Philosophy

Are zombies really possible? Dennett sees noreason to think so. Rosenberg disagrees, and heaims to bolster and extend the following kind ofargument in support of the possibility of zom-bies: consider a body somewhat like ours, butcontrolled remotely by radio communicationwith a giant computer. Ordinary human beingsmay be extremely complex, but it is plausible tosuppose that our complexity could, at least inprinciple, be replicated by a monumentallycomplex computer. Putting these two thoughtstogether, there could, in principle, be creaturesbehaviourally indistinguishable from us butwith computers for “brains”. Would they be con-scious? Would they feel pain, experience ourspectrum of colours, and so on? The naturalreaction is: Who knows? How could we tellwhether exactly duplicating the human brain’sfunctional capacities in different “hardware”would generate qualia? It is an open question,one that we human beings might never be ableto answer, were we actually confronted withsuch creatures. Rosenberg believes that thisreaction represents a positive insight into thenature of qualia: the presence or absence ofqualia within a given computer-brain is amerely contingent matter. One wants to say:God could make computer-brains with qualia,and ones without. But then it should be amerely contingent matter whether other com-plex objects generate qualia – including objectsthat look, from the outside, just like our brains.Of course we know that our brains do – weknow this “from the inside”. But if it is a contin-gent matter whether non-organic beings haveconscious experience, it must be a contingentmatter whether organisms more closely resem-bling us have conscious experience. So zombiesare possible; or so the argument goes.Those who reach this conclusion (“theZombic Hunch”, as Dennett calls it) must rejectphysicalism. “God’s decree” may settle all thefacts describable within a “final physics” thatmentions no mentality; nevertheless, whetherthere is phenomenal experience would remainan open question. To settle the matter affirma-tively, the creative act must include more – forexample, the enforcement of extra laws linkingbrain states and qualia.Antecedents of the zombie argument againstphysicalism may be found in Locke and Leib-niz, and Rosenberg’s use of them owes much toDavid Chalmers (see The Conscious Mind,reviewed in the TLS, June 21, 1996). But headds an interesting twist. He makes use of a par-ticular sort of computer to serve as the brains inhis story. John Conway’s “Game of Life”, famil-iar since the 1970s, is a “cellular automaton” (amini-version can be downloaded at http://www.bitstorm.org/gameoflife/standalone/). It con-sists of a two-dimensional grid, like a chess-board. Individual squares may be in one of twostates: “red” or “black”, for instance (a Game-world need not use red and black as the differ-ence between its two states: any pair of colourswill do, or indeed any pair of distinct, space-per-vading qualities). The “Game” is a simple set ofrules determining the “next state” of the grid.Roughly, squares that are nearly surrounded bysquares of the other colour will switch states, aswill squares that are nearly surrounded by theirown colour. Otherwise, a square retains its col-our. These deterministic “laws” govern the evo-lution of the two-dimensional chessboardworlds. Surprisingly, “life”, of a sort, is possi-ble even in worlds with the Game’s simple phys-ics. Stable groups of red or black squares can bedesigned so as to “move about”; stable

