Imaginary Science

The British Society for the Philosophy of Science

Review: Imaginary Science Author(s): David Gooding Reviewed work(s): Thought Experiments by Roy A. Sorensen Thought Experiments in Science and Philosophy by T. Horowitz ; G. J. Massey The Laboratory of the Mind: Thought Experiments in the Natural Sciences by James Robert Brown Source: The British Journal for the Philosophy of Science, Vol. 45, No. 4 (Dec., 1994), pp. 1029 -1045 Published by: Oxford University Press on behalf of The British Society for the Philosophy of Science Stable URL: http://www.jstor.org/stable/687620 Accessed: 18/01/2009 09:49 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=oup. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with the scholarly community to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources. For more information about JSTOR, please contact [email protected].

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Brit.J. Phil. Sci. 45 (1994), 1029-1045

REVIEWARTICLE Imaginary

Sciencel

David Gooding 1 Theparadoxof a prioriempiricalimport 2 All in themind?

3 4 S 6 7

Touched-up beliefs Canan argumentbe an experiment? Thought-experimental methodsinphilosophyandin science Have thoughtexperimentsevolved? Experienceandintuitionin experiment

1 The paradox of a priori empirical import Thought experimentationis the most powerfulform of argumentation known to modern science. Thought experiments(hereafterTEs) are transparent,persuasive,and are accessiblein a way that few real experiments(hereafterREs) are. This shouldensurethema prominentposition in philosophyof science.However,most philosophersfind TEs mysterious. How can we know the outcome of an experimentwithout actually performingit? If it is sufficientto performan experimentin thought,why bother with real experiments?In The Laboratoryof the Mind, James Brown arguesthat some TEs appeal to intuition ratherthan empirical informationand neverthelessdelivera priori truths about reality. Such TEs vindicaterationalism.The choice that Brown offers us is between mysteryandPlatonistintuitions.His argumentmakesperplexityaboutthe powerof TEs a rhetoricalfulcrumon whichto levergood old-fashioned Platonisminto the position claimed by empiricists.His explanationis opposedby John Norton who arguesin his chapterin the volumeedited by Tamara Horowitz and Gerald Massey (hereafter,H&M), that in physics all TEs are deductiveargumentshaving empiricalpremises:the missing empiricalinput was there all the time, hidden in suppressed Oxford and New York, Oxford Review of Roy A. Sorensen [1992],ThoughtExperiments, University Press, pp. xxii+318; T. Horowitz and G. J. Massey (eds) [1991], Thought Experimentsin Science and Philosophy,Savage, M. D., Rowman & Littlefield, pp. of theMind.ThoughtExperiments ix + 355; James Robert Brown [1991], TheLaboratory in theNaturalSciences,London and New York, Routledge, pp. xi + 175.

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premises.In theirintroduction,Horowitzand Masseydescribeas the fact that TEs have 'novel empiricalimporteven though they are conducted entirelyinsideoneshead . . .' as the 'paradoxof thoughtexperiment'which they attributeto an early paper by Kuhn (H&M, p. 1). Severalof the contributorsto this collectionexplicitlyaddressthe paradoxin this form.2 Anotherexplanationof the informativenessof a TE appealsto the 'ways that old informationcan be renderedmoreinformative',as Roy Sorensen puts it in ThoughtExperiments (p. 4). Sorensendefendsa broadlyempiricist view but he deniesthe very existenceof the rationalist'sfulcrum.He attributeswondermentabout the informativenessof a priori armchair activityto the vaguenessof the usual accountsof how non-observational enlightenmentcan take place. These explain TEs as simply exploring hidden implicationsof what is alreadyknown but forgotten, as Plato argued,or as retrievingand applyingintuitionsformedfrom experience, as Machargued,or as exploringnewpatternsin existingdatastructures,as cognitivescientistsargue.In so far as one acceptsthe presuppositionson which the paradoxis bound to arise, I supposethere is little to choose betweenintuitionsthat are empiricallygroundedand intuitionsthat are mystically intuited. Reliance on Machian, empirical intuitions is an empiricistversionof Plato'sdoctrineof recollection. The air of paradoxis due partly to the rise of modernexperimental scienceand partly to some presuppositionsof analyticalphilosophy.In Aristotelianand medievalsciencethe narrationof an experimentoften supplantedactualperformance.As PeterKing shows in his essay on the meta-methodof medievalscience,the abilityto arguewith examplesand counterexampleswas more importantthan the productionof empirical evidence(H&M, pp. 47ff.). By the end of the seventeenthcenturythe privilegedstatusof scientia hadbeenchallenged:it wasno longersufficient to follow a processof reasoningabout the experiencesone wouldhave in somepossibleworld.Scienceceasedto be a purelytextualenterprise;ars, appliedin actualperformance,wasnecessaryto establisha fact.Narratives wereconstructedin such a way that readerscould witnessexperimental procedures.Experimentalnarrativesquicklybecamea meansof disseminatingresults,but from the seventeenthcenturyuntil well into the nineteenth,disseminationdependedon placingresultsin the context of the methodsthat producedthem. The new narrativesof Galileo, Boyle, and Newtonforceda distinctionbetweenthe narrationof possibleexperience andthe outcomesof real-worldobservationand experiment,makingan 2

Kuhn [1962], reprinted in Kuhn [1977]. This essay influenced many historians of science; for an application of Kuhn's analysis to the dynamics of real experiment see Gooding [1982, 1985], and [1990], Chs. 8-9.

