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The Problem of the External World môn Principle of Management | Trường Đại học Quốc tế, Đại học Quốc gia Thành phố Hồ Chí Minh

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Lan Anh Trần

19 giờ trước

Tải xuống Báo cáo

Danh sách Quiz

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UniversityPressScholarshipOnline

OxfordScholarshipOnline

TheSignificanceofPhilosophicalScepticism

BarryStroud

Printpublicationdate:1984

PrintISBN-13:9780198247616

PublishedtoOxfordScholarshipOnline:November2003

DOI:10.1093/0198247613.001.0001

TheProblemoftheExternalWorld

BarryStroud(ContributorWebpage)

DOI:10.1093/0198247613.003.0001

AbstractandKeywords

Chapter1setsouttheProblemoftheExternalWorldtowhichscepticismisanatural

response:theproblem,firstposedbyDescartesinhisFirstMeditation,ofhowtoshow

thatwehaveanyknowledgeabouttheworldaroundus.

Reflectingonthenatureofhissensoryexperiences,Descartesfindshimselfunableto

ruleoutthepossibilitythatheisdreamingand,onthataccount,driventothedevastating

conclusionthatheknowsnothingatallabouttheworldaroundhim.Stroudarguesthatif

Descartesisrighttoinsistthatinordertoknowsomethingabouttheworldaroundhim

hemustknowthatheisnotdreaming,thenheisalsorightthathehasnosuch

knowledge,becausetheconditionforknowledgethatDescartesacceptscanneverbe

fulfilled:fulfillingitwouldrequireknowledgewhichitselfwouldbepossibleonlyifthe

conditionwerefulfilled.

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Themorepromisingstrategyinthefaceofthescepticalargument,therefore,isto

examinemorecarefullytherequirementthatwemustknowthatwearenotdreamingif

wearetoknowanythingabouttheworldaroundus.

Butifthatrequirementisafactofourordinaryconceptionofknowledge,asitseemsto

be,wemustacceptit,becausethereisnonotionofknowledgeotherthantheordinary

onethatisembodiedintheproceduresandpracticesofeverydayandscientificlife;and

unlesswefindawayofrejectingtheproblemaltogether,wewillhavetoacceptwithitthe

conclusionthatnooneknowsanythingaboutworldaroundus.

Keywords: conditionsofknowledge,Descartes,dreaming,FirstMeditation,ordinaryconceptionof

knowledge,Possibilityofknowledge,ProblemoftheExternalWorld,rejectionoftheproblem,sc eptical

argument,sc epticalexperienc e

SinceatleastthetimeofDescartesintheseventeenthcenturytherehasbeena

philosophicalproblemaboutourknowledgeoftheworldaroundus.1Putmostsimply,

theproblemistoshowhowwecanhaveanyknowledgeoftheworldatall.Theconclusion

thatwecannot,thatnooneknowsanythingabouttheworldaroundus,iswhatIcall

‘scepticismabouttheexternalworld’,sowecouldalsosaythattheproblemistoshow

howorwhyscepticismabouttheexternalworldisnotcorrect.Myaimisnottosolvethe

problembuttounderstandit.Ibelievetheproblemhasnosolution;orratherthatthe

onlyanswertothequestionasitismeanttobeunderstoodisthatwecanknownothing

abouttheworldaroundus.Buthowisthequestionmeanttobeunderstood?Itcanbe

expressedinafewEnglishwordsfamiliartoallofus,butIhopetoshowthatan

understandingofthespecialphilosophicalcharacterofthequestion,andofthe

inevitabilityofanunsatisfactoryanswertoit,cannotbeguaranteedbyour

understandingofthosewordsalone.Toseehowtheproblemismeanttobeunderstood

wemustthereforeexaminewhatisperhapsbestdescribedasitssource—howthe

problemarisesandhowitacquiresthatspecialcharacterthatmakesanunsatisfactory

negativeanswerinevitable.Wemusttrytounderstandthephilosophicalproblemofour

knowledgeoftheexternalworld.

