P1:JZP 0521855310pre CUNY806B/Baker 0521855310 April30,2007 7:39 Alvin Plantinga Edited by DEANE-PETER BAKER UniversityofKwaZulu-Natal v CAMBRIDGEUNIVERSITYPRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University Press The Edinburgh Building, Cambridge CB28RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521855310 © Cambridge University Press 2007 This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2007 ISBN-13 978-0-511-28940-8 eBook (EBL) ISBN-10 0-511-28940-5 eBook (EBL) ISBN-13 978-0-521-85531-0 hardback ISBN-10 0-521-85531-4 hardback ISBN-13 978-0-521-67143-9 paperback ISBN-10 0-521-67143-4 paperback Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 8 Plantinga’s Replacement Argument PETER VAN INWAGEN INTRODUCTION AlvinPlantingahasrecentlyturnedhisattentiontomaterialism.Morepre- cisely, he has turned his attention to the thesis that philosophers of mind call materialism.1 This thesis can be variously formulated. In this essay, I willtake“materialism”tobetheconjunctionofthefollowingtwotheses: (1) Human persons – what human beings refer to when they use the first-person-singular pronoun – are substances. They are substances in the strict and philosophical sense: They persist through time, retaining their identities while changing various of their accidental properties;2 they are notgrammaticalfictions;theyarenot“modesofsubstance”;theyarenot logicalconstructsonshorter-livedthings(theyarenotentiasuccessiva);they are not abstract objects (they are not, for example, things analogous to computerprograms);theyarenoteventsorprocesses.3 (2)Thesesubstances,thesehumanpersons,arewhollymaterial.They are (if current physics is to be believed) composed entirely of up-quarks, down-quarks, and electrons, so related by the electromagnetic and color forces as to compose matter in its solid, liquid, and gaseous phases. They are, in two words, living organisms – or, if not whole living organisms, thenpartsoflivingorganisms(humanbrains,brains-plus-central-nervous- systems,brainstems,cerebralhemispheres,cerebralcortices–orperhaps even luz bones or tiny, almost indestructible material things unknown to physiology...).Theyhavenoimmaterialpart.4 Plantinga’s position as regards materialism can be summed up in the words of President Calvin Coolidge’s well-known summary of the preacher’spositiononsin:He’sagainstit.Thatistosay,henotonlyrejects materialism, not only thinks it false, but thinks it of great – as one might say – human importance to convince his philosophical audience that it is false.Inthatrespect,Plantinga’spositionvis-a`-vismaterialismisunlikemy positionvis-a`-visdualism(thatis,theconjunctionofthesis1andthedenial ofthesis2).5 Ithinkthatdualismisfalse,butIdon’tthinkit’sparticularly 188 P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 Plantinga’sReplacementArgument 189 important–inthematterofhowhumanbeingslivetheirlives–whether otherssharethisbelief.6IfthiswereanotherpaperaboutPlantingaonmate- rialism,Imighttrytoconvincemyreadersthathewaswrongtothinkthat the question whether we are material things was of great “human impor- tance”–aquestionwhoseimportancewascomparableto,say,theimpor- tanceofthequestionwhethermaterialisminthestrongsensementionedin note1istrue,orthequestionwhetherhumanpersonsaresubstancesinthe strictandphilosophicalsense,orthequestionwhetheranymoraljudgments areobjectivelytrue,orthequestionwhetherhumanpersonssurvivedeath. Inmyview,thequestionwhetherhumanpersonsarematerialisindeed“an importantphilosophicalquestion”inthesenseinwhich,say,thequestion whether there are Platonic universals, or the question whether causation canbeanalyzedintermsofconstantconjunction,areimportantphilosoph- icalquestions.Butwephilosopherscanperhapsforgivenonphilosophersif theyarenotmuchinterestedineitherofthesetwo“important”questions; itismuchhardertoforgivethem–itismuchhardertounderstandthem– if they are not interested in the question whether “the cosmos is all that there is or was or ever will be,” or the question whether they will have a