Working Title:

Explaining the Mind: Problems, Problems

by Stevan Harnad

The Feeling of What Happens

by Antonio R. Damasio

Harcourt Brace, 2000

hardcover, $TKTK; softcover, $15.00

A Universe of Consciousness

by Gerald M. Edelman and Giulio Tononi

hardcover, $TKTK; softcover, $17.00

The Mysterious Flame

by Colin McGinn

Basic Books, 1999

hardcover, $TKTK; softcover, $TKTK

The Cultural Origins of Human Cognition

by Michael Tomasello

Harvard University Press, 1999

hardcover, $TKTK; softcover, $TKTK

The Mind Doesn't Work that Way

by Jerry A. Fodor

MIT Press, 2000

hardcover, $TKTK

It has lately become fashionable in cognitive science to call the problem of consciousness the "hard problem," and the problems of meaning and language (and brain function and behavior) the "easy problems." Everything is relative. The "easy problems" may be easier than the "hard problem," but that does not make them any easier than most other scientific problems.

What, then, is the hard problem? It's as old as the mind itself, and it's probably lurking behind people's ideas about religion, and the immateriality and immortality of the soul. It has been pondered since the advent of philosophy, where it is usually called the mind-body problem. Unfortunately, the word "mind" is ambiguous in that context, and "body" is a misnomer. Some philosophers think it's more useful to call it the "mental-physical" problem instead, but even that doesn't quite do the trick.

The problem itself arises in trying to relate one kind of "thing" (mental things) with another

kind of thing (physical things). Everyone knows that physical things encompass more than just "bodies": They are made up of matter and energy, the stuff that physicists (and chemists and biologists and engineers) study and account for with their familiar functional, cause-and-effect explanations: the eye works by focusing light on the retina; the lake warmed up because the sun was shining. And everyone knows exactly what mental "things" are, too: They are what is going on in our heads when we are awake: thoughts, experiences, feelings.

The problem is: How is one to put those two kinds of things together: Are they both the same kind of thing? Are thoughts, experiences and feelings just matter and energy, somehow? If so, How? (And here I pause to let the reader test whether, mirabile dictu, he can provide a satisfactory answer to this hard question where everyone else so far has failed. . . .)

Telekinetic Dualism

vs. Decorative Epiphenomenalism

If the mental and the physical are not the same

kind of thing, what is the relation between them? It is clear that they are exactly correlated, but correlation is not explanation. How does the mental fit into the physical world causally? Is it a force, like gravitation? Some people, who embrace the supernatural in the face of the hard problem, reply "yes," and boldly proclaim the telekinetic power of the mind (rather like Uri Geller's spoon-bending, except that the process they are describing would be telekinetic even if one's fingers, unlike Geller's, were strong enough to bend the spoon: according to telekinetic theory, one moves one's fingers--and the fingers then do whatever they do--because one feels like it).

The trouble with such an easy solution to the hard problem is that it has some uneasy consequences: It is at odds with the laws of conservation of mass and energy, causal laws of physics that have mountains of evidence in their favor. To regard the mental as a telekinetic force, one has to believe, for instance, that things move because they are willed to move, not just because of the usual transfer of energy. And what is the source of the telekinetic force? That's anyone's guess, but it can't be just the brain, because the

brain, like the heart and the liver, is just that ordinary stuff: matter and energy, structure and function. (If the brain turns out to be the cause of all people's motions after all--in other words, if telekinesis really doesn't happen, as I suspect most readers of The Sciences would be willing to grant--it would never be true that one moves because one feels like it; it would just feel-like that was how and why one was moving.)

I will not pursue the telekinetic option any further (it is often called dualism), because, in exchange for "solving" the hard problem, it seems to raise even harder problems, pitting itself against all the rest of science. Suffice to say that none of the authors of the books under review would endorse telekinetic dualism. They are all committed to explanations that stay within the natural bounds of matter and energy, structure and function--bounds set by current theory and evidence in physics, biology and engineering. Yet one must admit that telekinesis certainly feels like the right explanation for the mind, what the mind does, and how. It's just that such an explanation does not fit with the scientific explanation of anything else--and so the exceptional character of the

explanation itself would stand in need of scientific explanation.