TheproblemaroseforDescartesinthecourseofreflectingoneverythingheknows.He

reachedapointinhislifeatwhichhetriedtositbackandreflectoneverythinghehad

everbeentaughtortold,everythinghehadlearnedordiscoveredorbelievedsincehe

wasoldenoughtoknowor(p.2) believeanything.2Wemightsaythathewasreflecting

onhisknowledge,butputtingitthatwaycouldsuggestthatwhathewasdirectinghis

attentiontowasindeedknowledge,andwhetheritwasknowledgeornotisprecisely

whathewantedtodetermine.‘AmongallthethingsIbelieveortaketobetrue,what

amountstoknowledgeandwhatdoesnot?’;thatisthequestionDescartesaskshimself.It

isobviouslyaverygeneralquestion,sinceitasksabouteverythinghebelievesortakes

tobetrue,butinotherrespectsitsoundsjustlikethesortofquestionweareperfectly

familiarwithineverydaylifeandoftenknowhowtoanswer.

Forexample,Ihavecometoacceptovertheyearsagreatmanythingsaboutthe

commoncold.Ihavealwaysbeentoldthatonecancatchcoldbygettingwetfeet,orfrom

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sittinginadraught,orfromnotdryingone'shairbeforegoingoutdoorsincoldweather.

Ihavealsolearnedthatthecommoncoldistheeffectofavirustransmittedbyanalready

infectedperson.AndIalsobelievethatoneismorevulnerabletocoldswhenover‐tired,

understress,orotherwiseinlessthanthebestofhealth.Someofthesebeliefsseemto

meonreflectiontobeinconsistentwithsomeothers;Iseethatitisveryunlikelythatall

ofthemcouldbetrue.Perhapstheycouldbe,butIacknowledgethatthereismuchIdo

notunderstand.IfIsitbackandtrytothinkaboutallmy‘knowledge’ofthecommon

cold,then,Imighteasilycometowonderhowmuchofitreallyamountstoknowledge

andhowmuchdoesnot.WhatdoIreallyknowaboutthecommoncold?IfIwere

sufficientlyinterestedinpursuingthematteritwouldbenaturaltolookintothesourceof

mybeliefs.Hasthereeverbeenanygoodreasonforthinkingthatcoldsareeven

correlatedwithwethairincoldweather,forexample,orwithsittinginadraught?Arethe

peoplefromwhomIlearnedsuchthingslikelytohavebelievedthemforgoodreasons?

Arethosebeliefsjustoldwives'tales,oraretheyreallytrue,andperhapsevenknownto

betruebysomepeople?ThesearequestionsImightaskmyself,andIhaveatleasta

generalideaofhowtogoaboutansweringthem.

(p.3) Apartfrommyimpressionoftheimplausibilityofallmybeliefsaboutthecommon

coldbeingtruetogether,Ihavenotmentionedanyotherreasonforbeinginterestedin

investigatingthestateofmyknowledgeonthatsubject.Butforthemomentthatdoesnot

seemtoaffecttheintelligibilityorthefeasibilityofthereflectiveproject.Thereisnothing

mysteriousaboutit.Itisthesortoftaskwecanbeledtoundertakeforanumberof

reasons,andoftenverygoodreasons,insofaraswehaveverygoodreasonsfor

preferringknowledgeandfirmbelieftoguessworkorwishfulthinkingorsimplytaking

thingsforgranted.

Reflectiononorinvestigationofourputativeknowledgeneednotalwaysextendtoawide

areaofinterest.Itmightbeimportanttoaskwhethersomequitespecificandparticular

thingIbelieveorhavebeentakingforgrantedisreallysomethingIknow.Asamember

ofajuryImightfindthatIhavebeenrulingoutonesuspectinmymindbecausehewas

athousandmilesaway,inCleveland,atthetimeofthecrime.ButImightthenbeginto

askmyselfwhetherthatisreallysomethingthatIknow.Iwouldreflectonthesourceof

mybelief,butreflectioninthiscaseneednotinvolveageneralscrutinyofeverythingI

takemyselftoknowaboutthecase.Re‐examiningtheman'salibiandthecredentialsofits

supportingwitnessesmightbeenoughtosatisfyme.IndeedImightfindthatitsreliability

onthosecountsispreciselywhatIhadbeengoingonallalong.