postmortemexistence. Thisisnotthatpaper.Mybusinesshereiswithamuchmorenarrowly defined and technical issue. I propose to examine a certain argument of Plantinga’s,anargumentforthefalsityofmaterialism,anargumenthecalls “thereplacementargument.”7 THEREPLACEMENTARGUMENT 1 Ibeginwithastatementoftheconclusionofthereplacementargument: Iamnotidenticalwithanymaterialsubstance;thatistosay(sincewe arepresupposingthatIamasubstance),Iamanimmaterialsubstance. Thereplacementargument,likethecentralargumentofMeditationsonFirst Philosophy,isconductedinthefirstperson.Plantinga’stextisbotharecord ofAlvinPlantinga’sgoingthroughtheargument“forhisowncase”andan invitationtoeachofhisreaderstogothroughthesameargument(mutatis mutandis) for his or her own case. In my presentation of the argument, I will go through the argument for my own case: The pronoun ‘I’ in the statementoftheconclusionoftheargumentandinthepresentationofthe P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 190 PetervanInwagen argumentinthesequelreferstome.Whenonehasgonethroughtheargu- mentanddiscoveredthatoneisnotidenticalwithanymaterialsubstance (Plantinga contends), one will see that anyone else could go through the samechainofreasoningforhisorherowncaseanddiscovertherebythat he or she is not identical with any material substance. Having seen that this is so, one will, of course, conclude that no human person is identical with any material substance – that every human person is an immaterial substance. I am willing to grant that if Plantinga’s reasoning (adapted to myowncase)convincesmethatIamnotidenticalwithanymaterialsub- stance, it should convince me that every human person is an immaterial substance.Iwill,therefore,consideronlythefirst-personchainofreason- ingthatissupposedtoconvincemethatIamnotidenticalwithanymaterial substance. The first step in this chain of reasoning is intended to lead me to the conclusion that I am not identical with a certain material substance, my body.OnceIhavereachedthisconclusion(Plantingacontends),itwillbe evidenttomethat,foranymaterialsubstance,aparallelchainofreasoning would establish the conclusion that I was not identical with that mate- rial substance: that I was not identical with my brain, my brain-plus-my- central-nervous-system, my brain stem, one of my cerebral hemispheres, my cerebral cortex, and so on.8 I will grant that if one application of the replacementargumentprovesthatIamnotidenticalwithmybody,other, exactlyparallel,applicationswouldprovethatIwasnotidenticalwithany othermaterialsubstance. Iwillthereforeconsideronlytheargumentfor theconclusionthatIamnotidenticalwithmybody.(And,anyway,Iamone ofthosematerialistswhobelievesthatoneisidenticalwithone’sbody–ina senseof‘one’sbody’thatIshallspelloutinamoment.I,infact,believethat noneoftheotheritemsintheforegoinglistof“materialperson-candidates” exists.)10 Hereisthegeneralstrategyoftheargument.Iamtoconsider(guided byPlantinga’sstatementoftheargumentforhiscase)acertainimaginary episode or adventure – imaginary but possible – that I survive and during whichmybodyceasestoexist.AndIamtoconcludefromthepossibilityof thatimaginaryadventurethatIamnotidenticalwithmybody.Icertainly havenologicalobjectiontothisdialecticalstrategy.Ifitisindeedpossible for me to survive my body’s ceasing to exist, then to assert (in the face of thispossibility)thatIamidenticalwithmybodywouldbetodenyavery attractivemodalprinciple:thatx y x y,or,inplainEnglish,that = →∼♦ $= athinganditselfcannotpartcompany.11 (Similarly,ifsomeonewantedto convincemethattheMorningStarwasnotidenticalwiththeplanetVenus, and if that person proposed to prove this to me by asking me to consider P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 Plantinga’sReplacementArgument 191 animaginary–butpossible–astronomicalcatastrophethatdestroyedthe planetVenusandlefttheMorningStarunscathed,Ishouldhavenological objectiontothisstrategy.)Ofcourse,Ibelievethatanyapplicationofthis strategywillyieldanargumentwithafalsepremise–almostcertainlythe premise that the imagined adventure is