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importantdeparturefrom the passive,Aristoteliannotion of experiment prevalentbeforethe scientificrevolution.3 The modern distinction between real-worldexperienceand mental simulationsof experiencemarksan importantdifferencebetweenphilosophyandsciencethatanalyticalphilosopherstendto gloss over.Sincethe seventeenthcenturyand especiallyin the twentiethcentury,philosophers separated the activity of experimentationfrom its results, reducing experimentto an unproblematicsource of the observationstatements that confirm or falsify theories. Reduced to the productionof observations, discovery was dismissed as irrelevantto the justification of theoreticalclaims about nature. Nevertheless,the processesof making things observable,countable, and measurable so as to make them manipulable by argument has epistemological significance. This becomesevidentas soon as we ask how scientistsestablishthe truth of the observationstatements.In consideringonly observationstatements, philosophersignored an important issue. Without an analysis of the experimentalpracticesinvolved in making observations,the epistemic force of real experimentshas remainedjust as mysteriousas that of TEs. Philosophershaveleft studyof the validationof observationstatements to historiansand sociologists.Theiranswersshow that observationsare nothinglike the unproblematiclinguisticentitiesthat most philosophers expect them to be.4 Except, that is, in a thoughtexperiment.In a TE, making an observationis never problematic.It is true that TEs offer control over all unrulyvariablesby stipulation(Sorensen,p. 205), but what TEs assume about the experimenteris also important:thought experimentersare made perfectlycompetent in their ability to follow proceduresand as perceiversof events and outcomes.This is not to say that the possibilityof makingsome observationis neverchallenged to deny observabilityis an importantstrategyin some TEs rather, the perceptualand experimental veridicalityof the thought-experimenter's competenciesis placedbeyond question.The truth of observationstatementsis givenin a TE.s A solution to the paradoxcan now be stated. The new experimental narrativesof the scientificrevolutionmadereal-worldpracticesimportant; real-worlddiscovery was necessaryto justification.But in a thought experimentthe contexts of construction,discovery,and justificationare legitimatelytreatedas one and the samething.TEs are self-containedin a way thatargumentscan be but no realexperimentcan everbe. Thereinlies 3 4 5

See Tiles [1993] for this distinction. See, for example, Pinch [1985] and Pickering [1989]. This argument is developed in Gooding [1993].

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theirpowerand theirappealto a philosophyin whichexperiencereduces to observationstatements.But thereis no mystery.

2 AUin the mind? Of the authors reviewedhere, Brown finds TEs most mysterious.The argumentof TheLaboratoryof the Mind(restatedin his essay in H&M andin Brown[1993])is thatTEspose a challengeto an empiricisttheoryof knowledgebecauseempiricistexplanationsof the TE'snovelimplications are denied. So we had better accept a rationalistexplanation.Brown developsa useful classificationof TEs as destructive(these are basically 'picturesque'reductioad absurdumarguments)or constructive.Constructive TEs can be mediativearguments(whichhelp derivea consequence from a theory), conjectural(which prompt an explanation for some imaginedphenomenon),or direct (leadingfrom an unproblematicphenomenonto a new theory).The most importantTEs are those whichare both destructiveand direct,makinga potentiallyfatal objectionto one theorywhile establishinggroundsfor believinganother.He labels these relativelyrareTEs 'Platonic'.Accordingto Brown,PlatonicTEs involve directintuitionof laws of nature,which he construesrealisticallyin the traditionof Armstrong,Dretske,and others. Brownmoves quicklyfrom physicalscienceto mathematics,wherehe arguesthe case for mathematicalrealism,before developinga Platonist accountof thoughtexperiments.He placesgreatweighton theexplanatory power of rational intuition because he needs 'somethingfor thought experimentersto see' with the mind'seye (p. 86). His expositionof nonverbalmodes of argumentationis welcome,but he offersno evidencefor intuitionapartfromthe appearanceof mysterythat it is meantto explain. Nor does he addressthe evengreatermysteryof how intuitionscometo be articulatedas statementsor picturesaboutreality.An obviousresponseis to offer alternativeexplanationsof the mystery,as Sorensenand some contributorsto Horowitzand Masseydo. Sinceso many associateKuhn with the paradoxof TEs, it is worthnotingthat in none of thesebooks do we find an accountin keepingwith Kuhn'srejectionof the rationalistempiricistdichotomy. A naturalisticaccount would incorporateboth empiricistand rationalistinterpretationsof how we come to perceive realityas somethingdistinctfrom our representationsof reality.Sorensen's analysis of experimentin terms of a continuum(with TEs as a limitingcaseof experiments)is an importantsteptowardssuchan account. I have arguedelsewherethat any descriptionthat arguesparadoxby denyingempiricalinput (as Browndoes) while assertingthat the performanceof a TE is a purelymentalaffair(as all the authorsreviewedhere