Three of the books under review try to take on the hard problem directly. Antonio Damasio is convinced that recent advances in understanding brain anatomy, physiology and neurology can offer new perspectives on the problem. Gerald Edelman and Giulio Tononi are equally sanguine about the insights gained from computational models of brain function. Colin McGinn, in contrast, does not try to solve the hard problem at all, but with an excuse: he argues that, though the problem does have a solution, the brain could neither find it nor understand it if such a solution miraculously came to be formulated.

The other two books under review, by Michael Tomasello and by Jerry Fodor, deal with language and meaning, respectively, topics so closely related to the problem of consciousness that its discussion would seem essential. Yet neither author ventures to take on the hard problem. Tomasello does not even mention consciousness. And Fodor thinks it would be futile to discuss it, but, unlike McGinn, he does not say why (he spends his

time instead trying to show why science may not even be able to solve some of the easy problems!). In the end, though, even Damasio and Edelman and Tononi make no headway in answering the hard question, because they beg it.

There are basically two ways to beg the question. One way is to change the subject, swap an easy problem for the hard one (but keep calling it the hard one anyway), and then solve the easy problem instead. The second way is to provide an easy but covertly inadequate solution, then interpret it as if it had solved the hard problem. Damasio pursues the first gambit; Edelman and Tononi adopt the second.

Damasio announces that he is not merely going to explain intelligence, language, brain function or behavior, because any one of them could be explained in principle even if there were no hard problem at all. And in fact, that point is an important distinction to make: If people had their familiar intellectual and linguistic capacities but were not conscious (no mental states, no thoughts, experiences or feelings), there would still be the "easy" problem of explaining those capacities in terms of brain function. But addressing that

problem would just be ordinary ("easy") science. I shall call that kind of an explanation a structural-functional explanation, or functional explanation for short. Functional explanations are perfectly compatible with the matter and energy explanations given by physics, biology and engineering.

What makes the hard problem hard is that giving functional explanations for mental states is not all there is to it: People are not just zombies with certain intellectual and linguistic capacities. We are conscious beings, that is, we do have mental states: thoughts, experiences, feelings. Whatever it is that makes such states mental I shall call feelings. [[Thus if we were nonfeeling zombies, there would be no hard problem.]] What makes the hard problem hard is the mysterious difficulty of explaining feelings functionally. So the mind-body problem is actually the "feeling-function" problem.

Why is it so hard (if not impossible) to explain feelings in terms of function? The reason is that a functional explanation is always a cause-and-effect explanation, showing how or why

something works the way it does. A functional explanation is fine for ordinary, nonfeeling matter and energy[[EDITOR'S NOTE (PGB): Double-bracketed material could be deleted to save space.

: the stuff investigated by physics, biology and engineering]]. But every time one tries to explain a feeling functionally, it turns out that the functional explanation alone can do the cause-and-effect job just fine [[(thank you very much!)]], and the feeling just falls by the wayside, unexplained.

Thus a functional explanation of pain might go something like this: It is useful for an organism's survival and reproduction to minimize tissue injury, to learn and remember to avoid what has caused injury in the past, to avoid contact between a currently injured body part and other objects while the part is still damaged, and so forth. The workings of the sensorimotor and neural machinery for accomplishing all this, including the computational mechanism that would do the learning, the remembering, the selective attending and so forth, could all be described, tested, confirmed and fully understood. Part of that system for

avoiding tissue damage is a signal that tissue has been injured: pain. And that signal, too, could, in principle, be functionally and structurally described. The only part that would remain unexplained is why pain feels like something: The functional explanation accounts for the functional facts, but the feeling is left out. And so it goes: every time you try to give a functional explanation of feeling, the feeling itself turns out to be functionally superfluous (unless you happen to be a telekinetic dualist!).

In short, we know that we are not nonfeeling zombies. The hard problem is explaining how and why we are not. And because how's and why's are purely functional matters, that would seem to leave only two possible ways to characterize feelings: (1) that they are merely "decorative" albeit nonfunctional epiphenomena, piggy-backing for some inexplicable[[, because nonfunctional,]] reason on certain biological functions; or (2) that feelings operate telekinetically (the position of the dualists). The hard problem is finding an explanation for feelings that is neither (1) nor (2). My own view is that this is simply impossible. How do the authors of the five books approach the


Damasio's Error:

Motions, Emotions and Unfelt Feelings

Damasio sets out determined not to beg the hard question. Even his title, The Feeling of What Happens, makes it clear that what he wants to take on is the problem of feeling, not something else. And his book does provide a great deal of new, insightful and illuminating data and theory about the areas of the brain correlated with feeling, particularly the feeling of the self, and about the remarkable ways in which those areas can atrophy or break down in states such as sleep, coma, epileptic automatism and akinetic mutism, the most primitive feeling-state of motionless muteness. Everyone is a zombie in deep, dreamless sleep; are we zombies in any of those more active states, too? Such questions and answers are fascinating, and the correlates between brain states and behavior are of great interest to the clinician, the victim of brain injury, the families of such patients and anyone else interested in the workings of the brain. But those are all "easy" problems. Do

Damasio's findings shed any light on the hard problem of how and why we feel at all?