a possible adventure – for, as I have said, I believe that I am identical with my body, and that conclusion follows jointly from this belief of mine and the obvious logical validity of the proposed argument. But that is no reason to refuse to consider the argument: For all I know, considering the imaginary adventure on which theargumentturnswillconvincemethatitismoreplausibletobelievethat that adventure is possible than it is to believe that I am (as I have always supposed)identicalwithmybody. Thequestiononwhichthecogencyofthereplacementargumentturns, therefore,isthefollowing:IstheadventurePlantingadescribespossible?– or,morecautiously,isitmoreplausibletosupposethatitispossiblethan itistosupposethatIamidenticalwithmybody? 2 I proceed to a statement of the replacement argument for the conclusion that I am not identical with my body. I begin with a description of the imaginary-but-possibleadventurethat(ifPlantingaisright)Ishouldsurvive andmybodywouldnot. Following Plantinga’s procedure in laying out the description of his adventure,Ifirstgivemybodyapropername:Isay,“Let‘B’beaproper name of my body.” But this thing I am supposed to do raises a question: WhatdoImeanby‘mybody’?Well,a(human)bodyis,Isuppose,aliving human organism – a thing that a biologist would classify as a member of thespeciesHomosapiens.ButwhatdoImeanwhenIsayofacertainbody, acertainlivingorganism,thatitismybody?Thisisnotatrivialquestion, since a definition of ‘my body’ that one philosopher favored might well be rejected as tendentious by other philosophers. For example: ‘the body withwhichIinteractcausally’(giventhatathingcaninteractcausallyonly with things other than itself). In “Philosophers and the Words ‘Human Body’,”12 Icontendedthatitwasnotpossibletodefine‘x’sbody’inaway that was neutral with respect to all historically important theories of the person-body relation – I contended, that is, that any possible definition of ‘x’s body’ would presuppose the truth or the falsity of at least one of thehistoricallyimportanttheoriesoftheperson-bodyrelation.Forpresent purposes, however, it will suffice to have a definition of ‘my body’ that is neutral with respect to dualism and materialism (with respect to the P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 192 PetervanInwagen affirmation of 1 and 2, on the one hand, and the affirmation of 1 and the denialof2ontheother).Andsuchadefinitionispossible: Mybody thelivinghumanorganismsuchthatitispossibleformeto =df bring about changes in that organism without bringing about changes in any other organism (other than such organisms as it may have as proper parts)–andwhichissuchthatcausingchangesinitcancausechangesin meandinnootherperson.13 Thisdefinitionisnot“neutralwithrespecttoallhistoricallyimportantthe- oriesoftheperson-bodyrelation,”foritpresupposesthefalsityofepiphe- nomenalismandoccasionalism(thatis,thethesisthatIhaveabodyinthis sensepresupposesthefalsityofboththesehistoricallyimportanttheories). Butitis,Ibelieve,neutralasbetweendualismandmaterialism.B,therefore, istobeunderstoodasapropernameforacertainlivinghumanorganism, thatlivinghumanorganisminwhichIcanbringaboutchanges“directly.” The adventure that is central to the replacement argument is, as one mighthaveexpected,anadventurethatinvolvestherapidreplacementof variouspartsofmybody.Theargumentcomesintwoversions,a“macro- scopic”versionanda“microscopic”version.Intheformer,thepartsofmy body that are rapidly replaced are largish, visible parts like my hands and feet and my left cerebral hemisphere. In the latter, the parts are smallish, invisible parts – atoms, perhaps, or cells. I will consider only the macro- scopicversionoftheargument.