbledygook.

Why would anyone accept MN? Speaking personally, I am extremely suspicious of any sort of positive assertions about “ultimate reality.” I think when we venture in that direction we are in extreme danger of having our thinking become perversely “dialectical” in Kant’s sense, that is, we begin to use concepts that have meaning in empirically constrained contexts, and try to apply them where there are no such constraints. The consequence is that we quickly fly off into conceptual cloud-cuckoo-land where nobody knows what he is talking about and philosophers become fools. For instance, I have no idea at all what it could mean to say, as some religious philosophers do, that some putative ultimate reality is more objectively probable than another. The reason is that it is meaningful and useful to speak of the objective probability of things or events where we have some sort of experience or theory to guide and constrain us, but when we have prescinded our probability judgments from any such background or context, such judgments can only be pretentious expressions of ignorance or bias.

Therefore, I am a naturalist by default. I know that physical entities exist. I know that science has made enormous progress with theories that postulate only natural entities, and that over the history of science supernatural hypotheses have been ruthlessly driven out in favor of naturalistic ones. I do not know that supernatural entities exist, and it is my judgment that the purported evidence for their existence ranges from the shoddy to the risible. Natural theology is a failed research program and, as for ghosts, demons, and supernatural bugaboos in general, for over thirty years the Skeptical Inquirer has had good fun debunking those claims. Therefore, if forced to place my bets about “ultimate reality” I’ll wager that it is physical, and I shall continue to look for physical explanations of physical phenomena. Also, I put the burden of proof on anyone who says that there is a problem with taking reality to be physical. Does Mr. Georgoudis meet that burden?

His first objection to MN is what he calls “the problem of consciousness”:

“Consciousness is a scientifically unnecessary concept, because it does not refer to something observable, nor is the hypothesis that it exists necessary for explaining anything observable. Thus consciousness lies beyond the scientific field of investigation. According to scientific naturalism nothing exists but the objects of science, which implies the non-existence of consciousness. But consciousness clearly does exist, and cannot be construed to be an illusory concept.”

What is consciousness? Nobody can define it and the whole confused notion is a conceptual minefield. We have to be very careful how we speak or we get inextricably mired in a quagmire of obfuscation. First of all, consciousness is not a thing, we must not reify it and try to think of it as some sort of concrete being or entity (I think such reification is at the core of Cartesian dualism). Consciousness is not a ghost in the machine, or a homunculus sitting inside of us watching and directing all that we do, as in the hilarious bit from Woody Allen’s Everything You Always Wanted to Know about Sex. We therefore do not expect that consciousness will be observable in the same way that a horse is, or even in the same way that a chromosome is. “Consciousness” is a term that, in ordinary usage, encompasses a very large number of phenomena, states, and processes. Phenomena like feeling, states like self-awareness, and processes like thinking through a problem all occur consciously, or, at least, some aspects of them occur consciously. Can any of these multifarious items be observed or detected in any sense?

Of course. What could be more observable? We enact states of consciousness constantly in our own first-person cases, and we have all sorts of ways of accessing other people’s conscious states indirectly. Is the supposed problem the fact that we can only observe other people’s conscious states indirectly, rather than immediately? I cannot literally feel your pain, but I have all sorts of ways of knowing when you are in pain (e.g., your report through gritted teeth that you are in pain). In fact, I can get quite a bit of detailed information about just what kind of pain you have. The fact that pain detection is indirect doesn’t mean that pain is not an appropriate object for scientific study. Most of the items that science studies are detected indirectly (e.g., neutrinos). It is a common mistake (often committed by creationists, BTW) to think that science deals with observables. What science requires is not direct observability but that we have reliable empirical access to phenomena, and that access is often quite mediated and roundabout.

Mr. Georgoudis says that consciousness is a “scientifically unnecessary concept.” What does this mean? Does it mean that the phenomena we explain by that concept could be explained more economically by other concepts, or that scientific inquiry has invalidated that concept, or that the concept reduces to a more basic concept? Of course, the concept of consciousness is logically unnecessary, but so are the past and an external world. The phenomena we explain in terms of consciousness (except in our own first-person case) could conceivably be due to unconscious causes. Likewise, our apparent perceptions of external objects could co

nceivably be due to delusions induced by a Cartesian evil genius. Similarly, there is no contradiction in supposing that everything, including every apparent trace of a past, could have been created ten seconds ago. It is conceivable that my friend’s expressions of outrage or empathy are not due to feelings of outrage or empathy, but are instead the programmed output of a cleverly constructed but unconscious android. Hence, the famous philosophical problem of other minds. But that the nonexistence of something is a logical possibility does not mean that it is something that should be neglected by science or common sense. You might be nothing but a brain in a vat, but you still had better get your doctor to check that suspicious looking mole.