Alas, they do not, and I think I can pinpoint where the question gets begged: Damasio is intent on providing a bottom-up explanation of feelings, from akinetic mutism to feeling-states of the highest-order. But explaining the variations along such a hierarchy is the easy part; the hard part is explaining how and why any of it is felt at all. The critical transition, in other words, is between nonfeeling and feeling, and that is the transition Damasio completely overlooks.

Instead, Damasio rests his hierarchy of feeling-states on a highly nonstandard (and, I think, incoherent) concept of emotion. On the face of it, "emotion" is just a synonym for a certain kind of feeling. (Other kinds of feelings include sensations, such as seeing something blue or hearing something loud; hybrid emotion-sensations, such as feeling pain; desire states, such as wanting something; psychomotor states, such as willing an action; and complex feeling-knowing states, such as believing, doubting or understanding.) But Damasio applies the concept of emotion in an equivocal way, in an attempt to

bridge the unbridgeable gap between nonfeeling and feeling. His bottom-level emotions are either just motions, or in other words movement tendencies and their underlying brain activities, in which case they are no kind of feeling at all. Or, worse, emotions are "unfelt feelings," which is a contradiction in terms. Either way, one is left just as clueless as before about how to bridge the gap between nonfeeling and feeling. Yet it is only by invoking such a blurred concept of emotion that Damasio gives the (illusory) impression of having made a successful transition from the unfelt to the felt.

Descartes (whom some people wrongly blame for the idea of dualism) was the subject of an earlier book of Damasio's, titled Descartes' Error. In that book Damasio argued that Descartes had mistakenly tried to separate what in the brain is inseparable: the psychic (mind) and the somatic (body). In the functional anatomy of the brain, Damasio went on, there is no such separation. I agree; but I must hasten to add that Damasio's point is irrelevant to refuting Descartes: after all, all of the brain, both structure and function, is "somatic"--that is, explained entirely by ordinary physical matter and

energy. And that's precisely the same error Damasio makes in The Feeling of What Happens, in focusing on the functional aspects of emotions. For the functional part of emotion, the somatic part, is indeed, as Damasio maintains, just motion! But the felt, or psychic, part is something else: something 100 percent correlated with brain structure and function, to be sure--but, again, correlation isn't explanation. Correlations need a causal explanation, and the only candidate explanation, namely telekinetic dualism, is a nonstarter. Tough luck.

Edelman and Tononi's Hermeneutics

Like Damasio, Edelman and Tononi set out in their book promising not to beg the hard question. Do they manage to fare any better? They are at pains to explain the difference between real seeing and, say, the activity of an optical transducer such as a photo-cell. It will not do, as they correctly point out, simply to declare that one's favorite functional mechanism "feels" any more than it will do simply to declare that an optical transducer "sees." In both cases the how and why of the

feeling itself must also be explained.

But then Edelman and Tononi go ahead and beg the hard, "feeling" question anyway. They describe some intriguing functional networks--"distributed, re-entrant ones"--which they suggest could have some powerful functional capacities (some already demonstrated experimentally, many of them not yet). They also describe how such networks are brainlike in many ways. That is all important and exciting stuff, but it is still all just functional. The nagging question still remains: How and why do the feelings come in (other than as the usual mysterious, unexplicated correlations)? [[Without an answer to that question, Edelman and Tononi's discussion is just an exercise in hermeneutics: the functional mechanism that correlates with a feeling is interpreted as the feeling itself, and thereby being the functional explanation of the feeling; whereas in reality it is merely the explanation of the functions that are mysteriously correlated with the feeling, nothing more.]]

The locus of the question-begging can be pinpointed here, too: Edelman and Tononi's network model is largely a mechanism for learning categories. An essential part of that mechanism is

the need for discrimination. And their treatment of discrimination is equivocal in just the way Damasio's treatment of emotions is.