Inpointingoutthatweareperfectlyfamiliarwiththeideaofinvestigatingorreviewing

ourknowledgeonsomeparticularmatterorinsomegeneralareaIdonotmeanto

suggestthatitisalwayseasytosettlethequestion.Dependingonthenatureofthecase,

itmightbeverydifficult,perhapsevenimpossibleatthetime,toreachafirmconclusion.

Forexample,itwouldprobablybeverydifficultifnotimpossibleformetotraceand

assesstheoriginsofmanyofthosethingsIbelieveaboutthecommoncold.Butitis

equallytruethatsometimesitisnotimpossibleorevenespeciallydifficulttoanswerthe

question.Wedosometimesdiscoverthatwedonotreallyknowwhatwepreviously

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thoughtweknew.ImightfindthatwhatIhadpreviously believedisnoteventrue(p.4)

—thatsittingindraughtsisnotevencorrelatedwithcatchingacold,forexample.OrI

mightfindthatthereisnotorperhapsneverwasanygoodreasontobelievewhatI

believed—thattheman'salibiwasconcoctedandthenfalselytestifiedtobyhisfriends.I

couldreasonablyconcludeineachcasethatI,andeveryoneelseforthatmatter,never

didknowwhatIhadpreviouslythoughtIknew.Weareallfamiliarwiththeordinary

activityofreviewingourknowledge,andwiththeexperienceofreachingapositive

verdictinsomecasesandanegativeverdictinothers.

Descartes'sowninterestinwhatheknowsandhowheknowsitispartofhissearchfor

whathecallsageneralmethodfor‘rightlyconductingreasonandseekingtruthinthe

sciences’.3Hewantsamethodofinquirythathecanbeassuredinadvancewillleadonly

tothetruthifproperlyfollowed.Ithinkwedonotneedtoendorsethewisdomofthat

searchorthefeasibilityofthatprogrammeinordertotrytogoalongwithDescartesin

hisgeneralassessmentofthepositionheisinwithrespecttothethingshebelieves.He

comestofindhisputativeknowledgewantingincertaingeneralrespects,anditisinthe

courseofthatoriginalnegativeassessmentthattheproblemIaminterestedinarises.I

calltheassessment‘negative’becausebytheendofhisFirstMeditationDescartesfinds

thathehasnogoodreasontobelieveanythingabouttheworldaroundhimand

thereforethathecanknownothingoftheexternalworld.

Howisthatassessmentconducted,andhowcloselydoesitparallelthefamiliarkindof

reviewofourknowledgethatweallknowhowtoconductineverydaylife?Thequestion

inoneformoranotherwillbewithusfortherestofthisbook.Itisthequestionofwhat

exactlytheproblemofourknowledgeoftheexternalworldamountsto,andhowitarises

withitsspecialphilosophicalcharacter.Thesourceoftheproblemistobefound

somewherewithinorbehindthekindofthinkingDescartesengagesin.

OnewayDescartes'squestionabouthisknowledgediffersfromtheeverydayexamplesI

consideredisinbeing concernedwith(p.5) everythinghebelievesortakestobetrue.

Howdoesonegoaboutassessingallofone'sknowledgeallatonce?Iwasabletolista

fewofthethingsIbelieveaboutthecommoncoldandthentoaskabouteachofthem

whetherIreallyknowit,andifsohow.ButalthoughIcancertainlylistanumberofthe

thingsIbelieve,andIwouldassenttomanymoreofthemassoonastheywereputto

me,thereobviouslyisnohopeofassessingeverythingIbelieveinthispiecemealway.

Foronething,itprobablymakesnosense,strictlyspeaking,totalkofthenumberof

thingsonebelieves.IfIamaskedwhetheritisoneofmybeliefsthatIwenttoseeafilm

lastnightIcantrulyanswer‘Yes’.IfIwereaskedwhetheritisoneofmybeliefsthatI

wenttothemovieslastnightIwouldgivethesameanswer.HaveItherebyidentified

two,oronlyone,ofmybeliefs?Howisthatquestionevertobesettled?IfwesaythatI

identifiedonlyoneofmybeliefs,itwouldseemthatImustalsobesaidtoholdthe

furtherbeliefthatgoingtoseeafilmandgoingtothemoviesareoneandthesamething.