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seem to do) betraysa seriousmisunderstandingof what makes thought experimentationpossible and what makes it compelling.6If TEs were purelymentalaffairsthen they could not be performedat all, but if they are not purely mental affairsthen there is no paradox. An analogous mistakeis made by those who argue that expertiseand intelligencecan be expressedentirelyas computableprocesses.Ourmindsmay be able to simulatelaboratoryworlds, but they simulate only that which can be mentallyrepresented,so they necessarilyomit much that real experiment involvesand most of what makes thought experimentpossible,namely, real-worldknowledge.Neglect of this point explainswhy Norton findsit 'remarkable'that one of Einstein'sTEs on black body radiationcan be analysedentirelyqualitativelywithoutloss of rigour(H&M,p. 133).This is whatwe shouldexpect.A TE achievesargumentativestatusby eliminating procedures,concepts,and what Sorensencalls the 'apparatusesthat bridge abstractionto particulars'(p. 208). Introduce the complexity needed to support rigour (e.g. logical and computationalprocedures, associated classificationsand quantification,methods of calibration, etc.) and the narrativebecomes too complicatedto work as an argument. The contrastbetweenthe transparencyof textbookdescriptionsof crucial (real) experimentsand the opaquenessof detailed instructions neededto replicatesuchexpenmentsshows this. A TE expressesthe minimumset of conditionsnecessaryto sustainthe appearanceof an argument,generalizingit whilstgivingthe appearanceof the situated-nessthat realexperimentsactuallyhave. As RonaldLaymon points out in 'Thought Experiments. . . as Ideal Limits', how far the simplificationcan proceeddependsupon how muchthe audiencealready knowsaboutthefieldof argument,thatis, howmuchthey'canbe expected to imaginefor themselvesthe sortsof experimentalrefinements'proposed and to believe 'on the basis of their experiencewith . . . analogous experiments'that such refinementsare possible (H&M, pp. 171-2). The experienceof experiments,the elementof personalparticipation,is what makesa TE more than an argument.That is why it is naturalto speakof 'performing'a TE yet seemsodd to say that we 'perform'an argument.7

3 Touched-upbeliefs In his thought-provokingbook, Roy Sorensenadvancesa generaltheory of TEswitha viewto understandingtheirimportanceto philosophyas well 6 7

Gooding[1990],Ch. 8, and [1992]. Ian Hackingalso argues that it is the 'bodily feel' conjuredup by the languageof experimentthat convinces(Hacking,[1993],p. 305). Our understandingof languageis often groundedin our own experienceas embodiedagents(see Johnson[1987]).

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as to science. Sorensenmoves beyond Mach's explanationof TEs as exposingunarticulatedexperiencesto developa view of TEs as evolving fromREs by a processof attenuation,abstraction,and simplification.He arguesthat there is a symmetricalrelationshipbetweenthought experimentsandrealones.Sincethe formerarea limitingcaseof the latter,study of eithersortof experimentshouldhelpus understandthe other.His main objective, however, is to understandphilosophicalTEs through their resemblanceto REs. Sorensenoffersa new modelof TEswhichhe callsthe 'cleansingmodel of armchairinquiry'.This worksby eliminatingintellectualvices such as inconsistency,bias, and circularity.Had he paid more attentionto the workingsof REs,he couldhavepointedout thatthisis also howreal-world experimentproceeds,throughthe refinementsand reformsdemandedby the process of criticismby other scientistsand-through the complex interplay of success and failure in experiment by nature. A similar point is made by John Forge in his essay on TEs in physical science (H&M,pp.212ff.). Sorensenwantsto developthe insightof Kuhn's'Functionfor Thought Experiments'that TEs disclosea local sort of contradictionwhiledefending logic againstthe Kuhnianheresythat standardlogic has no placefor thenotionof a local,contingentformof contradiction.He restoresthe role of standardlogicby analysingthe paradoxicalcharacterof TEsin termsof a theoryof conflictvagueness(pp. 167ff.).TEsinvolverefinementthrough precisificationof concepts. But there is a price. It turns out that what standardlogic can be applied to is not science as practised(in which paradoxlurkseverywhereand is constrainedby local conceptualreform, criticism,and by the reconstructionof experimentsas arguments)but the idealized,textualworldof the experimentalnarrative. The need to reshapeTEs to fit theminto a taxonomybasedon a single schemais a furtheridealizationof the alreadyartificial.Sorensenacknowledges that this may 'strikeus as unnaturaland even perverse';nevertheless,it is justifiedbecauseit preservesthe 'logicalmerit'of a 'global' characterizationof TEs (pp. 165-6). Have we tradedthe narrativesof Boyle and Newton for those of Aristoteliansand scholastics?The 'disfigurement'is morethanaestheticand rhetorical.By drawingus backinto the realmof imaginaryscienceit compromisesthe relevanceof Sorensen's analysis to philosophy of science. Reconstructionmakes for a selfcontained argument,but a self-containedargumentis no experiment. Argumentswhichcannotintroducenew information,executedby disembodied reasoners,do not (as Hackingputs it) have a life of their own.8 8 Hacking [1993], p. 307.

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Betterto constrainthe applicabilityof standardlogic, as Kuhn'shistorically informedaccount does, than to reconstructalready 'touched up beliefs'that bearless resemblanceto the subjectmatter.