To discriminate is to be able to tell things apart. Psychophysicists speak about JND, or just-noticeable-difference--the smallest sensory difference that people can feel. Feel? But of course psychophysics, being an ordinary functional science like all the others, really only deals with the smallest sensory difference people can detect and respond to. That could just as well apply to an optical transducer. The fact that it also happens to feel-like something when one detects those differences is another matter, and Edelman and Tononi's model comes no closer to explaining the how and why of that than an optical transducer does.

[[Two other points are worth making in passing about Edelman and Tononi: (1) They cast some of their argument in terms of another fashionable problem, the so-called binding problem: How does the brain manage to "bind" all its simultaneous sensations of an object into one unitary percept of that object? But would there be a binding problem at all if there were nothing it felt-like to

perceive an object--if the brain just went about all its functional business of moving, categorizing, discriminating without feeling anything while doing it? Might the binding problem be just another variant of the (hard) question of how and why people are not zombies? (2) I personally did not glean much insight from Edelman and Tononi's paraphilosophical koan, "being precedes describing."]]

McGinn: We Don't Have the Brains

Colin McGinn suggests that the reason our species must resort to question-begging or koans in the face of the hard problem is that people just don't have the brains to solve it. Now I will immediately concede that he could be right--but by the same token, the creationists could be right, too. There may be mysteries beyond the grasp of our intellects.

But why should the feeling-function problem be one of them? To make McGinn's suggestion into anything more than an arbitrary conjecture, one would have to answer a how-and-why question every bit as hard as the hard problem itself, namely, how

and why is the brain unable to solve the hard problem? McGinn unfortunately provides no hint of an answer to that question, leaving the reader not one whit less mystified than he was before McGinn asserted that the mystification is innate.

What is interesting about McGinn's position is his [[positive (though nondemonstrative)]] declaration that there is a reason the brain causes feelings (the reason just happens to be one that people are not equipped to grasp). As evidence, he gives examples of other kinds of things--things whose existence is hardly in question--that the brain is not equipped to grasp either. People cannot know, for instance, what it feels like to be a bat (with its extra sonar sense), any more than someone born blind can know what it feels like to see. But that's cheating! It is tantamount to saying that a feeling is simply missing from the human repertoire, and that feeling is: what it feels like to know.

To give his point some substance, McGinn would have to state the solution to the hard problem, as well as how and why it is the solution, even though it does not feel like the solution. He would also have to say how and why people are unable to grasp

the solution as being the solution. But, one might ask, why should the solution have such a bizarre set of properties? On the face of it, all that is required is a functional, how-and-why explanation of conscious feeling. Such explanations tend to be objective ones, which do not depend on how they feel to you, any more than the truth of a mathematical proof depends on whether or not it feels true to you. If there is indeed a functional explanation of feeling, it ought to be possible at least to state it (and test it, functionally), even if, because of the brain's limitations, such a statement would not dispel the attendant mystery about the hard problem from our minds.

But perhaps McGinn means something even stronger: Not just that human beings lack the sense to see that something is a solution to the hard problem even when it is staring us in the face, but that we even lack the means to state such a solution. But that would be very odd, because it would be a limit not just on the nature of the brain, but on the expressive power of language and mathematics (both of which, though rooted in the brain, have universal, brain-independent powers, too): I may not be able to feel what it is like to

be a bat, but surely I should be able to state all the functional facts about it (in fact, that's exactly how the bat's sonar sense is understood, and there is absolutely no mystery there, just the bat's feeling that we know we lack).

No, I don't think McGinn's conjecture helps with the hard question at all: If the question is, how and why do we feel, his reply that we are not equipped to know simply raises another question, just as hard: How and why not?

Before leaving the hard problem and moving on to the two books that address easier problems, I will venture an answer: It is not because we have the wrong brains. It's because of the nature of functional explanation and the nature of feeling. The only alternative to telekinesis (in which feelings would have an independent causal power of their own) is that feelings do not have an independent causal power of their own. They just are. (Their existence is not in dispute.) Moreover, they pose no problem to the rest of science if they are simply side-effects of matter and energy, structure and function, not causes in their own right.