Sowewouldhavemorethanonebeliefafterall.Theprospectsofarrivingevenata

principleforcountingbeliefs,letaloneatanactualnumberofthem,seemdim.

Evenifitdidmakesensetocountthethingswebelieveitisprettyclearthatthenumber

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wouldbeindefinitelylargeandsoanassessmentofourbeliefsonebyonecouldnever

becompletedanyway.Thisiseasilyseenbyconsideringonlysomeofthesimplestthings

oneknows,forexampleinarithmetic.OnethingIknowisthatoneplusoneequalstwo.

AnotherthingIknowisthatoneplustwoisthree,andanother,thatoneplusthreeis

four.ObviouslytherecouldbenoendtothetaskofassessingmyknowledgeifIhadto

investigateseparatelythesourceofeachoneofmybeliefsinthatseries.AndevenifI

succeededIwouldonlyhaveassessedthethingsIknowabouttheadditionofthe

numberonetoagivennumber;Iwouldstillhavetodothesamefortheadditionoftwo,

andthentheadditionofthree,andsoon.Andeventhatwouldexhaustonlymybeliefs

aboutaddition;allmyothermathematicalbeliefs,nottomentionalltherestofmy

knowledge,wouldremainsofarunexamined.Obviouslythejobcannotbedone

piecemeal,onebyone. Somemethodmustbefoundforassessinglargeclassesof(p.6)

beliefsallatonce.

Onewaytodothiswouldbetolookforcommonsourcesorchannelsorbasesofour

beliefs,andthentoexaminethereliabilityofthosesourcesorbases,justasIexamined

thesourceorbasisofmybeliefthatthesuspectwasinCleveland.Descartesdescribes

suchasearchasasearchfor‘principles’ofhumanknowledge,‘principles’whosegeneral

credentialshecantheninvestigate(HR,145).Ifsome‘principles’arefoundtobe

involvedinallorevenmostofourknowledge,anassessmentofthereliabilityofthose

‘principles’couldbeanassessmentofallormostofourknowledge.IfIfoundgood

reasontodoubtthereliabilityofthesuspect'salibi,forexample,andthatwasallIhadto

gooninmybeliefthathewasinCleveland,thenwhatIearliertooktobemyknowledge

thathewasinClevelandwouldhavebeenfoundwantingorcalledintoquestion.Its

sourceorbasiswouldhavebeenundermined.Similarly,ifoneofthe‘principles’orbases

onwhichallmyknowledgeoftheworlddependswerefoundtobeunreliable,my

knowledgeoftheworldwouldtothatextenthavebeenfoundwantingorcalledinto

questionaswell.

Arethereanyimportant‘principles’ofhumanknowledgeinDescartes'ssense?Ittakes

verylittlereflectiononthehumanorganismtoconvinceusoftheimportanceofthe

senses—sight,hearing,touch,taste,andsmell.Descartesputsthepointmoststrongly

whenhesaysthat‘allthatuptothepresenttimeIhaveacceptedasmosttrueand

certainIhavelearnedeitherfromthesensesorthroughthesenses’(HR,145).Exactly

whathewouldincludeunder‘thesenses’hereisperhapssomewhatindeterminate,but

evenifitisleftvaguemanyphilosopherswoulddenywhatDescartesappearstobe

saying.Theywouldholdthat,forexample,themathematicalknowledgeImentioned

earlierisnotandcouldnotbeacquiredfromthesensesorthroughthesenses,sonot

everythingIknowisknowninthatway.WhetherDescartesisreallydenyingtheviewsof

thosewhobelieveinthenon‐sensorycharacterofmathematicalknowledge,andwhether,

ifhewere,hewouldberight,areissueswecansetasideforthemoment.Itisclearthat

thesensesareatleast(p.7) veryimportantforhumanknowledge.Evenrestricting

ourselvestothetraditionalfivesenseswecanbegintoappreciatetheirimportanceby

reflectingonhowlittlesomeonewouldevercometoknowwithoutthem.Apersonblind

anddeaffrombirthwhoalsolackedtastebudsandasenseofsmellwouldknowvery

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littleaboutanything,nomatterhowlonghelived.Toimaginehimalsoanaesthetizedor