4 Can an argumentbe an experiment? Many contributorsto Horowitzand Massey'svolumemaintainthat TEs arejust arguments,thoughthey differabout the degreeto whichthey can be reduced to a particularform. Although Brown and Norton take opposite views about the importanceof visualizationto argumentand about the source of the 'new' informationdisclosed through thought experimentation,they sharetwo assumptions:that no new information is introducedduringthe performanceof a TE, and that the (logically) reconstitutedargumentis theproperobjectof analysis.Norton arguesthat TEs in physics are a form of deductiveargumentinvolving empirical premises.This kind of TE is a graphical,narrativeexposition of tacit empiricalpremisesthat works by drawingattentionto (unnoticed)consequencesof the premises.A TE is an enthymeticversionof a deductive argumentwhichpositshypotheticalor counterfactualstatesof affairs,and which invokes particularsirrelevantto the generalityof the conclusion (H&M,p. 129).Theparticularsareempiricalstatesof affairs.On Norton's analysis the differencebetween a TE in its unreformedstate and a reconstructedTE is no greaterthan the differencebetweena high-level algorithmthat calls many other functions and the computationof the algorithm,which requiresthat all constituent(nested)functionsbe suppliedwith parameters(suchas particularvaluesproducedby observation, measurement,etc.) so that they can be evaluated. Norton's reductivemethod exposes the empiricalinformationthat, accordingto Brown'saccount, must otherwisebe intuited.However,it raisesotherquestions.EvengrantingthatanyTE can be reconstructedas a deductiveargumentwith empiricalpremises,it does not follow that TEs arejust deductivearguments,nor does this explainhow they work. If the object of reconstructionis to recast narrativesinto a logical form then exposingsuppressedpremiseswouldbe all thatis at issue.Butthe logicof a rationallyreconstructedTE alwayscomesfromthe formof argumentit is made to fit. Surely the logical form of an argumentcan be open to investigation?Otherwisethis methodcannot tell us whetheran empirical premiseflushedout by the analysiswas 'always'there or whetherit has been introducedbecauseconsiderationsof completeness,validityor epistemologyrequireit. The rangeof TEsconsideredby the twenty-oneessaysin H&Msuggests a broaderdefinitionthat includes,for example,mental anthropological

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fieldworkand illustrative,Panglossianstories.In 'Do All RationalFolks ReasonAs We Do?'BarbaraMasseyconsidersthoughtexperimentsabout tribes whose reasoninginvokes differentlogics that imply differentbut non-arbitrarylaws of thought(H&M,p. 101).She reconductsFrege'sTE aboutbeingswhoselawsof thoughtcontradictours,to showthatwe 'need not locatean actualtribeexhibitingconversationalpeculiarities',provided thatourTE presents'thesortof datawhichwouldlendconvincingsupport to a diagnosisof logicaldeviance'(p. 103).A TE is a well-toldstorywhose plausibilitydependslargelyuponits beingsufficientlydetailedto makethe unrealconceivable.In 'DarwinianThoughtExperiments'JamesLennox arguesthe case for 'justso stories'told by Darwin,Jenkins,and Dawkins. Theseillustratethe explanatorypowerof a theorywithoutclaimingto be truein detail,sincethe detailsarenot known(pp. 238-41). AndrewIrvine arguesthat the distinctionbetweenhypotheticalreasoningin generaland TEs in particularrequiresrecognitionof featuresof TEs that otherforms of counterfactualreasoningdo not share,and whichat leastsome REs do share:theymusttakeplacein the contextof an explicitlyscientificmethod (H&M, pp. 158-9). This rules out scientificstatus for the TEs of the Presocratics(H&M,p. 159) and possiblyMassey'smentalanthropology as well. The reductionof TEs to argumentsis 'popularamong philosophers becausethey areargumentexpertsand the shortestpathto understanding is to explain what you do not know in terms of what you do know' (Sorensen,p. 214). But with sufficientingenuityone can makeeithersort of experimentlook like an argument(p. 214). However,since 'interpretativeintrusion'is inevitable,Sorensenrecommendsthatwe grinand bear it; afterall, 'thedistortedvisionis usuallyof higherlogicalqualitythanthe raw original'(p. 133). His notion of TEs is much broaderthan that of Brown,Norton, or Forge we need to ask whetheran argumentis even intended:'The trouble scholarshave had in formulatingWittgenstein's privatelanguageargumentsuggeststhat Wittgensteinmay not have had any exactargumentin mind.Thoughtexperimentscan be equallyelusive (p. 134). Sorensenapproachesreconstructionas a way of classifyingTEs. His analysisof TEs as excursionsto possibleworldsdrawsattentionto how 'eachpartof a thoughtexperimentis organisedtowardthe ultimateend of modal refutation' that is, of controvertingan assertionabout something's being permissible,impermissible,known, believed, possible, or necessary(p. 33). The classificationis based on the types of flaws that TEs are intendedto expose. Since these involve some form of inconsistency,the taxonomydoublesas a theoryof fallacy.Any TE shouldconsist of a set of five sortsof statementwhich,sincethey arejointlyinconsistent,