(Iwilllaterbrieflyexplainwhyitwillnot benecessaryformypurposestoconsiderthemicroscopicversion.) Here, then, is the macroscopic version of the replacement argument. Wesupposefirstthat,forsometimenow,mybrainhashadacertainodd property: At any given moment, one of my two cerebral hemispheres is “dormant” and the other “active”; at any given moment, the hemisphere thatisactiveatthatmomentisthen“doingallthatabrainordinarilydoes”; atmidnightofeachday,allthe“relevant”“data”or“information”(Irepro- ducePlantinga’sscare-quotes)thatwasthenstoredortokened(orwhatever the word should be) in the active hemisphere is copied to14 the dormant hemisphere; the dormant hemisphere then becomes active and the active hemisphere dormant. If I am awake when this rather complex event hap- pens,Ishallnotnoticeit.AnytrainofthoughtthatImaybeengagedinat the time will proceed without interruption. The first part of that train of thoughtwillbetokenedinonecerebralhemisphereandtheremainderin theother,andthe“hemisphereswitching”willhavenophenomenological consequenceswhatever. I do not know whether the recurring sequences of events that are entailed by my brain’s having this “odd property” are physically possible. P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 Plantinga’sReplacementArgument 193 And I do not know whether, if they are possible and if they were actu- allytooccur,theywouldhavethephenomenologicalconsequences(orlack thereof)thatareclaimedforthem.ButIaminclinedtothinkthatPlantinga is right to suppose that they are at least metaphysically possible and that heisrighttosupposethatIshouldnoticenothingifoneofthemoccurred whenIwasawake(thatthesequenceofeventswouldbethephysicalcor- relateofasingle,unifiedepisodeofconsciousness).Atanyrate,Iwillnot disputeeitherofthesethings. Wenowconsidersomepartition(inintellectu)ofBintolargish,visible parts(nonoverlapping);thefollowingpartition,letussay:Myleftandright legs (LL and RL), my left and right arms (LA and RA), my lower torso (LT), my upper torso (UT), my neck (N), my head, exclusive of my neck andmycerebrum(H),andmyleftandrightcerebralhemispheres(LBand RB). (The reader is advised at this point to make a visual aid: a “ginger- breadman”outlineofahumanfigurewiththelabels‘LL’etc.attachedto the appropriate sections of the figure.) Our imaginary adventure consists in the sequential replacement (in the order mentioned) of each of these parts of B by perfect duplicates (which had been grown in a vat or some- thing like that). Plantinga (speaking of his own case), imagines that this sequentialreplacementoccurswhileheisreadingtheSouthBendTribune. (As a staunch Kathleen Wilkes–style advocate of realism in philosophical examples, I am compelled, in adapting Plantinga’s argument to my own case,tosubstitutetheChicagoTribunefortheSouthBendTribune–foronly inverydistantpossibleworldsdoIeveropentheSouthBendTribune.)The sequence of replacements is integrated with the dormant/active cycle of my cerebral hemispheres in this manner: The sequence of replacements begins just before midnight; whichever of my cerebral hemispheres was dormant before midnight is replaced with a duplicate and is then annihi- lated;midnightcomes,andthe“relevantinformation”tokenedintheactive hemisphereiscopiedtothe(newlyinstalled)dormanthemisphere,which is then activated; simultaneously with its activation, the hemisphere that hadbeenactiveisrendereddormant;itisthenreplacedwitha(dormant) duplicateandannihilated. Now, following Plantinga’s example, I am to consider this imaginary episodeandIamaskedtoreasonasfollows: If this process occurs rapidly – during a period of one microsecond, say–Bwillnolongerexist.I,however,willcontinuetoexist,havingbeen readingthecomicpageduringtheentireprocess. The story is rather complicated. Let us set it out in the form of a time line. I shall suppose, as Plantinga has invited me to suppose, that thesequenceofreplacementstakesexactlyonemicrosecond.Letitbegin P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 194 PetervanInwagen justbeforemidnight,attheinstantt.Att,RBisdormantandLBisactive. Thenumbersrepresentnanoseconds(thousandthsofamicrosecond). t LLisreplacedandannihilated t 100 RLisreplacedandannihilated + t 200 LTisreplacedandannihilated + t 300 RAisreplacedandannihilated + t 400 LAisreplacedandannihilated + t 500 UTisreplacedandannihilated + t 600 Nisreplacedandannihilated + t 700 