Are there any episodes from the history of science where inferences to the best explanation have led to the postulation of conscious phenomena, states, or processes? Sure there are. Plenty of them. In their terrific book Baboon Metaphysics, Dorothy L. Cheney and Robert M. Seyfarth give some quite fascinating examples (pp. 7-9). In the early heyday of behaviorism, psychologists Edward C. Tolman and Otto L. Tinklepaugh (real name; bet he had a tough time in junior high) did some studies of monkeys that challenged the behaviorist tenet that mental states are private and unmeasurable and so not amenable to scientific study. Tinklepaugh had monkeys watch as either lettuce or banana was placed under one of two cups, the other cup being left empty. The monkeys were taken away for a few minutes and then returned and allowed to choose a cup. They all chose the one with food, though with much greater enthusiasm when they had seen the banana placed under the cup.

Suppose the monkey sees lettuce placed under the left-hand cup before being taken out of the room. Most non-behaviorists would say that the monkey has learned that there is lettuce under the left-hand cup. Behaviorists, though, denied that the monkey had a mental state of “knowing that there was lettuce under the left-hand cup.” Their claim was that the lettuce merely served to reinforce the link between the stimulus (the sight of the cup) and the response (looking under the cup). They denied that the monkey had learned anything about the lettuce at all. To test between the behaviorist and the “common sense” interpretations, Tinklepaugh did another experiment. This time he let the monkey see banana being placed under the cup, but when the monkey was out of the room, he replaced the banana with lettuce. When the monkey was returned to the room, here is what happened:

“Subject rushes to the proper cup and picks it up. Extends hand towards lettuce. Stops. Looks around on floor. Looks in, under, and around cup. Glances at other cup. Looks back at screen. Looks under and around self. Looks and shrieks at any observer present. Walks away, leaving lettuce untouched on floor (p. 8).”

I’d say that was one pissed off and disappointed monkey. After citing other more rigorous tests of this nature, Cheney and Seyfarth conclude:

“The results of these experiments challenge the more extreme behaviorists’ view that mental states like knowledge, beliefs, or expectations cannot be studied scientifically and may even be an illusion. Instead, they support Tolman’s view that learning allows an animal to form a mental representation of its environment. Through learning, animals acquire information about objects, events, and the relation between them. Their knowledge has content, and this content can be studied scientifically (p. 9).”

In fact, there are many books that report on scientific studies of consciousness. Adam Zeman’s Consciousness: A User’s Guide is a good one. There is even an Association for the Scientific Study of Consciousness. Check their website. Maybe Mr. Georgoudis means to claim that such studies can only address what David Chalmers calls the “easy problem” about consciousness, viz., how brain processes and conscious states relate, but cannot address the “hard problem,” that is, to explain why there should be phenomenal consciousness at all. This is the famous “explanatory gap” between information about brain states and processes, however complete, and the fact that things feel a certain way. We might explain in complete detail the underlying neurological processes involved in feeling pain, but this does not tell us why it hurts when such processes are occurring. Similarly, Frank Jackson tells the story of one hypothetical “Mary” who has complete scientific knowledge about the physiology of color perception. She can tell you precisely what occurs in your head when you have the experience of seeing a red rose. Yet Mary herself has been raised in a purely black-and-white environment. Then, one day, she has the experience of seeing a red rose. Only then does she discover what it is like to see a red rose; all of her scientific knowledge could not tell her that. Then there is the question Thomas Nagel put to us: What is it like to be a bat? We could have complete knowledge of the bat’s faculty for echolocation, but that would still not tell us what it phenomenally feels like to echolocate like a bat. Don’t all these puzzles show that natural science can never explain science and that we have to look beyond nature for an adequate explanation?

Let’s ponder this question a bit more: Why do so many thoughtful people (many of them metaphysical naturalists) think that neuroscience can never explain consciousness? Because it seems to them that even a completed neuroscience cannot tell us what we really want and need to know. It seems that neuroscience can only succeeded in displaying deep correlations between brain states and states of our phenomenal consciousness without explaining how anything like, e.g., pain, ideas, or blueness could come from anything like brain processes. At some point in a ground-up scientific explanation, consciousness will be seen to emerge within a physical system, and some philosophers will still see a vast, unbridgeable explanatory chasm here. Science, it appears, may someday tell us how states of consciousness occur by giving us an exhaustive list of their physiological correlates, but we cannot expect an account of why conscious states would be expected to arise from those functions of physical systems. In short, even at the end of the day neuroscience seemingly can only give us correlations, not explanations, only hows, not whys.

However, as William Lyons observes (Lyons, Matters of the Mind, p. 204), there is no sharp dividing line between “how” explanations and “why” ones. As he notes, the answer to the query why, given that metal expands when heated, railway lines do not buckle in hot weather, will explain why by detailing how the lines are constructed and laid so as not to buckle as they expand (Lyons, 205). In this case, explaining how is also explaining why, and there seems to be no reason why, in principle, this should not also be the case with the explanation of consciousness:

“It seems likely that if scientists could explain how, neurophysiologically and biochemically, the parts of our brain causally relevant to consciousness are put together and function in relation to one another, then ipso facto the scientists will have explained how those parts function together so as to generate consciousness (Lyons, 206; emphasis in original).”