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invite reformthroughrevisionor abandonmentof one of their number. Sorensen'sschemeincorporatesa greatmany examples,though he does not claim that all forms of argumentationconfirmreadilyto the three modalities (deontic, epistemic, alethic) on which his scheme is based. Authors of TEs are just as ingeniousin respondingto objectionsas the perpetratorsof realexperimentsare. It is alwayspossibleto modifya TE, so is the newset of propositionsa newexperiment?Sorensenrightlyasserts that flexibilityand disregardfor logical impossibilityare an important feature,makingTEs 'as tough as subwayrats'(p. 161). Naturalistic explanationsrequire us to prise TE apart, separating constructionand discoveryfrom justification,in order to explain their efficacyby lookingat how performingthemreconstructsour beliefs.None of the authorsof the worksunderreviewwouldacceptthe needto do this: self-sufficientnarrativesincorporatingreconstructedargumentsare the only kind that matter.The reconstructedargumentis equivalentto whatevermadeit possiblein the firstplace.ButconsiderNewton'sargumentin TheSystemof the Worldthat as the starting-pointof the trajectoryof a projectilebecomeshigherand higherit will eventuallygo into orbit.9This can be seen either as a form of incrementalargumentor as a piece of deductivereasoning.As an incrementalargumentit exploresthe consequencesof a systematicchangein some parameter,leadinggraduallyto a conclusionthat would be counterintuitiveif the final state of affairswere presentedfirst. As a deductiveargumentit presentsdirectlythe consequence of applying the laws of gravitationaland centripetalforce to projectiles. Whateverthecasefor reducingTEsto the formof arguments,it doesnot follow that they aremerelyarguments.As narratives,TEs arelinguisticas performin well as pictorial, yet the operationsthought-experimenters constructingthem are not necessarilyon linguisticrepresentationsbut upon a mentalmodel whose elementsand structuremay be represented My studiesof the way that TEs emergefrom the fine non-linguistically.l? structureof real experimentsshow that they articulate discrepancies betweenpracticalunderstanding(proceduralknowledge)and linguistic representationsand the importanceof the interactionof differenttypes of perception (and hence, of embodiment)to their constructionand performance. Richard Rorty once remarkedof the exemplarypuzzle-solvingthat Kuhn callednormalscience,that it is as close as real scienceever gets to the epistemologist'snotion of rationality.llIt would be a great shameif 9 Newton 11729],pp. 550-5. 0 Nersessian [1993], p. 294 Rorty [1980], p. 320.

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scientists'thoughtexperimentswereonly as close as philosophers'notion of empiricalargumentevergets to real science.

5 Thought-experimental methodsin philosophyandin science Thoughtexperimentmakes observationeasy, leavingus free to concentrate on assumptionsand argumentsratherthan interpretation,instruments, and practicalcompetence That is why scientistsfind them so useful, and why philosophersprefer them. Sorensen regards TEs in scienceand philosophyas differingin degreeratherthan kind. Horowitz and Masseyand theircontributorsemphasizesimilaritiesbetweenthe use of TEs in science and argumentby counterexampleas a philosophical method. They go further,however,to argueagainstthe demarcationof philosophy from science. Their introductionopens with an argument against the idea that making observationsis what differentiatesscience fromphilosophy.The argumentgoes like this: 1. Observationmay be passiveor active. 2. Experimentationis planned,activeobservation. 3. Scientificexperimentsareat leastas likelyto be thoughtexperiments as real ones, and 4. Philosophersconductthoughtexperiments,therefore 5. Observationdoes not provide a clear demarcationline between scienceand philosophy. Therearetwo seriousflawsin this argument.The thirdpremisehintsat an empiricalbasis for the claim of equal likelihood.To sustainit we would haveto examineactualhistoriesto determinethe relativefrequenciesof realand thought experimentsin science.TEs are found in the deepest recessesof real experimentation,about mattersrarelyimaginedin philosophers'mental laboratories.In so far as philosopherscan successfully conductTEs, this is because they share and participatein the same discursive practicesas the authorsof those TEs. Scientistsare well aware thatreal experimentexposes mattersthat thought does not anticipate. Horowitzand Massey call premise 3 a 'reflection':it looks more like wishfulthinkingto me. It is plausibleonly if we firstreducescienceto its coretheories and then reduce theorising to what finds its way into narratives, equations,and arguments. My second objection invokes the distinctiondrawn earlier between passiveand active observation.This is preciselywhat doesdemarcate philosophyfrom science. However actively philosophersmanipulate linguistically representedobjects, their observationis always passive withregard to the world, whereas that of scientistsis nearly always

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active.The more scienceis identifiedwith the ready-represented worldof discourse(as of courseit is in TEs),theharderit is to sustainthedistinction between observationas active interventionand the passive, simulated observationin narratives.H&M's argumentpurportsto be empirical, but it projectson to sciencean imagethata particularstyleof philosophizing requiresthat science have. The philosophy is real enough but the scienceit portraysis imaginary.

