From the Dennett-Putnam point of view (though not from that of the many philosophers who insist that mentality is a matter of consciousness, not just of beliefs and desires), there is simply no problem about the relation between the mind and the brain. The brain is the mind under a certain description, and conversely. Nor, seen in this light, is there any problem about whether computers "really" think or dogs "really" infer. Nor is there any problem about what human beings really are. Human beings, like computers, dogs, and works of art, can be described in lots of different ways, depending on what you want to do with them--take them apart for repairs, re-educate them, play with them, admire them, and so on for a long list of alternative purposes. None of these descriptions is closer to what human beings really are than any of the others. Descriptions are tools invented for particular purposes, not attempts to describe things as they are in themselves, apart from any such purposes. Our various slowly evolved descriptive and explanatory vocabularies are like the beaver's slowly evolved teeth and tail: they are admirable devices for improving the position of our species. But the vocabularies of physics and of politics no more need to be integrated with one another than the beaver's tail needs to be integrated with its teeth.

    For philosophers who adopt this pragmatic, biologistic way of thinking about the relation of language to reality, there is no more of a problem about the unity of knowledge than about the unity of the human being. There is no more need to bridge gaps among the natural sciences, the social sciences, the humanities, and the arts than to bridge gaps among atom-by-atom, molecule-by-molecule, cell-by-cell, organ-by-organ, thought-by-thought, character-trait-by-character-trait, and developmental-stage-by-developmental-stage descriptions of an individual person. Each of the various academic disciplines does its respective job, just as each of these descriptions of the individual does its.

   Statements using one sort of description usually cannot be paired off with statements using another descriptive vocabulary. That is what we mean when we say that vocabularies are irreducible to one another. There is no way to find a sentence in molecule--talk that is true just in case the statement "This cell is unusually large" is true. Nor can one find a sentence in neuron-talk that is true just in case "This person is unusual in her preference for Ravel over Brahms" is true. But such irreducibility does not pose philosophical problems. Nor does it fragment knowledge. As we pragmatists see it, there can and should be thousands of ways of describing things and people--as many as there are things we want to do with things and people--but this plurality is unproblematic.

"The unity of science" was a battle cry of the logical positivists in the 1930s and '40s. These philosophers were impressed by the fact that science had explained a good deal about how the atoms come together to make up molecules, molecules to make cells, cells to make organs, and so on. Like Wilson, they wanted to keep this process going until the relations of psychology and political science to biology became as perspicuous as those of chemistry to physics. They thought that science was coextensive with empirical knowledge, and that those parts of the academy that were not scientific--did not offer well-confirmed empirical generalizations--should hang their heads in shame. They believed that the philosophers who disagreed with them should be especially ashamed, for these philosophers were, they claimed, producing "cognitively meaningless utterances." The positivists managed to make lot of people feel guilty: mostly social scientists, but also a few philosophers and literary critics. This guilt caused these people to waste a lot of time trying to make their disciplines scientific.

    During the ensuing 50 years, however, these feelings of guilt have gradually worn off. This slow relief was due in part to the work of Thomas Kuhn and other philosophers of science who had become dubious about the idea of a single "method" or "logic" that tied the "hard" sciences together and which ought to be used in the "soft" ones as well. Those philosophers helped us see that our sense of gratitude to "soft" books (books by, for example, Thorstein Veblen, Max Weber, Nietzsche, Freud, William James, Virginia Woolf, Ruth Benedict, and T. S. Eliot) should remain unaffected by their "unscientific" character--their lack of well-confirmed generalizations or well-designed experiments. For these books helped train us to use new descriptive and evaluative vocabularies: they gave us helpful new tools for reflection and deliberation. Bringing all these tools together in the way the positivists had hoped to bring them together, or refusing to use some of them because they could not exhibit proper credentials, came to seem pointless.

   Most of us philosophy professors now look back on logical positivism with some embarrassment, as one looks back on one's own loutishness as a teenager. But this is not how Wilson sees the matter. He says that "logical positivism was the most valiant concerted effort ever mounted by modern philosophers. Its failure or, put more generously, its shortcoming was caused by ignorance of how the brain works. That in my opinion is the whole story."

   Whereas the logical positivists hoped to unify culture by replacing unscientific claims with scientific knowledge, and to do so by isolating a method used to produce such knowledge, Wilson hopes to promote the unity of knowledge by showing the importance for the social sciences, the humanities, and the arts of what he calls "epigenetic rules," defined as "the inherited regularities of mental development that compose human nature," rules hard-wired into our brain in the course of its evolution.

   I have no doubt that there are such rules. It is possible that there are many more of them than we currently suspect, and also that when our knowledge of brain physiology improves we shall be able to do something like what the logical positivists failed to do. But this latter possibility seems to me rather faint. I was not persuaded by the rules Wilson cites: those which produce "the hallucinatory power of dreams, the mesmerizing fear of snakes, phoneme construction, elementary preferences in the sense of taste, details of mother-infant bonding," and the like. Such examples are hardly enough to show that social scientists, humanists, and artists should hasten to improve their knowledge of evolutionary biology, nor that they should confidently expect help from future developments in that field.