Hisreplacedandannihilated + t 800 RB(dormant)isreplacedwithaduplicate(RB*),also + dormant,andannihilated t 800 t 900 TheinformationinLB(active)iscopiedtoRB* + − + (dormant) t 900 RB*isactivatedandLBrendereddormant + t 1000 LBisreplacedwitha(dormant)duplicateand + annihilated. The one-microsecond interval t t 1000 is (we suppose) a subinterval − + of a twelve-second interval during which I read (and, in the words of The BookofCommonPrayer,inwardlydigest)thatday’s“Doonesbury”strip:At the start of the longer interval, I glance at the first panel; at the end of it,havingreachedthefourthandfinalpanel,gotthepoint,andchuckled, I have formed the intention to go on to “The Boondocks.” This whole twelve-second mental episode proceeds without interruption. When the one-microsecondsequenceofreplacementsoccurs,Idon’tnoticeathing: It has “no phenomenological consequences whatever.” It is evident that I existthroughoutthetwelve-secondinterval(“I,however,willcontinueto exist,havingbeenreadingthecomicpageduringtheentireprocess”)and that B does not – for the one-microsecond sequence of replacements has destroyedB. Thisstoryisevidentlymetaphysicallypossible,anditsmetaphysicalpos- sibilityestablishesthatitismetaphysicallypossibleforboththefollowing twopropositionstobetrue. Iexistthroughoutacertaininterval. Bceasestoexistatsomepointinthatinterval. And,aswehaveseen,thismetaphysicalpossibilitylogicallyimpliesthatI amnotidenticalwithB.(Hereendeththestatementoftheargument.) P1:JyD 0521855314c08 CUNY806B/Baker 0521855310 April17,2007 17:21 Plantinga’sReplacementArgument 195 3 Butwhy,onemightask,amItosupposethatthesequenceofreplacements destroys B? Well, I am willing to grant that it does. B is a living human organism, and a certain “minimum assimilation time” is required for an object to become a part of an organism – and this minimum assimilation timeiscertainlygreaterthanonemicrosecond(and,afortiori,greaterthan 100nanoseconds,theintervalbetweenthesuccessivereplacementsinthe story).Consider,forexample,aneyetransplant.Supposethatxisadetached but viable human eye.15 Suppose that x is not a part of Alice and then becomes a part of Alice. How long does it take for x to become a part of Alice?Howquicklycanthishappen?Well,itcertainlycan’thappeninstan- taneously.Therecannotbetwo“adjacent”intervals(twointervalssuchthat acertainmathematicalinstanttistheleastupperboundofonethemand thegreatestlowerboundoftheother)suchthatxisnotapartofAliceat anyinstantthatbelongstotheearlierintervalandisapartofAliceatevery instantthatbelongstothelaterone.Assimilation,whateverelseitmaybe, isacausalprocess,andcausalprocessestaketime.16Thismuchcanbesaida priori.Andweknowenoughaposterioritosaymore.Iftisthefirstinstant atwhichxis“spatiallyinplace,”isatthatplaceinAlice’seyesocketatwhich thesurgeonwantsittobe(supposing,unrealistically,thatbeinginplaceis a condition that can be achieved instantaneously), there will be an inter- valfollowingtduringwhichxisnotapartofAlice,andweknowenough aboutrateatwhichchemicalreactionsoccurtoknowthatthisintervalwill begreaterthanonemicrosecond(muchless,sotospeak,100nanoseconds). Butweneednotappealtoanyempiricalfacts(whichdohaveawayofturn- ingintoempiricalnonfacts).Theaprioripointissufficientforourpurposes: Iftheintervalsonemicrosecondand100nanosecondsshouldturnouttobe “toolong,”wecansimplyadjusttheintervalsbetweenreplacementsinthe example. Now consider any partition (again, in intellectu) of an organism into n nonoverlappingpartsP ,P ,...,P .IfthePsarereplacedsequentiallyby 1 2 n duplicates,andiftheintervalbetweensuccessivereplacementsislessthan the minimum assimilation time (or, even better, if the whole sequence of replacementstakesplaceinanintervallessthantheminimumassimilation time),theorganismwilltherebybedestroyed.17Nodoubtthe“replacement Ps”willprettyquicklycometocomposeanorganism–aduplicateofthe originalorganism–butitwillnotbetheoriginalorganism. I have conceded that the sequence of replacements, if it is sufficiently rapid,willdestroyBbecausethatthesisisaconsequenceofthemetaphysic