6 Have thoughtexperimentsevolved? Sorensenarguesthat TEs evolvedfrom REs by a processof 'attenuation'. This could mean either that it is possible to describea continuumof increasingabstraction,simplicity,and transparencyon which TEs are 'limitingcases of [real]experimentjust as circles are limiting cases of ellipses'(p. 186), or that there is an explanationwhich shows the continuumto be a consequenceof some evolutionaryprocess.If there is a continuumfrom thought to real experiments,it should be possible to describethemin termsof it. Sorensen'sargumentproceedsby supposition ratherthanexample:suppose thatTEs areItEs slimmeddownby a process of simplificationto just the instructionsand procedures,then we would have experimentsthat are 'all talk and no action'but in whichthe useful functionof proceduresis retainedindependentlyof actualexecution(pp. 190-1). Theexperimentalenterpriseis a hybridof thought-andreal-world executions.As experimentersnote the epistemicbenefitsof un-executed proceduresthey put these in place of real ones. Now suppose that a thoughtexperimentis simplyan experimentin which all real procedures have been replacedby designs. Thisis fantasy.Experimentsaremorethancarefullylaidplans:muchof what scientistsknow about the world is learnedby conductingexperiments,not by planningthem.Discursivepracticesrepresenta greatdealof experientialknowledge.Mach'saccountimpliesthat as the subjectmatter becomesmore familiarso TEs should becomemore powerfuland more accurateas guidesto conceptualreform.l2But Sorensenoverlookswhat makes the differencehere, namely the representationaladequacyof the scheme of concepts in terms of which procedurescan be represented, communicated,and executed in thought. As representationalpower improves, so it becomes easier to communicatethe essentials of an experimentto others.The capacityfor thoughtexperimentationabout a domainwould developas the representationalcapabilityof the language of that domainincreases.However,that capabilityis developedthrough 12

See Mach [1905].

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real-worldexperimentswhich enable scientiststo make informedjudgementsaboutthoseaspectsof theexperimenter's worldthatcanbe idealized withoutthe loss of relevantinformation. In his brief discussionof the role of empiricallessons learnedin the conductof realexperiments,Sorensenhintsat an explanatorythesiswhen he points out that '[t]houghtexperimentsare equallydependenton their trackrecords'(p. 195).Buthis supposedcontinuumof increasedsimplicity is only meantto show that executiondoes not supporta differentiationof thought-fromrealexperiments;it amountsto no morethan the assertion of (possible)evolution.It does not explainthe transitionfromone typeto the otherbecauseit does not addressthe historicalandcognitiveprocesses requiredby a naturalisticexplanation.Thiswouldhaveto be arguedboth as a historicalthesis(showinghow the extentto whichTEs are used in a field is indicativeof the representationalpower of the languageof that field)andas a cognitivethesis(showinghow TEsarticulatetheessentialsof what has been learnedthroughthe conduct of many real experiments). Since both types of experimentrequirethe masteryof a range of skills (logicalskills, skillsin the applicationof rules,etc.), what links TEs and REs is the developmentand disseminationof such skills.

7 Experienceandintuitionin experiment All argumentrequiresidealizationbut the risks are more serious for philosophythan for science.An idealizationpresupposesmany counterfactualassumptions.In sciencethose that matterare exposed,sooner or later.In philosophy,however,constraintsarefewer.Sorensen'sdiscussion (pp. 50ff.) of Mach'sattemptat a naturalisticexplanationof TEs is a case in point. He notes that Mach's explanationimplies the non-egalitarian notion of a hierarchyof thinkershaving differentabilitiesdue to their differentdegrees of experienceof the world. This is implied by any explanationthat appeals to the benefit of sensoryexperience,whether that has been assimilatedin the very briefspan of cognitiveprocessesor through the slow processes of natural selection. Those 'with greater experiencetend to have more accurate thought experimentsbecause theirveteranminds have been broughtinto finertune with the environment'(p. 59), or, as Mach would say, they have betterintuitions.I have two criticismsof this argument.First,accuracyis the wrongnotion here. (It is a creditto the wealthof examplesin Sorensen'sbook that I shalluse one of his otherexamplesagainsthim.) The firstexampleis an argument thatthe speedof lightcanexceedthemaximumsignalvelocityc: as a rodis extendedupwardsfromthe surfaceof the rotatingearth,so the velocityof its tip would eventuallyexceedthe speedof light (pp. 149-50). Physicists

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willrespondby introducingconsiderationsomittedfromthisTE-such as the originof the materialused to extendthe rod. Sorensenconcludesthat 'theappearanceof possibilityis a productof intellectuallaziness'(p. 150). Theproblemmightbe ignoranceof the relevantphysicsratherthanfailure to apply it consistently.An example of the problem of applicationis uncertaintyabout what happens to a very small hole bored througha large metal ring when the latter is heated:does the hole get larger or smaller?Besides knowing that heating causes expansion you need to know how to apply this fact (but even then there is room for doubt about the result). What is neededhere is a combinationof empiricalknowledgeand the abilityto reasonwith it. Thesearematterswhichthose of us not endowed with rationalintuitionmustlearn.I sidewith MachandWundt(p. 61) on the importanceof introspectiveexperimentbeinginformedanddisciplined by experience.Theefficacyof a TE tradesheavilyon how wellinformedits perpetratorsare about the worldwe are invitedto explore-whether the world is real or imaginary.Here, experienceincludesknowledgewhose transmissionhas been entrustedto social institutionssuch as our education system. Even Jim Browncould not intuit the natureof quantum andreasoning reality,hadhe not beeneducatedintomodesof representation verydifferentfrom those availableto the slave boy in Plato'sMeno. My second objectionconcernsthe analyticalstyle of philosophizing about science. It is ironic that Sorensenrepeatsa well-knownmyth in supportof an argumentabout the epistemologicaladvantagesof being informed.His argumentcalls for an exampleof a scientistwith an innate gift, for instance, Faraday's'instinctivegenius for physical experimentation'.The case for innatenessis that Faraday'workedhimselfup from the slums. . . withalmostno formaleducation. . . [yet]managedto conduct the best experimentalwork of his day' (pp. 59-60). Thus Sorensenspeculates that 'Faradayhad a lucky matchwith his universe'and goes on to argue in evolutionarystyle that differentcognitive capacitiescould be 'hard wired', conferringdifferentialadvantages on progeny, so that some would 'secure a running start in the mastery of nature'. These 'lucky winners will have an uncanny feel for the rhythms of nature'. From the existenceof such 'superfit'physicalexperimenterslike Faraday he then infers the existence of analogous cognitive predilectionsfor structureneeded for superfitTEs as well. Their fitness 'would be a matter of absolute cognitive power' (p. 60). So Galileo, Newton, and Einstein could owe 'some of their success with TEs to a lucky, tight match between genes and environment'.This is no more convincing than Brown'srationalistexplanationof tight matchesbetweenintuitions and reality.