The main trouble with the argument for consilience is that we get no account of what the more integrated culture that its author envisages would look like, nor much reason to think that such a culture would be better than the one we have now. Wilson is convinced that the boundary between the humanities and the sciences needs to be blurred in somewhat the same manner as we blurred the boundary between chemistry and biology. But the reason for blurring the latter boundary is much clearer than the need to blur the former. Figuring out how littler and simpler things work helped us figure out how bigger and more complicated things work. But when we turn to questions about what to do with the top-level things (the human brain and the human sexual organs, the rich nations and the poor nations, the research programs of the various academic disciplines), it is not clear that our answers to such moral or practical questions will be improved by better knowledge of how things work.

   My positions on vexed intellectual questions (for example, the need for a more unified culture) or vexed political questions (for example, gay marriage) do not seem to rest on premises that natural scientists might someday correct. I have no idea how Wilson would go about tying in his own positions on these matters with his knowledge of cerebral or reproductive physiology. For it is with my brain as it is with my computer: my problem is what program to install in these things.

   I pick a program in blissful ignorance of how my computer embodies and executes programs. Since the human brain seems as indifferent to cultural differences as the machine is to my choice of program, there seems no reason why we cannot argue out such differences in blissful ignorance of how the brain works. It may be, as Wilson suggests, that there are biological reasons why some cultures are easier to establish or to preserve than others, just as there are hardware reasons why some programs are easier to write or to install than others. But we need more of an argument than he gives us for the claim that our choice of the sort of society to create, or of the kind of person to be, will be insufficiently informed until we have learned more about our brains. Unlike Wilson, I do not "find it hard to believe that had Kant, Moore, and Rawls known modern biology and experimental psychology, they would have reasoned as they did." I wish he had specified more fully just which results of these disciplines would have led these philosophers to change their ways.

   The idea that we should try to bring the social sciences together with the natural sciences sounds, at first blush, more promising than the idea of erasing the boundary between both and the humanities. But I think this is only because of an ambiguity in the term social science. Sometimes it means something like "behavioral science" and at other times something like "policy science." The books by social scientists that provide suggestions about what we should do, rather than predictions about what we will do, are closer to the border that separates their disciplines from the humanities and the arts than to the border that separates them from the natural sciences.

If the last few hundred years of human history have taught us anything, it is that the imagination of our ancestors has usually been inadequate to the achievements of their descendants. We have come up with many things that once seemed unimaginable: the rule of laws rather than men, nation-states whose citizens belong to many different religions, women holding high public office. So we have come to distrust the people who tell us that "you cannot change human nature"--a slogan that was employed against the education of women, interracial marriage, and gay liberation. I doubt that we should put more faith in natural scientists wielding this slogan than in the theologians and philosophers who did so.

   Of course, this point about the unimaginability of the future cuts both ways. Wilson could use it to argue that the unified culture of his dreams--a culture in which biology does for psychology, sociology, and political science what chemistry has done for biology--may well come into existence. Stranger things, to be sure, have happened. But Wilson's dream is not made more plausible when he says that "belief in the intrinsic unity of knowledge . . . rides ultimately on the hypothesis that every mental process has a physical grounding and is consistent with the natural sciences." I have no doubt that this hypothesis is true, but it simply does not follow that knowledge, or culture, should become more unified than it is. That is like inferring from the fact that every workable piece of software has a hardware realization to the conclusion that we should aim at One Big Unified Program.

    On one point, however, I quite agree with Wilson: there is no need to continue the tedious culture wars that C. P. Snow and Martin Heidegger, among others, have tried to incite. In The Two Cultures (1959), Snow claimed that scientists are naturally on the political Left, the side of human freedom, whereas littŽrateurs naturally sympathize with the authoritarian Right. This argument was absurd when Snow advanced it 40 years ago, and it sounds even sillier now. Heidegger's neo-Nietzschean conviction that our Baconian, technological culture has reduced our stature--made us moral and spiritual pygmies--is equally implausible.

   Wilson's book, however, by making similarly implausible claims about the need to unify knowledge, and by suggesting that it is the humanists who are blocking progress toward such unification, seems likely to reignite conflict. Like Snow, Wilson finds it shocking that many humanities teachers know nothing about natural science. He suggests that to neglect science is to neglect the Enlightenment, which is, he rightly says, the origin of most of the good things that have happened in the last couple of hundred years.

   But one can be utterly devoted to the Enlightenment's project of a decent life for all the inhabitants of the planet, a life as free citizens of a cooperative commonwealth, while remaining in brutish ignorance of how computers, brains, or anything else works. I know quite a few people of this sort. I also know some who entirely share this devotion to Enlightenment ideals but, having no taste for philosophy, poetry, or cultural politics, remain largely ignorant of all three. There will be no conflict between these two groups of people unless somebody stirs it up. One way to stir it up is by telling them that their traditional division of labor is misguided.