Do You Only Have a Brain? On Thomas Nagel
There is a response to this kind of challenge, one that is widely embraced by philosophical naturalists (though, again, not mentioned by Nagel). This response starts by noting that we determine what is “rational” or “justified” simply by appealing to the most successful forms of inquiry into the world that human beings have developed. Paradigmatic examples of those successful forms of inquiry are, of course, physics, chemistry and biology. They are successful precisely in the way that Aristotelian science was not: they enable us to navigate the world around us, to predict its happenings and control some of them. To confuse one’s intuitive confidence in the logical and epistemic norms that make these sciences possible with some kind of a priori access to the “rational order of the world,” as Nagel puts it, is to forget whence that confidence derives—namely, the very success of these sciences. For philosophical naturalists, the charge of circularity is empty, akin to suggesting that the need for a usable table to have legs requires some justification beyond the fact that the legs actually do a necessary job.
Philosophical naturalists often appeal to the metaphor of “Neurath’s Boat,” named after the philosopher who developed it. Our situation as inquirers trying to understand the world around us, according to Neurath, is like that of sailors who must rebuild their ship while at sea. These sailors do not have the option of abandoning the ship and rebuilding a new one from scratch. They must, instead, try to rebuild it piecemeal, all the time staying afloat on other parts of the ship on which they continue to depend. In epistemological terms, we are also “at sea”: we cannot abandon all the knowledge about the world we have acquired from the sciences and then ask what we really know or what is really rational. The sciences that have worked so well for us are precisely our benchmark for what we know and what is rational; they’re the things that are keeping us “afloat.” Extending this metaphor, we can say that Nagel is the sailor who says, “I know the ideal form a ship should take—it is intuitively obvious, I am confident in it—so let us jump into the ocean and start building it from scratch.”
We agree with Nagel that if the sciences could not explain our capacity to have thoughts about the world around us, that would be a serious failing and a reason to call their findings into question. But they can and they do! It is here that Nagel’s lack of engagement with contemporary cognitive science and his idiosyncratic views about what a scientific explanation should look like make his argument especially perplexing. He writes, in what might seem a massive concession to his naturalistic opponents, “The appearance of animal consciousness is evidently the result of biological evolution, but this well-supported empirical fact is not yet an explanation—it does not provide understanding, or enable us to see why the result was to be expected or how it came about.” On Nagel’s view, consciousness arose from evolution, but despite knowing this fact, we have not explained the origin of consciousness. In a similar vein, Nagel writes:
It is not an explanation to say just that the physical process of evolution has resulted in creatures with eyes, ears, central nervous systems, and so forth, and that it is simply a brute fact of nature that such creatures are conscious in the familiar ways. Merely to identify a cause is not to provide a significant explanation, without some understanding of why the cause produces the effect.
Nagel endorses the idea that explanation and prediction are symmetrical: “An explanation must show why it was likely that an event of that type occurred.” In other words, to explain something is to be in a position to have predicted it if we could go back in time. He also writes, “To explain consciousness, a physical evolutionary history would have to show why it was likely that organisms of the kind that have consciousness would arise.” Indeed, he goes further, claiming that “the propensity for the development of organisms with a subjective point of view must have been there from the beginning.”
This idea, however, is inconsistent with the most plausible views about prediction and explanation, in both philosophy and science. Philosophers of science have long argued that explanation and prediction cannot be fully symmetrical, given the importance of probabilities in explaining natural phenomena. Moreover, we are often in a position to understand the causes of an event, but without knowing enough detail to have predicted it. For example, approximately 1 percent of children born to women over 40 have Down syndrome. This fact is a perfectly adequate explanation of why a particular child has Down syndrome, but it does not mean we could have predicted that this particular child would develop it. Causes alone are frequently deemed sufficient to explain events; knowing enough to predict those events in advance is an important scientific achievement, but not essential to explanation.
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Nagel doesn’t think so, and because of that, he advocates the reintroduction of teleological reasoning into science. (Teleology—the idea that natural phenomena have built-in purposes or ends—was central to Aristotelian science, and it remained very influential until the scientific revolution.) In his discussion of the origin of life, Nagel says that natural teleology would mean that, “in addition to physical law of the familiar kind, there are other laws of nature that are ‘biased toward the marvelous.’”
This is an astonishing though certainly evocative phrase (Nagel adapts it from another writer), yet Nagel offers no further explication of it. He does admit that this proposal “flies in the teeth of the authoritative form of explanation that has defined science since the revolution of the seventeenth century.” Unfortunately, he is also extremely unclear about what he means by “natural teleology,” other than assuring the reader that it is neither part of standard physical laws nor the introduction of theology. One might think that “principles of self-organization or of the development of complexity over time,” which Nagel gives as examples of natural teleology, are the sort of things studied by mainstream protein chemists, developmental biologists and condensed-matter physicists. But apparently these sciences, which study how complex order can be built up from simple physical processes, are not on the right track. Nagel never explains why.
We conclude with a comment about truth in advertising. Nagel’s arguments against reductionism are quixotic, and his arguments against naturalism are unconvincing. He aspires to develop “rival alternative conceptions” to what he calls the materialist neo-Darwinian worldview, yet he never clearly articulates this rival conception, nor does he give us any reason to think that “the present right-thinking consensus will come to seem laughable in a generation or two.” Mind and Cosmos is certainly an apt title for Nagel’s philosophical meditations, but his subtitle—”Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False”—is highly misleading. Nagel, by his own admission, relies only on popular science writing and brings to bear idiosyncratic and often outdated views about a whole host of issues, from the objectivity of moral truth to the nature of explanation. No one could possibly think he has shown that a massively successful scientific research program like the one inspired by Darwin’s theory of evolution by natural selection “is almost certainly false.” The subtitle seems intended to market the book to evolution deniers, intelligent-design acolytes, religious fanatics and others who are not really interested in the substantive scientific and philosophical issues. Even a philosopher sympathetic to Nagel’s worries about the naturalistic worldview would not claim this volume comes close to living up to that subtitle. Its only effect will be to make the book an instrument of mischief.
Why has natural selection always been the most contested part of evolutionary theory? asks Jeffrey A. Coyne in “The Improbability Pump” (May 10, 2010), reviewing The Greatest Show on Earth, by Richard Dawkins, and Jerry Fodor and Massimo Piattelli-Palmarini’s What Darwin Got Wrong.