What It Is Like to Be a Bat
There is a confusion in the philosophy of mind concerning the possibility of offering a scientific explanation of the nature of consciousness. As this confusion seems best embodied in Thomas Nagel's famous essay, “What Is It Like to Be a Bat?” these remarks are framed as a direct response to that question.
The confusion resides in the distinction between subjective and objective facts. An objective fact is one that can be completely described by language. A subjective fact is one that has an experiential aspect to it. Of course, it can be described by language (since language can be deployed to describe anything); however, it cannot be completely described by language because there is “something that it is like” within this fact, and therefore a complete representation requires the experience as well. (There are, no doubt, tricky philosophy-of-language issues that are raised by the above, but this simple definition will serve us for this discussion.)
Qualia are subjective facts. (Whether all subjective facts are qualia need not concern us here; the key point is that all qualia are subjective facts.) Hence, qualia cannot be completely described by language. It is easy to grasp this intuitively when we think about our everyday experience. For example, when someone describes some subjective experience, we understand that in order to grasp more fully what is being described, one must imagine oneself in that person’s experience. The description facilitates the effort, but the effort is necessary nonetheless. That we are (sometimes) successful in making this active effort is explained by the essential similarity we all share as human beings.
Now comes the confusion. It has become respectable to argue that the subjective nature of qualia suggests that a purely physicalist account of consciousness may not (or should not, or cannot) be possible. I believe this is clearly wrong. It is true that we do not at present have a physicalist account of consciousness, and may also be true that such an account is far off. (We will almost surely not have one in my lifetime, for example.) It is even possible that there will turn out to be some reason why a physicalist account may not (or should not, or cannot) be possible. But we have no reason at present to believe that a physicalist account would not be possible. Instead, we have every reason to believe that such an account should be possible, at least in principle, because we are all physical beings in the world and consciousness is a physical phenomenon.
To further clear up this confusion, let’s describe how we would determine what it is like to be a bat.
It is surely undeniable that bats have qualia. But bats, unlike people, cannot describe their qualia. And furthermore, we are enough dissimilar to a bat (e.g. we have no sense that is analogous to a bat’s sonar) that even if somehow we were presented with a description of a bat’s qualia, it seems unlikely that we could imagine ourselves into a bat’s experience. A more fundamental approach is necessary.
Before describing this fundamental approach, it may be useful to elaborate upon the normal process of imagining what another person’s qualia are like. Let’s take a simple example, like someone explaining what a meal you did not have tasted like. She might describe the tastes and compare it to other foods that you have recently eaten. You might close your eyes to eliminate competing physical sensations and then direct yourself to imagine the food. Somehow, your conscious effort might allow you to reconstruct and imagine (albeit faintly and inadequately) the relevant gastronomic qualia. At the time of this writing, we do not have anything like a complete physical description for how this process happens. But does anyone seriously doubt that it is at root a physical process? The sounds of the words hit the eardrum and are converted into signals that are processed (somehow) by the brain; the conscious faculty decides (somehow) to imagine the physical sensations conveyed by the signals; the brain (somehow) simulates the physical sensations and (somehow) conjoins those sensations to its understanding of the words, etc. Even though we cannot now provide any sort of adequate physical description of the entire process, do we have any reason to doubt that it is entirely a physical process? And furthermore, do we have any reason to believe that such a description is inherently impossible? I believe the answer to both of these questions is no.
If I am right that the last two questions are correctly answered in the negative, then it follows that we could in principle replicate scientifically what normal, human empathy approximates interpersonally all the time. Furthermore, this replication could be applied far beyond the limits of human empathy, both in terms of scope (applying to bats as well as humans) and representativeness (going far beyond what our normal imagination is capable of). Of course, there might be some scientific reason why such laboratory replication turns out to be inherently impossible. You never know what you will learn until you try: nobody living before the twentieth century would have been likely to guess the inherent physical limitations of the speed of light and the uncertainty principle, for example. Perhaps some physical limitation applies to the replication of consciousness.
But the possibility of a physical limitation of our ability to replicate qualia is completely different from the philosophical claim that “every subjective phenomenon is essentially connected with a single point of view, and it seems inevitable that an objective, physical theory will abandon that point of view.” [Nagel, http://organizations.utep.edu/portals/1475/nagel_bat.pdf, page 2] I contend that this seeming inevitability stems simply from a lack of philosophical imagination.
So now let’s describe the fundamental approach that would result in a physical theory that would meet our needs.
The first step is to develop a sufficient understanding of a bat’s brain (and associated neurological system) to create whatever qualia are desired. Let us suppose that we want to know what it is like for a bat to perceive the wall of a cave using sonar. Then we must understand the bat’s brain in sufficient detail to know precisely what physical processes are associated with “perceiving this wall under these circumstances using sonar”. In doing so, we must learn precisely where the conscious states that are associated with such perception are located, and we must identify every single relevant feature of the brain that is associated with such conscious states.
Of course, we are nowhere close to being able to do anything of the sort. It would require a body of knowledge and an empirically verified theory of bat brain physiology that is completely beyond us today. But I do not know any reason why this would be inherently impossible; it just means that our science is many, many years away from such understanding. And anyway, this is the easy part! For once we have a complete physical description of bat qualia in question, verified (however it would be verified) by experiment and theory, we must move to the second step. The qualia must be replicated in a human brain in such a way that it can be experienced by a person.
The hypothesis here is that bat brain physiology and human brain physiology are sufficiently similar that specific bat qualia can be recreated in a human brain. Of course, this may not be true: but again, we have no reason to assert with any philosophical justification that it cannot be done. The key would be to identify whatever bat stimuli are associated with specific conscious states and then reproduce those stimuli under conditions that are both theoretically justified and empirically verifiable. Under such conditions, we would have at least some reason to believe that whatever qualia would then be perceived by our human subject would represent how the qualia are perceived by the bat. Our human subject would know what it is like to be a bat.
"But wait a minute!" one might imagine our philosopher objecting. "How would we know that the qualia as experienced by the human subject would be the same as that experienced by the bat? Science is wrong all the time (indeed, that is the very point of the scientific method) so no one can know for sure that the recreated qualia in the human subject are the same as in the bat. Only the bat has unmediated access to its own qualia." Well, sure. But the special epistemological status of one's own mental states has been known since Descartes, yet the general response is not to slide into solipsism. Furthermore, we don't have to relitigate whether it is possible to have synthetic a priori knowledge to make a convincing scientific case. If we have sufficient empirical knowledge and a sufficiently justified theory to explain and predict bat qualia and the recreation of such qualia in a human subject, then we would have sufficient evidence that the qualia as experienced by the human subject would be the same as the qualia as experienced by the bat.
The question at hand was whether it is possible to provide a justified physicalist account of conscious mental states. Our answer is as follows. “In practice: not today. In theory: we have every reason to believe so and no obvious reason to think not, although we won’t know for sure until we try. Of course, since subjective facts cannot be fully described objectively, our objective, physical theory will require a subject to experience the qualia, and only that subject will have the experience. But that is just the nature of subjective facts.”
What is it like to be a bat? We don’t know today, but we have every reason to believe that it is in theory knowable. More importantly, until we learn far more than we know today we are wasting our time raising philosophical objections to the possibility of such knowledge.