“machines” can be built to create them. Theactivities of complex “life-forms” can be mim-icked in the Game’s “matter”. A computer ofany imaginable complexity could be built in theGame, given grid enough and time.Suppose astronauts on an intergalactic voyagefind their path blocked by a Game-governed“flatland” filled with two-dimensional butapparently intelligent creatures. The astronautsmight, for instance, bump into an invisiblegrid, with positively and negatively chargedsquares. But Rosenberg asks us to imaginesomething stranger: a Game-world in whichthe squares do not differ in colour, charge orany other independently conceivable property.Instead, the difference is “bare” or “brute”.Imagine that the inhabitants of the invisible gridgive the astronauts a mysterious device ena-bling them to tell whether squares are “on” or“off”. When the astronauts ask about the differ-ence between “on” and “off”, they are told that“on” means “not off” and “off” means “not on”.If the difference is genuinely brute, there is nomore to say.Rosenberg takes the “Zombic Hunch” to bestrongest in the case of the flatlanders in such aworld: a Game-world built upon bare differ-ences is utterly devoid of qualitative features,phenomenal or otherwise. The rich variety ofphenomenal colours, flavours and smells wouldnot be found in a world where all differencesboil down to complex combinations of “on”and “off”. With this conclusion in hand,Rosenberg argues that the physics of the actualworld is consistent with the fundamentalphysical differences being “bare” or “brute”.Physics merely describes “a network of effec-tive dispositions, with each element typedaccording to its place in a network of relationsto other such dispositions”. As Bertrand Russellput it, “physics . . . reveals only certain mathe-matical characteristics of the material withwhich it deals. It does not tell us anything as tothe intrinsic character of this material”.Rosenberg’s idea, then, is that a completedescription of the matter of our universe in phys-ical terms might as well be a description of aGame-world. And if this is right, there couldhave been creatures indistinguishable from us,so far as physics is concerned, but lacking phe-nomenal experience altogether. In other words,there could have been zombies.A flatland with brute differences betweensquares would, in effect, be a physical worldwith no intrinsic differences among its ultimateparts. Is such a world really possible? Somewill say, “No”: if a Game-world with a certainpattern is to be concretely realized within aplane, there must be intrinsic differencesbetween parts of the plane that can play the“on” and “off” roles in the Game’s simple“physics”. The fundamental building blocksof any material world must have “insides”,some kind of intrinsic nature. Surprisingly,Rosenberg does not really dispute this – whichrather undermines his use of the Game-worldto bolster our Zombic Hunch.Rosenberg’s positive theory of mind–matterrelations does not require that brute physicaldifferences are a genuine possibility, only thatphysics does not pin down the intrinsic natureof fundamental properties. In that case, theymight even be phenomenal properties, for allphysics has to say about it. And that’s exactlywhat Rosenberg claims they are. Quarkshave little “experiences” with a “qualitativecharacter very alien to us”; they may be like“little fireflies in the night supporting brief

flashes of sensation as they interact”.Rosenberg is not the only contemporaryphilosopher defending “panpsychism” – thethesis that all matter is suffused with conscious-ness. Thomas Nagel wants panpsychism backon the table, as a viable alternative to orthodoxmaterialist metaphysics. Similar views havebeen advanced, more or less tentatively, by anumber of philosophers, including DavidChalmers, Michael Lockwood, Peter Unger,Galen Strawson, David Ray Griffin andWilliam Seager.Dennett asks a question all panpsychistsmust answer: How does a “smidgen” of simpleconsciousness in the tiny parts of a brain add upto the complex consciousness we enjoy? A nor-mal person’s sensory experience is not the sumof a vast congeries of “brief flashes of sensa-tion”. One also wonders: are the propertiespanpsychists attribute to tiny particles phenome-nal in name only? Phenomenal propertiesbelong to experiences; but aren’t reflection andattention necessary for experience? And surelyelectrons are not capable of complex thought.The second half of Rosenberg’s book is aresponse to such challenges. He proposes anoriginal (perhaps too original) theory of causa-tion, according to which human consciousnesshas much in common with the properties phys-ics attributes to inanimate matter. It is here thatRosenberg passes completely into the land ofpure metaphysics, offering a theory of “naturalindividuals” and their causal interrelations torival that of Whitehead in complexity – and,some will think, obscurity. Even philosopherssympathetic with Rosenberg’s project maywell have trouble “getting inside” his system,despite the evident care with which it is con-structed. Everything depends upon his notion ofa “receptive connection” that “binds” individu-als – a causal relation peculiar to his theory, andhard to understand from other perspectives. If adialogue should open up between Rosenbergand those defending more familiar theories ofcausation, the result would likely shed lighton what is now a darkly forbidding edifice.Dennett’s verdict on a project like Rosenberg’swill not await the outcome of a polite dialogueamong metaphysicians, however. Only a crack-pot would erect a theory of consciousness uponthought experiments, on his view, for they canelicit nothing but groundless “hunches”.Zombies are extreme; one may be forgivenfor agnosticism about their credibility. Butthere are less bizarre thought experiments threat-ening physicalism, and Dennett is as disdainfulof the “hunches” they elicit as he is of the“Zombic Hunch”. Do others see colours inquite the same way as oneself? Could someoneelse’s experience of the colour spectrum be sys-tematically inverted relative to one’s own – redobjects appearing violet, orange objects appear-ing indigo, and so forth? The colour inversion“hunch” is stronger than the Zombic Hunch: itseems easy to imagine creatures just like us atthe microphysical scale, but with inverted col-our experience. Perhaps such inversions couldnot happen to us, given the physics (andpsycho-physics) of our world; but many philos-ophers are inclined to take the conceivability ofinversion as reason to suppose that such inver-sions are possible in a more abstract sense –“God had a choice” whether to correlate brainstates and qualia in the way he did. But thenphysicalism is false: settling the facts that phys-ics can describe would leave the phenomenalfacts up in the air.As famous as zombies, there is the story