Make no mistake: no one is the less mystified

by the conclusion that the "function" of feelings is merely decorative (a position called epiphenomenalism), but at least it moots any further how-and-why questions. It implies that the hard problem is insoluble, that telekinesis itself is false, and that feeling has no (nontelekinetic) functional explanation (hence it is inexplicable). [[And one is still left with the sense of mystery about how and why this should be so--a mystery that could perhaps only be dispelled if we did have an extra sense, a telepathic sense, of the way matter-energy-structure-function causes feeling.]] [[But that hypothetical sense is just as self-contradictory, hence impossible, as a functional explanation of feeling, because of the essentially first-person nature of feeling: The only feelings you can feel are your own. ("I feel your pain" is just a metaphor.) So any "telepathic" sense I had of how nonfeeling causes feeling could only be an illusion. I can feel only what I feel, not how I (or anyone else) feel(s).]]

Tomasello: Pantomime vs. Propositions

The question Tomasello is trying to answer is

unapologetically one of the "easy" ones: How and why does our species, and no other, master language? In the past, other theorists have begged the question of consciousness by suggesting that having consciousness and having language are somehow one and the same thing, but Tomasello will have no part of that view. He recognizes that animals--particularly nonhuman primates and other mammals--not only have feelings but that they are also very smart. So in many ways the question about language is: How and why do people differ from other animals in that respect? What is the functional specialization that makes people capable of language, and other animals incapable?

To answer that question Tomasello studies the behavioral, social, conceptual and communicative capacities of apes as well as those of children, further charting them in children both before and after the acquisition of language. His comparative studies point to a few critical capacities: the capacity to imitate others; the capacity to "mind-read," or in other words, to sense what others are seeing, wanting or thinking; and the capacity to monitor and coordinate joint attention with others: to sense that both of you are looking

at or thinking about the same thing, and to sense that the other one senses that too. (Damasio's mechanisms for the sense of self would come in handy here). No nonhuman species has that set of capacities in full, and not even the human child does until the onset of language. Tomasello concludes that precisely those capacities make up the functional basis of language.

But do they? (For the moment, I will leave aside the separate question of the functional basis of grammatical capacity--another "easy" problem.)I would like to suggest that they do not. Human language is, among other things, the capacity to express any proposition with a string of symbols--"The cat is on the mat," "Feeling cannot be explained functionally," "2 plus 2 is 4"--plus the capacity to understand symbol strings as expressing propositions.

But if you look closely at the capacities Tomasello has singled out (and even if you design a functional model that implements those capacities), you will find that you have a mechanism capable of producing and sharing social pantomime. Such a mechanism could act out present and future scenes, draw people's attention to this or that, share all

the kinds of knowledge that can be shared by this kind of joint activity--but it could not provide a clue about how to get from pantomime to propositions. Even acting out the cat's being on the mat is simply that: a pantomime of the cat on the mat, in much the same way that the actuality of the cat's being on the mat is the same pantomime.

In short, entities with Tomasello's functional capacities remain in the analog world of events, and copies and re-enactments of those events. Such capacities well be necessary preconditions for language. But there is no language proper until one makes the transition from the analog world of social imitation to the arbitrary, symbolic world of propositions.

[[Perhaps Tomasello's functional resources need to be augmented with Edelman and Tononi's: If their category-learning network has the power they say it has, it should be able to learn to detect and identify cats and mats and "on-ness." If it can also string those concepts into propositions that describe events and can be construed as either true or false, the functional substrate for language capacity may indeed be at hand.]]

Fodor's Skepticism about Explaining the Mind

Building propositions out of imitation or even category-learning, however, is an enterprise about which our last author, Jerry Fodor, is somewhat skeptical. To understand what Fodor is driving at, you have to know where he is coming from. Fodor, like McGinn, is a philosopher (in fact they are now both at Rutgers University in New Brunswick, New Jersey), but his work is in part inspired by the monumental grammatical work of the linguist Noam Chomsky of MIT. Chomsky showed that much of the human capacity for grammar, rather than being learned, arises from a complex inborn structure in the brain. Furthermore, that inborn "universal grammar," or UG, probably did not evolve the way fins or wings did: instead, UG is somehow an intrinsic part of the structure of matter, or possibly even a necessary part of the eternal Platonic world of logic and mathematics, constraining matter whenever it is configured into a mechanism capable of language.

Now this view of Chomsky's is highly controversial, but it has a great deal of evidence supporting it: It does look as if UG isn't and

cannot be learned by the language-learning child (as Chomsky has long pointed out, the trial-and-error possibilities are far too large, and the child's actual learning time and experience far too small); for similar reasons, it is hard to imagine how UG could have evolved in the usual way (but that conclusion is perhaps not as firmly based on evidence as the fact that UG cannot be learned in childhood).