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This particularargumentis uncharacteristically sloppy,and one of its majorpremisesis false. This fact pointsup the differencebetweenrationalist, empiricist,and naturalisticapproachesto TEs. Faradayhad a long apprenticeship to HumphryDavy andThomasBrande,two of the leading analyticalchemistsandexperimentalists of the time.Thistook placein one of Europe'sbest-resourcedresearchinstitutions.l3The period 1813-20 involved experienceand opportunitiescomparableto a postdoctoral fellowshipat one of today's top researchinstitutions.This fact does not diminishthe significanceof Faraday'sexperimentalgenius,whichinvolved a great deal of thought-experimentation about the implicationsof his materialmanipulations.Rather, it shows that Faraday's'fitness'need not be explainedentirelyby geneticallyendowedcapacities.Faraday's successowed much to sheerpersistenceand painstakingattentionto the detailsof experiment.In this respecthe is similarto Euler.MarkWilson's accountof Euler'sdisputewithd'Alembertaboutthepropermathematical descriptionof a plucked string illustrateshow 'the dogged pursuit of mathematicalrigoralone can lead one naturallyinto the most novel and unexpectedterrain'(H&M,p. 194).Brown'sreconstructionof Einsteinas a long-standingrationalistbetraysa similarlycavalierattitudeto fact; it contradicts(by assertion rather than evidence) historical studies that suggest Einstein moved from a Machian empiricism(which included severalimportantTEs) to a rational realism.l4Though Brown claims that historyof sciencesupportshis reconstructionthereis little evidence that historianswould recognizein his account. Surely it matters, even in analyticalphilosophy, whether assertions offeredas evidenceare in fact true?Sorensenmakes a methodological prescriptionthat TEs should be studiedas if they wereexperiments,not arguments,remarking:'[t]hesuccessfultheoreticalfictionis rare.Usually, thingsaremost successfullystudiedundertruedescriptions'(p. 215). Yet he neglects fact again in his challenge to Mach's assertion that '[e]xperimentation in thought is an indispensablepreconditionfor the executionof any physicalexperiment'.This claim stretchesthe notion of a TE to include any kind of forethoughtabout experiment(p. 74) a move also rejectedby Irvine,Laymon,and othercontributorsto H&M.A more direct objectionwould be to analyseexamplesof thought experimentsoccasionedby realones.His maximabouttruedescriptionscouldbe appliedby pointingout that Mach'sclaimis actually false:therearemany examples of physical experimentationin which TEs arise preciselyin 13

14

It included a tour of France, Switzerland, Italy, Germany and Belgium, during which Faraday met many leading scientists and assisted with Davy's experiments, including the discovery of iodine; see Bowers and Symons [1991] and James (ed.)[1991]. See Holton [1968].

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situationsthatwouldnot existapartfromthe experimentation andwherea conflictbetweenlanguageand practiceforces thoughtto experiment(as Kuhnputs it), to helpclarifyor articulatethe meaningof conceptsapplied in experiment.ls It would be difficultif not impossibleto discoverthis sort of function withoutlookingbeyondphilosophicaldiscourse.Thisshowsup an important differencebetweenphilosophizingthat seeksgeneralityof description through trial by counterexampleand science, which actively seeks to transcendthe frameworkof representation. The appearanceof threebooks about TEs so soon afterseveralstudies of real experimentsin sciencemightwell be greetedwith sighs of relief.l6 Surely philosophersneed not after all grapple with the complexities, contingencies,and often tediousdetailsof real experiment.Sorensenand Massey advanceargumentsagainst such complacency.Thereis no substitutefor studyingthe realthingeitherin scienceor in philosophy.l7For Sorensen,the studyof RE informsthat of TE (andvice versa),so the need to understandthe use of TEs in philosophyis inseparablefrom being informed about the use of any sort of experimentin science. Gerald Masseymakesa similarpoint in 'BackdoorAnalyticity',arguingthat in theiruse of TEs as counterexamples whichappealto conceivablestatesof affairs,philosophersshould avoid facile conceptionsand instead try to match the standardsof conceivabilitythat have been developedin the sciences(H&M,pp. 23, 291-2). Massey'sexampleof a facileconceptionis Hume'sattemptto refuteconceptempiricismby instancinga personwho can imaginean intermediateshadeof blueneverseenbefore.Humeclaims the counterexampleis 'so particularand singular'that it does not require him to alterhis thesis that all simpleideas are obtainedfrom experience. Althoughthe exceptionalmightbe ignoredwhenarticulatingsimplerules or streamliningfor pedagogicalefficiency,Sorensen criticizesHume's dismissalof this counterexamplebecauseHume was developinga philosophicalsystem, 'an enterprisein which practicalconsiderationsdo not justifydismissalof rarecounterexamples' (p. 134). RichardGale addressesintuitionsabout counterexamplesin 'On Some PerniciousThoughtExperiments'.Galeidentifiestwo typesof analytically perspicaciousTEs: clear-cutcounter-examplesand those which present cases that are undecidablebecausethe applicationof a concept(such as personalidentity)involvesseveraldistinctsetsof criteria(e.g.embodiment 15 16 7

