“… imagine that one has webbing on one’s arms, which enables one to fly around at dusk and dawn catching insects in one’s mouth; that one has very poor vision, and perceives the surrounding world by a system of reflected high-frequency sound signals; and that one spends the day hanging upside down by one’s feet in an attic. In so far as I can imagine this (which is not very far), it tells me only what it would be like for me to behave as a bat behaves. But that is not the question. I want to know what it is like for a bat to be a bat.”
In the philosophy of mind the US philosopher Thomas Nagel’s 1974 article “What is it like to be a bat?” has probably been more influential than any other paper published in recent times. Nagel succinctly captures the essence of the discontent that many feel with current attempts to analyze our mental life and consciousness in purely physical terms. As such his paper has almost become a totem for philosophers dissatisfied with such physicalist and reductive theories of mind.
“Without consciousness the mind-body problem would be much less interesting. With consciousness it seems hopeless.”
Thomas Nagel, 1979
The bat perspective Nagel’s central point is that there is a “subjective character of experience”—something that it is to be a particular organism, something it is like for the organism—that is never captured in these reductive accounts. Take the case of a bat. Bats navigate and locate insects in complete darkness by a system of sonar, or echolocation, by emitting high-frequency squeaks and detecting their reflections as they bounce back from surrounding objects. This form of perception is completely unlike any sense that we possess, so it is reasonable to suppose that it is subjectively completely unlike anything we are able to experience. In effect, there are experiences that we as humans could never experience, even in principle; there are facts about experience whose exact nature is quite beyond our comprehension. The essential incomprehensibility of these facts is due to their subjective nature—to the fact that they essentially embody a particular point of view.
There is a tendency among physicalist philosophers to cite examples of successful scientific reduction, such as the analysis of water as H2O or of lightning as an electrical discharge, and then to suggest that these cases are similar to the analysis of mental phenomena in terms of physical phenomena. Nagel denies this: the success of this kind of scientific analysis is based on moving toward greater objectivity by moving away from a subjective point of view; and it is precisely the omission of this subjective element from physicalist theories of the mind that makes them incomplete and unsatisfactory. As he concludes, “it is a mystery how the true character of experiences could be revealed in the physical operation of that organism,” which is all that science has to offer.
What Mary didn’t know Nagel is apparently content to leave the matter as a mystery—to highlight the failure of recent physicalist theories to capture the subjective element that seems to be essential to consciousness. He professes to be opposed to these reductive approaches, not to physicalism as such. The Australian philosopher Frank Jackson attempts to go further. In a much-discussed 1982 paper “What Mary didn’t know,” he presents a thought experiment about a girl who knows every conceivable physical fact about color. Now, if physicalism were true, Jackson argues, Mary would know all there is to know. But it turns out that there are things (facts) she doesn’t know after all: she doesn’t know what it is like to see colors; she learns what it is like to see red (etc.). Jackson concludes that there are facts that are not, and cannot be, captured by physical theory—nonphysical facts—and hence that physicalism is false.
From the moment of her birth Mary was confined in a black-and-white room, where she was never exposed to anything that was not black, white or shades of gray. Her education may have been unusual but was certainly not neglected, and by reading books (no color books of course) and watching lectures on black-and-white television, she eventually became the world’s greatest scientist. She learned literally everything there was to know (and could ever be known) about the physical nature of the world, about us and about our environment. Finally the day came when Mary was let out of her monochrome room and into the world outside. And what a shock she had! She saw colors for the first time. She learned what it was like to see red and blue and yellow. So, even though she knew every physical fact about color, there were still things about color that she didn’t know …
Moral: (1) there are some facts that are not physical; (2) be very careful how you pick your parents.
Committed physicalists are not, of course, persuaded by Jackson’s argument. Objections are leveled primarily at the status of his so-called “nonphysical facts”: some critics accept that they are facts but deny that they are nonphysical, others assert that they are not facts at all. The root of these objections is generally that Jackson has begged the question against physicalism: if physicalism is true and Mary knows all the physical facts that could ever be known about color, then she will indeed know all there is to know about redness, including subjective experiences associated with it. There is also a suspicion of the masked man fallacy in the way Jackson uses Mary’s psychological states to make the necessary distinction between physical and nonphysical facts.
Whatever the strength of the arguments against Mary, it is hard not to feel that both Jackson and Nagel have put their finger on something—that something essential is missing from the versions of physicalism that have been proposed to date. It is perhaps safe to conclude that the issue of accommodating consciousness in a purely physical account of the world still has plenty of life left in it.
According to Leibniz’s law or the “identity of indiscernibles,” if two things, A and B, are identical, every property of A will be a property of B; and hence, if A has a property that B lacks, A and B are not identical. Now Bertie thinks that Bono is the greatest rock star in the world, but he has no view about Paul Hewson (he doesn’t realize that it is in fact Bono’s original name). That means that Bono has a property that Paul Hewson lacks—the property of being thought by Bertie to be the greatest rock star in the world—so, according to Leibniz’s law, Bono is not the same person as Paul Hewson. But he is, so something has gone wrong with the argument. The problem is due to the so-called masked man fallacy: I don’t know who the masked man is; I know who my brother is; therefore my brother is not the masked man. The root of the fallacy is that subjective views or beliefs about something are not real properties of that thing: you can know something under different descriptions, just as different people can have different beliefs about the same thing.
Now, does Frank Jackson’s thought experiment about Mary commit the masked man fallacy? Physicalist opponents have argued that he uses the “wrong kind” of property to establish a duality of physical and nonphysical facts. But in reality, they argue, there is only one kind of fact (physical facts) that can be given different, essentially subjective descriptions: two ways of looking at the same thing.
the condensed idea
Inside a bat’s mind?
| Timeline | |
|---|---|
| c.250BC | Do animals feel pain? |
| AD1637 | The mind-body problem |
| 1655 | The ship of Theseus |
| 1912 | Other minds |
| 1953 | The beetle in the box |
| 1974 | What is it like to be a bat? |