Fodor, impressed by the innateness of one function of the mind, UG, generalizes to other functions that go far beyond the evidence for UG: Fodor thinks that most categories ("cat," "mat," "object," number" and so forth) are innate and unlearned too, just as UG is. All that children learn is what names to call them; their meanings are already innately in their heads, like place-holders merely waiting for labels. If this assertion is true, it is bad news for Edelman and Tononi's category-learning networks, because it leaves them precious little to do: Most of the category structure of the world would somehow have to be built into them in advance.

But is there any reason to believe Fodor's assertion is true? Is there any evidence that there

are not examples enough, and time, for children (and adults) to learn all the kinds of things there are in the concrete and abstract world by trial and error, guided by feedback indicating when they get it right and wrong? I think there is no such evidence. But then why does Fodor believe that what is true of grammar might be true of meaning too?

I think the answer is related to yet another ("easy") problem, the symbol-grounding problem: Symbols alone do not mean anything. Ignorant of Chinese, you would look in vain for the meaning of any Chinese word in a Chinese-Chinese dictionary: It's all in there, and yet it isn't! You look up a definition, and it's just more meaningless symbols, even though, for a Chinese speaker who does not know the meaning of that particular word but does know the meaning of the words used to define it, it's enough to convey the new meaning.

The example illustrates at once the power and the limitation of language: In principle, you can find out anything and everything from strings of words expressing propositions, but you can't start from scratch: Some of the words have to be "grounded" in something other than just more (meaningless) words. How are those basic words to

be grounded? Edelman and Tononi's networks, linked to the world through sensors and effectors, sound like a good start, although one would be well-advised to build in the functions Damasio describes for internal sensorimotor maps and the self, as well as the functions Tomasello describes for social communication.

Such a system would then ground some of its symbols directly, in the capacity to detect, discriminate, categorize and manipulate the things they stand for in the outside world. Other symbols could then be grounded indirectly, through propositions that define them in terms of already grounded symbols.

Fodor thinks that kind of mechanism is a nonstarter, for pretty much the same reason that the "associationism" of seventeenth-century philosophers was a nonstarter: Thought and meaning arise not merely through the association of "ideas." Thought has structure over and above mere association in time and space. Symbols and computation can perhaps capture some of the structure of thought, but Fodor doubts that they can do the whole job. His doubts are based in part on worries about "holism" (the view that symbols

are local things, but meanings are not) and in part on "abduction" (how can a symbol system find the best theory to explain any set of data unless the answers are all already built into it in advance?)

[[(It should be added that Fodor seems to have little more faith in the explanatory usefulness of "modules"--despite the fact that he himself was responsible for popularizing the notion--than he does in nets or symbols [or brain function, for that matter]. We can define modules, in a theory-neutral way, as functionally independent components of a system, components whose design can be understood and modeled on their own, in isolation from the rest of the system. Perhaps because Fodor's own notion of modularity was inspired by UG [which was originally considered by Chomsky to be a functionally independent component of our language mechanism], the definition of "module" has been saddled with so many additional arbitrary stipulations--they must be innate, they must be "informationally encapsulated," they must not be influenced by what a person knows--that the word really has lost all its usefulness.)]]

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Are there grounds for Fodor's skepticism about the only explanatory resources that cognitive science has at its disposal? It is certainly true that cognitive science has not even come close to solving any of its "easy" problems, such as explaining the functional basis of language or meaning or any other lifesize piece of human intellectual capacity or brain function. But it's also hard to know how fast cognitive science ought to be explaining the mind, based on scientific track records elsewhere. Tononi and Edelman have to be given the time to demonstrate whether or not their nets can do what associationism could not. Their nets are, after all, operating on sensorimotor and symbolic inputs, not "ideas," (whatever those are).

And if symbols have their limitations, they also have their powers. No one can say in advance what hybrid systems can or cannot accomplish if their symbols are grounded in the sensorimotor world via category-learning networks. Changing the definition of just one word in a dictionary already propagates "holistically" to every other definition in the same dictionary. Change the sensorimotor

grounding and the holistic effects could be even more dramatic.

But if what you want to know is how and why it feels like something to have and exercise all those remarkable functional capacities, I am afraid you will be disappointed. That is one unsolved mystery we all will just have to learn to live with.

Stevan Harnad is a professor of cognitive science at the University of Southampton in England.