Why Is There Nothing It’s Like to be a Rock?
We divide the world into two big classes: the conscious beings and the non-conscious beings. The mind-body problem concerns the conscious beings: we want to know what makes it the case that a being is conscious. This is an explanatory question: we seek an explanation for the presence of consciousness in certain beings—we want to know why those beings are conscious. More specifically, we want to know what properties of the brain explain the presence of consciousness. How does consciousness emerge from the brain? What features of the brain give rise to consciousness? And the problem is that we find it difficult to discover any features that explain the emergence of consciousness in those cases in which it emerges. The conscious beings seem similar to the non-conscious beings in all fundamental respects except consciousness, so we can’t see why we have consciousness in some cases but not in others. We need to identify something common and peculiar to all the conscious cases, but at the physical level we find homogeneity between conscious beings and non-conscious beings—it is all molecules in motion, roughly. By rights, we feel, the conscious beings shouldn’t even be conscious, given their similarity to the non-conscious beings: but they are—puzzlingly, inexplicably. Thus we declare the existence of consciousness in a physical world a mystery, more or less deep. We don’t know what accounts for the presence of consciousness in the world.
I have no wish to rehash this familiar story here; my mission, rather, is to note that there is an exactly parallel problem concerning the absence of consciousness in non-conscious beings. Hence my title: why is a rock notconscious? This is also a mind-body problem—the problem of explaining the lack of mind in certain things. And the problem is the same as before: these non-conscious things are too similar to conscious things for it to be intelligible that one class of things has consciousness while the other does not. We don’t know why there is no emergence of consciousness in the things we take not to be conscious—which raises the possibility that these things might be conscious after all. What properties do rocks lack that makes us so sure they are not conscious? If consciousness can arise from physical brains, seemingly miraculously, why can’t it arise from other physical configurations in the same way? In any case, we have a problem explaining why consciousness is distributed as we suppose it to be, since we don’t know what explains its presence or absence.
In other cases we can explain absence quite easily. If we want to explain the absence of liquidity in ice, we appeal to the fact that frozen water does not permit the constituent H2O molecules to slide over each other. If we want to explain why snow isn’t hot, we observe that it has low molecular motion. If we want to explain why rocks don’t photosynthesize, we point out that they don’t contain photoreceptors and chlorophyll. If we want to explain why fleas are not good at arithmetic, we note the absence of a complex brain. Since we know what makes a thing have these various attributes, we also know what makes a thing lack them. But we don’t know what explains the presence of consciousness, so we can’t cite the absence of that to explain the absence of consciousness. If electrical activity in the brain were the basis of consciousness, then we could simply cite its absence to explain why non-conscious things are non-conscious–but that is precisely what we don’t know. And if we tried to use that test, we would end up spreading consciousness far more widely than we tend to, electricity being virtually everywhere.
The problem already arises within the organic world. Some organisms are conscious, but it is not generally supposed that all are—some insects and worms are not, nor are bacteria and viruses, nor are plants. Yet all are living things, some of them even containing neurons. How do we explain the lack of consciousness in these organisms, given its presence in other organisms? And if we can’t, isn’t it dogmatic to restrict the attribution of consciousness in the way we do? Aren’t we being entirely arbitrary in our ascriptions of consciousness, possibly even anthropocentric? We have an absence-of-mind problem in these cases: we can’t say what it is about the body of the organism that precludes it from being conscious—just as we can’t say what it is about the body of other organisms that guarantees that they are conscious Thus the mind-body problem takes two forms: explaining presence and explaining absence. Each form generates a potential skeptical problem: on the one hand, suggesting that consciousness might be an illusion, since it cannot be explained in terms of the body; on the other hand, suggesting that consciousness might be everywhere, since we can’t find a way to confine it as we customarily do. How do we rule out eliminativism and how do we rule out panpsychism? It isn’t that these extravagant doctrines are entailed by the two sides of the mind-body problem, nor even that they have any intrinsic plausibility, but they do arise naturally once the full explanatory problem is confronted. In particular, it isn’t easy to rebut the claim that consciousness might be more widespread than we tend to suppose—as with the popular possibility of consciousness in trees. For what is it that trees lack that excludes them from the class of conscious beings? They are multi-cellular, DNA-based organisms that adapt to their environment—why should the presence of a clump of squishy grey matter be regarded as the decisive criterion? We are accordingly admonished to keep an open mind.
