Nagel’s bat doesn’t demonstrate incompleteness in materialist science

Philosopher Thomas Nagel is well known for rejecting the idea that science can explain all aspects of the human condition, a view expounded in his influential paper “What is it like to be a bat?”, and recently in a book trying to overturn materialist Darwinism as an inadequate explanation of life (Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False). Nagel sums up his argument in the New York Times:

… it seems natural to think that the physical sciences can in principle provide the basis for an explanation of the mental aspects of reality as well …

However, I believe this possibility is ruled out … The physical sciences can describe organisms like ourselves … but they cannot describe the subjective experiences of such organisms or how the world appears to their different particular points of view. There can be a purely physical description of the neurophysiological processes that give rise to an experience, and also of the physical behavior that is typically associated with it, but such a description, however complete, will leave out the subjective essence of the experience — how it is from the point of view of its subject — without which it would not be a conscious experience at all.

So the physical sciences, in spite of their extraordinary success in their own domain, necessarily leave an important aspect of nature unexplained.

Let’s clarify what the materialist account of a “subjective experience” is. The brain is a network of neurons, connected to each other by dendrites and synapses. Electrical and chemical signals flow through the network in complex patterns. Those patterns are our thoughts. Our thinking and deliberation and decision-making are patterns of electrical firing flitting around our neural-network brain. A particular thought, a particular sensation, or a particular subjective experience, are all particular patterns of electrical firing.

Nagel is asserting that we can understand every physical aspect of this phenomenon, having a complete knowledge of the network and the electrical signals, and yet not understand “the subjective essence of the experience”, and thus not understand what it is like to be a bat. From there he rejects materialism as incomplete, and goes on to reject any materialist account of life.

My reply is, yes, Nagel is right, indeed we cannot always appreciate the subjective essence of an experience, but that is not a limitation of materialism and not a limitation of materialist science.

First, let’s consider when we can and do appreciate the subjective experience of someone else. If we can empathise with someone who is sad, it is because we have been sad. What we subjectively appreciate is our experience of being sad, which we assume to be sufficiently similar to the experience of the person feeling sad. But suppose we had never had a headache, could we really appreciate what that felt like, based on a spoken account from someone else? I suggest that we could not, since a headache is sufficiently different from other sensations.

We can never subjectively experience someone else’s subjective experience. All we can do is relate their experience to the closest one of our own. If, in the materialist account, the subjective experience is a particular neural-network firing pattern, then, if two different neural networks (two brains) are sufficiently similar, and if they are in a sufficiently similar firing pattern (a similar state or mood), then they would subjectively experience the same thing. They would subjectively know what it is like to be each other.

For us to be able to subjectively experience being a bat we would — in the materialist account — have to have a brain neural-network similar enough to that of a bat to have exactly the same firing pattern in our brains as the bat. That is the only way we could appreciate the subjective experience, because “the subjective experience” is that firing pattern.

Clearly, the differences in the neural networks between bats and humans then mean that our subjective experiences can never be sufficiently close, and we can never fully appreciate what it is like to be a bat. Nagel is right on that.

However, I fail to see why this is a failure or incompleteness of materialism or of materialistic science. Indeed, the materialist account explains exactly why we can never subjectively experience what a bat subjectively experiences. This is not a failure of materialism, this outcome is a prediction of materialism!

Under materialism it could not be otherwise. Could I ever be in the state of “running as fast as a cheetah”? No, I could not, biological differences prevent it. Could I ever be in a state of lifting a tree-trunk with my nose, like an elephant? No. (Do either of these statements point to a limitation of materialistic science? No, I don’t see how they do.) Can I ever be in the same brain-state as a different person or animal? Well, no, I can’t (I may get close at times, but overall I can’t). So what?

A critic might reply, but we’re not asking whether humans can appreciate the subjective experience of another animal, we’re asking whether “science” can, whether we can write down a scientific account that does.

I would respond thus: the question, as posed, doesn’t make sense. Are you asking “science” to have a “subjective experience”? OK, well, in principle, science could build a full physical emulation of the bat’s brain and firing patterns, and then say, there, that’s your subjective experience. Of course a human could not access that experience, but then that’s a limitation of the human, not of the scientific knowledge. The limitation is that the human cannot sufficiently alter her brain to fully emulate the firing pattern (if she did she would no longer be human). But science can interrogate the full physical emulation of the bat’s brain and answer any well-posed question about it.

I don’t see any question that science cannot answer. If you ask, “what is the subjective experience like?”, you can point to the emulation and say “that’s what it is like”. But, again, the only way that the human could fully appreciate that subjective experience is to replicate it in their own brain (just as the only way we can know what sadness or headaches are like is through our own experiences). Again, the failure of appreciation results from the limitation of humans. But there is nothing missing from the materialist account.

We should also be clear that limitations of human capability or in our ability to answer questions do not necessarily imply flaws or incompleteness in science. There are many questions that science can never answer: we can never know the names of every solider who fought in all of Alexander the Great’s battles, because the information no longer exists in the universe. This is not an incompleteness of science, unless some other method can answer the question.

So could some new science, which surpasses the old “materialist science”, lead to humans actually appreciating the subjective experience of a bat? This is Nagel’s fond dream, which he hankers after at book length in Mind and Cosmos, despite giving not even an outline of how it might work. Again, the very idea makes little sense, the idea that one could warp a human’s brain into the same firing pattern as that of a bat (which is the only way that a human could subjectively experience being a bat) is as nonsensical as the idea that one could warp a human body to run as fast as a cheetah.

The only resort from there would be to adopt full-blown dualism, to appeal to “mind” as something totally other than matter. This might appeal to humans intuitively, but has got nowhere as a serious research program. For example, Sean Carroll outlines why it would mean over-turning most of physics, the most successful research program humans have ever had. And we’re hardly going to do that without very good reason and evidence, which Nagel simply has not provided. The intuitive idea that our inability to empathise with a bat shows a limitation of materialist science comes, I submit, simply from a failure to think through what subjectively experiencing what a bat experiences would actually entail.

Note: For other responses to Nagel’s argument read H. Allen Orr, Jerry Coyne, Sean Carroll, and Robert Paul Wolff.