withoutasenseoftouchisperhapstostretchaltogethertoofarone'sconceptionofa

humanorganism,oratleastahumanorganismfromwhomwecanhopetolearn

somethingabouthumanknowledge.Theimportanceofthesensesasasourceorchannel

ofknowledgeseemsundeniable.Itseemspossible,then,toacknowledgetheir

importanceandtoassessthereliabilityofthatsource,quiteindependentlyofthedifficult

questionofwhether ourknowledgecomestousinthatway.Wewouldthenbeall

assessingthecredentialsofwhatisoftencalledour‘sensory’or‘experiential’or

‘empirical’knowledge,andthat,asweshallsee,isquiteenoughtobegoingonwith.

Havingfoundanextremelyimportant‘principle’orsourceofourknowledge,howcanwe

investigateorassess theknowledgewegetfromthatsource?Asbefore,wearefacedall

withtheproblemoftheinexhaustibilityofthethingswebelieveonthatbasis,sono

piecemeal,one‐by‐oneprocedurewilldo.Butperhapswecanmakeasweepingnegative

assessment.Itmightseemthatassoonaswehavefoundthatthesensesareoneofthe

sourcesofourbeliefsweareimmediatelyinapositiontocondemnallputativeknowledge

derivedfromthem.Somephilosophersappeartohavereasonedinthisway,andmany

haveevensupposedthatDescartesisamongthem.TheideaisthatifIamassessingthe

reliabilityofmybeliefsandaskingwhetherIreallyknowwhatItakemyselftoknow,andI

comeacrossalargeclassofbeliefswhichhavecometomethroughthesenses,Ican

immediatelydismissallthosebeliefsasunreliableorasnotamountingtoknowledge

becauseoftheobviousfactthatIcansometimesbewronginmybeliefsbasedonthe

senses.Thingsarenotalwaysastheyappear,soifonthebasisofthewaytheyappearto

meIbelievethattheyreallyareacertainway,Imightstillbewrong.Wehaveallfoundat

onetimeor anotherthatwehavebeenmisledbyappearances;weknowthatthe(p.8)

sensesarenotalwaysreliable.Shouldwenotconclude,then,thatasageneralsourceof

knowledgethesensesarenottobetrusted?AsDescartesputsit,isitnotwisernever

‘totrustentirelytoanythingbywhichwehaveoncebeendeceived’(HR,145)?Don't

wehavehereaquitegeneralwayofcondemningasnotfullyreliable ofourbeliefsall

acquiredbymeansofthesenses?

Ithinktheanswertothatquestionis‘No,wedonot’,andIthinkDescarteswouldagree

withthatanswer.Itistruethathedoestalkofthesenses‘deceiving’usonparticular

occasions,andhedoesaskwhetherthatisnotenoughtocondemnthesensesingeneral

asasourceofknowledge,butheimmediatelyremindsusoftheobviousfactthatthe

circumstancesinwhichthesenses‘deceive’usmightbespecialincertainascertainable

ways,andsotheiroccasionalfailureswouldnotsupportablanketcondemnationoftheir

reliability.

Sometimes,togiveanancientexample,atowerlooksroundfromadistancewhenitis

actuallysquare.Ifwereliedonlyontheappearancesofthemomentwemightsaythatthe

distanttowerisround,andwewouldbewrong.Wealsoknowthattherearemanysmall

organismsinvisibletothenakedeye.Ifthetablebeforemeiscoveredwithsuch

organismsatthemomentbutIlookatitandsaythereisnothingonthetableatall,once

againIwillbewrong.Butallthatfollowsfromthesefamiliarfacts,asDescartespointsout,

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isthattherearethingsaboutwhichwecanbewrong,ortherearesituationsinwhichwe

cangetfalsebeliefs,ifwerelyentirelyonoursensesatthatmoment.Sosometimeswe

shouldbecarefulaboutwhatwebelieveonthebasisofthesenses,orsometimes

perhapsweshouldwithholdourassentfromanystatementabouthowthingsare—when

thingsaretoofarawaytobeseenproperly,forexample,ortoosmalltobeseenatall.