Why is there consciousness? Because there are brains that are organized and function in these particular ways; this is how they work and that is why there is consciousness. The feeling that in this case, as opposed to the railway tracks case, a how-explanation still leaves us wondering “But why?” may really be no more than that—a feeling. The neuroscientific account, when and if it is completed, may leave us with a sense of mystery, but that may be a feeling that we will eventually get over. On numerous occasions in the history of human inquiry, certain questions have been

dropped, not because they were answered, but because there no longer seemed to be any point in asking them.

But the whole discussion so far has failed to ask two most pertinent questions: (1) Why should MN have the burden of explaining consciousness? (2) Is there any prospect that any ontology inconsistent with MN, say Cartesian dualism, could do a better job of explaining consciousness? Let’s take the second question first. To say that we think because we possess a soul, a “thinking substance” is most emphatically not to explain thought or any other aspect of consciousness. Such an “explanation” is really just like the old joke from Moliere about explaining the sleep-inducing effects of opium by saying that it has a “dormative potency.” You don’t explain the phenomenon; you just pretentiously and tendentiously re-name it. Souls explain consciousness no better than matter does; a lot worse, in fact. By definition, we can have no inkling about how an incorporeal posit like a soul is supposed to operate. Its functioning, in principle, is entirely occult. At least with matter we can, in principle, have “how” explanations of consciousness.

Well, why not just postulate consciousness as a primitive, as the idealists did? That is, consciousness is taken as a, maybe the, basic reality with “matter” only an epiphenomenon of mind. Because one of the most obvious things we know about consciousness is that, so far as we can tell, it occurs only in association with the physiological functioning of very complex organic entities that appear quite late in the evolution of the universe. We know this with as much certainty as we know any scientific fact. We know it as a scientific fact that at one time, probably quite recently in the geological sense, nothing on earth was conscious. Were trilobites conscious? Dinosaurs? Homo erectus? Further, even if consciousness has its own causal powers, and is not merely epiphenomenal, clearly its existence and nature are dependent, wholly and in detail, on quite subtle physical conditions. This takes us back to question (1).

In response to question (1), MN does not have the burden of explaining consciousness; it is quite sufficient to know (which we do) that consciousness is wholly dependent upon the quite precise functioning of certain physical processes. In fact, all of the evidence indicates that particular physiological changes in the central nervous system are sufficient for changes in consciousness. Quite subtle changes in your brain chemistry can turn you (yes, you) into a raving lunatic, sex addict, or gun-totin’ goober who thinks that Barack Obama is not a natural born U.S. citizen. The books of Oliver Sacks are quite instructive on these points. He shows with great eloquence how brain disease and trauma can change consciousness in quite remarkable and sometimes quite terrifying ways. One of his stories tells of a man, an artist, who suffered a head injury and could no longer see colors. He not only could no longer see colors, he could not even form a mental image of colors. He was like Frank Jackson’s “Mary.” Less frightening is Sacks’ story about the 90 year-old woman who began to feel young again, even with a renewal of libido. Turns out that she had contracted syphilis when young, and, after seventy years of dormancy, the spirochetes had become active in her brain. Sacks killed the spirochetes with penicillin and left her with her perky feelings. When anything, from spirochetes to speed, changes your brain functioning, it changes YOU.

Paul Churchland has a fascinating section in The Engine of Reason, the Seat of the Soul about the physiology of taste perception. The qualitative difference between two very different tastes, say limburger cheese and ripe peach, comes down to different levels of stimulation of a quite small number of different kinds of taste receptors on the tongue. Somewhat simplifying, if there are ten different levels of excitation for each of four different kinds of receptors—sweet, sour, bitter, and salty—then there will be 104 or 10,000 different states of excitation, which we can represent by ordered quadruples from (1,1,1,1) to (10,10,10,10). These will correspond to 10,000 distinct and discernable qualitative differences in “taste space.” Thus the taste of limburger cheese would be something like a (2,2,6,7) state of stimulation for the sweet, sour, bitter, and salty receptors respectively, and ripe peach would be (8,6,2,1) or something like that. Now, we might still insist that such correlations tell us nothing about why those particular tastes, or any taste at all, would always be associated with those, and only those, levels of cellular stimulation. But they are. This is just as MN would expect, and that is the crucial point. By the way, Cartesian dualism has no way of explaining why the features of consciousness should be correlated in such a comprehensive and fine-grained way with the detailed operations of wetware. As far as Cartesian dualism or idealism can say, we should be capable of having the same sort of consciousness we presently enjoy if our skulls were full of lime Jell-o. I cannot think of anything the dualist or the idealist could say here that would not be dreadfully ad hoc (or, less politely, ass-covering).

The upshot is that I do not see that the phenomenon of consciousness presents any special problem for MN. There may be aspects of consciousness that will always be a mystery, or at least will feel mysterious for us, but I do not see how any alternative to MN helps in that regard. I’ll end with a challenge: Show me any instance in which two identical states of an organism’s central nervous system are correlated with two distinctly different states of consciousness, and I’ll have to admit that the phenomena of consciousness constitute a legitimate challenge to my worldview.