Kuhn [1977], p. 258. Batens and van Bendegem (eds)[1988], Franklin [1986], Galison [1987], Gooding, Pinch, Schaffer (eds)[1989], LeGrand (ed.)[1990]. An extensive literature on experiment has developed since the pioneering work of Fleck, Duhem, Koyre, and Conant: see Holmes [1992].

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in this particularbody; having this set of memories,competencies,etc., H&M, p. 298). A languagegame is playableif undecidablecases do not occur frequentlyenough to underminethe rulesand if the conditionsin whichit is playeddo not defeatthepurposesof playing it. What'sat issueis whetherthe worldis one in whichthe languagegame analysedis possible or one in whichit wouldbe futileto engagein it. UndecidableTEsbecome perniciouswhen they fail to addressthe questionof how exceptionalthe imaginedcase is. Many sciencefictionTEs fall into the perniciouscategory. But what is the basisfor an intuitionthat a case is undecidableand thatan undecidablecaseis exceptionalratherthan facile?We arebackto a contestof intuitionsabout possibilities. The answer,surely,lies in Sorensen'sand Massey'sbelief that understandingthe scientificuse of thoughtexpenmentscan advanceour understandingof the method of argumentby counter-examplein philosophy. However,that understandingof science calls for a more systematic comparisonof real and thought experimentsthan Sorensenor anyone elsehas so far attempted.Withoutit, and not-with-standingthe abundanceof stimulatingexamplesin thesebooks, accountsof thoughtexperimentsas limitingcases of real ones lack substance. Science Studies Centre Universityof Bath Bath BA2 7A Y UK

References Batens, D. and van Bendegem,J. P. (eds) [1988]: Theory

and Experiment: Recent Insights and New Perspectives on their Relation, Dordrechtand Boston, D.

Reidel/KluwerAcademic. Bowers, B. and Symons,L. [1991]:CuriosityPerfectly Satisfyed: Faraday's Travels in Europe, 1813-1815, London,Peter Peregrinus. Brown, J. R. [1993]:'WhyEmpiricismWon'tWork',in Hull D., ForbesM., and OkruhlikK. (eds), [1993],pp. 271-79. Franklin, A. [1986]:The Neglect of Experiment,Cambridge, CambridgeUniversity Press. Galison, P. [1987]:How ExperimentsEnd, Chicago, ChicagoUniversityPress. Gooding, D. [1982]:'Empiricism in Practice:Teleology,EconomyandObservation in Faraday'sPhysics',Isis, 73, pp. 46-67. Gooding, D. [1985]:' "InNature'sSchool":Faradayas an Experimentalist', in D. GoodingandF. James(eds), Faraday Rediscovered: Essays on the Life & Workof MichaelFaraday, 1791-1867, London,Macmillan [1985],New York,American Instituteof Physics[1989],pp. 105-35. Gooding, D. [1990]:Experiment and the Making of Meaning: Human Agency in ScientificObservationand Experiment, Dordrecht, KluwerAcademic.

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Gooding, D. [1992]: 'The Cognitive Turn, or, Why do Thought Experiments work?' in R. Giere (ed.), CognitiveModelsof Science,Minneapolis, University of Minnesota Press, pp. 45-76. about Thought Experiments?',in Hull Gooding, D. [1993]: 'What is Experimental D., Forbes M., and Okruhlik K. (eds),[1993], pp. 280-90. Gooding, D., Pinch, T. and Schaffer, S. (eds) [1989]: The Uses of Experiment, Cambridge, Cambridge University Press. Hacking, I. [1993]: 'Do Thought Experiments have a Life of Their Own?' in Hull, D., Forbes M., and Okruhlik K. (eds),[1993], pp. 302-8. Holmes, L. [1992]: 'Do We Understand Historically How Experimental Knowledge is Acquired?' Historyof Science,XXX,pp. 119-36. Holton, G. [1968]: 'Mach, Einstein and the Search for Reality', Daedalus,97, pp. 636-73, reprinted in Holton, ThematicOriginsof ScientificThought,Keplerto Einstein,Cambridge, MA, Harvard University Press [1973], pp. 219-59. Hull, D., Forbes, M., and Okruhlik, K. (eds)[1993]:PSA 1992, VolumeTwo,East Lansing, MI, Philosophy of Science Association. James,

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