Putting arboreal sentience aside, we should acknowledge that the mind-body problem applies more widely than traditionally recognized—not just to things with minds but also to things without minds. The problem is an explanatory one, and it applies as much to the absence of consciousness as to its presence. What explains the absence of consciousness in the brain stem or in peripheral nerves but its presence in the cerebral cortex or other central nerve tissue? Why are bats conscious but not gnats (or slugs or jellyfish)? Why is there nothing it is like to be a rock? The null phenomenology needs to be explained as much as the brimming phenomenology. No matter how much we learn of a gnat’s brain or a rock’s mineral structure we will not see why these things lack consciousness. At the end of our inspection we will only be able to say, “It might be conscious for all we know”. We can’t say this after examining the internal structure of ice and wondering about its liquidity: it can’t be liquid given the molecular situation. By contrast, the lack of consciousness in some things is puzzling in view of the similarities between conscious things and non-conscious things. It is not that the presence of consciousness is deeply mysterious while its absence is not; both are mysterious.  It is a mystery why rocks are not conscious (they contain molecules, just like conscious brains). We can explain why rocks can’t sing or walk or bend, but we can’t explain why they don’t have their own form of rock consciousness—just as we can’t explain why we do have our own form of human consciousness.
The dualist claims that nothing about the body can explain the mind, so we need to recognize a separate reality to accommodate the mind. We should not expect to find anything in the brain that could add up to the mind. Applying this way of thinking to the rest of nature, we get the result that the inadequacy of bodies in general (including rocks) to ground consciousness is no reason to deny that they are conscious—all bodies might have an associated mind that exists in its own right and without benefit of bodily foundation. How can such a doctrine be refuted? Not by pointing out that brains are inherently capable of producing consciousness by virtue of possessing a special property P, while rocks conspicuously lack P—since we know of no such property. If we insist on absence in the one case but not in the other, we incur the charge of mental chauvinism. We can’t explain absence, according to dualism, by pointing to the lack of intrinsic grounding properties in the rock, just as we can’t explain presence by pointing to suitable grounding properties in the brain. Absence is as puzzling as presence. Thus we have a not-mind/body problem—the problem of explaining why some things don’t have minds. Even zombies have a mind-body problem—the problem of why they are zombies. I think myself that we can be confident that the way we distribute minds across nature is more or less correct (extending consciousness as far as many insects), so I am convinced that there is a deep difference between things that are conscious and things that are not.  But I accept that I have no idea why consciousness is present in some cases and absent in others. To me it is a mystery why rocks are not conscious, though I am morally certain they are not. I just don’t know why there is nothing it’s like to be a rock.
 I take these to be forms of extreme skepticism, analogous to other kinds of philosophical skepticism; I don’t think they are serious real possibilities. But they do point to areas of ignorance and opacity.
 If for some reason we had decided (wrongly) that the brain is not the organ of consciousness, we would find nothing to challenge our opinion in the known properties of the brain. We would regard the brain as we now regard a rock—as somehow obviously not a seat of consciousness. The mystery is why some things are conscious and some things are not, given that they seem not to differ all that dramatically (the substance is the same).
 That is, I believe we have adequate evidence for ascribing consciousness as we do (though all evidence is fallible), but I don’t believe we have any explanation for the presence of consciousness in some beings and the absence of consciousness in others. Thus the lack of consciousness is a mystery just as the presence of consciousness is a mystery; indeed, they are aspects of the same mystery.