Frank Jackson tells of a mythical neuroscientistcalled Mary. Although confined all her life toan entirely black-and-white environment, Marylearns everything physics, biology and cogni-tive psychology can possibly tell her about theway visual information is encoded and utilizedby the brain. Can Mary learn the entire physicalstory about colour perception, without yetknowing what the experience of red is like?Suppose it is so much as possible for her toknow all the physical facts while not knowingsome facts about human experience, even withgod-like powers of ratiocination. In those cir-cumstances, seeing (or even vividly hallucinat-ing) a red object would teach her somethingnew about consciousness – something shecould not deduce from the physical facts alone.So the physical facts are not all the facts.These stories might seem possible, saysDennett; but that “seeming” is evidence ofnothing but our own gullibility. Dennett asks usto imagine that someone has the followinghunch: “If you burp, sneeze and fart all at thesame time, you die”. Should we take this wildguess seriously, as a fact of biology? Of coursenot! According to Dennett, our pre-scientificconvictions about the nature of experience areon all fours with this idiotic hunch. Weshould wait until science tells us the real storyabout the mind; until then, our common-senseconvictions about consciousness should bedemoted to the status of wild guesses, with nopresumption in their favour.In effect, Dennett turns traditional empiricismon its head. The old-fashioned empiricist saysthat science brings hypotheses before the tribu-nal of sensory experience for confirmation or fal-sification. Dennett puts the judges on trial: every-thing we say about our awareness of colours,sounds, smells, etc is, as likely as not, unreliableconfabulation. None of it should be accepteduntil independently confirmed by impersonal sci-entific investigation; and the scientists whowould study consciousness are solemnly warnednot to slip into the habit of trusting even theirown judgements about what experience is like.Sweet Dreams is a sequel to Dennett’sConsciousness Explained (1991, reviewed inthe TLS, August 21, 1992) – a book that,although warmly received by a broader reader-ship, was roundly criticized within philosophi-cal circles. Non-philosophers may lose patiencewith Sweet Dreams, since it is simply a series ofreplies to Dennett’s philosophical critics. Buthis critics will find their patience tried, too.There are few ideas or arguments that were notset forth in the earlier book, and Dennett rarelydescends to the level of detail philosophers willexpect; most chapters were lectures, and retaina breezy informality. Although his prose dis-plays the dash and directness for which he isjustly famous, these strengths diminish inimportance in a book ostensibly aimed at spe-cialists. Many passages are marred by the blis-tering polemics and invective for which he isequally famous. Such lapses are understanda-ble. Dennett can barely bring himself to talkabout zombies and their ilk; it triggers his“giggle reflex” and his “gag reflex”. Evidentlyit is difficult to maintain a measured tone whendiscussing work one finds alternately laughableand sickening.The complexity and originality of Rosen-berg’s book make it hard to be sure how impor-tant its defence of qualia will prove to be, in thelong run. It is much clearer that, whateverDennett’s contribution to the zombie wars, itwas already made in Consciousness Explained.

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