Butthatobviouslyisnotenoughtosupportthepolicyofnevertrustingone'ssenses,or

neverbelievinganythingbasedonthem.NordoesitshowthatIcanneverknow

anythingbymeansofthesenses.Ifmycarstartspromptlyeverymorningfortwoyears

intemperateweatheratsealevelbutthenfailstostart(p.9) onemorninginfreez ing

weatheratthetopofahighmountain,thatdoesnotsupportthepolicyofnevertrusting

mycartostartagainonceIreturntothetemperateloweraltitudefromwhichIso

foolishlytookit.NordoesitshowthatIcanneverknowwhethermycarwilleverstart

again.Itshowsonlythattherearecertaincircumstancesinwhichmyotherwisefully

reliablecarmightnotstart.Sothefactthatwearesometimeswrongor‘deceived’inour

judgementsbasedonthesensesisnotenoughinitselftoshowthatthesensesarenever

tobetrustedandarethereforeneverreliableasasourceofknowledge.

Descartes'snegativeassessmentofallofhissensoryknowledgedoesnotdependonany

suchreasoning.Hestartshisinvestigation,rather,inwhatwouldseemtobethemost

favourableconditionsforthereliableoperationofthesensesasasourceofknowledge.

WhileengagingintheveryphilosophicalreflectionsheiswritingaboutinhisFirst

MeditationDescartesissittinginawarmroom,bythefire,inadressinggown,witha

pieceofpaperinhishand.Hefindsthatalthoughhemightbeabletodoubtthatadistant

towerthatlooksroundreallyisround,itseemsimpossibletodoubtthathereallyis

sittingtherebythefireinhisdressinggownwithapieceofpaperinhishand.Thefireand

thepieceofpaperarenottoosmallortoofarawaytobeseenproperly,theyareright

therebeforehiseyes;itseemstobethebestkindofpositionsomeonecouldbeinfor

gettingreliablebeliefsorknowledgebymeansofthesensesaboutwhatisgoingon

aroundhim.ThatisjusthowDescartesregardsit.Itsbeingabest‐possiblecaseofthat

kindispreciselywhathethinksenableshimtoinvestigateorassessatonefellswoopall

oursensoryknowledgeoftheworldaroundus.Theverdicthearrivesatabouthis

putativeknowledgethatheissittingbythefirewithapieceofpaperinhishandinthat

particularsituationservesasthebasisforacompletelygeneralassessmentofthesenses

asasourceofknowledgeabouttheworldaroundus.

Howcanthatbeso?Howcanhesoeasilyreachageneralverdictaboutallhissensory

knowledgeonthebasisofasingleexample?Obviouslynotsimplybygeneraliz ingfrom

oneparticularexampletoallcasesofsensoryknowledge,asonemightwildlyleaptoa

conclusionaboutallred‐haired(p.10) menonthebasisofoneortwoindividuals.

Rather,hetakestheparticularexampleofhisconvictionthatheissittingbythefirewitha

pieceofpaperinhishandasrepresentativeofthebestpositionanyofuscaneverbein

forknowingthingsabouttheworldaroundusonthebasisofthesenses.Whatistrueof

arepresentativecase,ifitistrulyrepresentativeanddoesnotdependonspecial

peculiaritiesofitsown,canlegitimatelysupportageneralconclusion.Ademonstration

thataparticularisoscelestrianglehasacertainproperty,forexample,canbetakenasa

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demonstrationthatallisoscelestriangleshavethatproperty,aslongastheoriginal

instancewastypicalorrepresentativeofthewholeclass.WhetherDescartes's

investigationofthegeneralreliabilityofthesensesreallydoesfollowthatfamiliarpattern

isadifficultquestion.Whether,orinpreciselywhatsense,theexampleheconsiderscan

betreatedasrepresentativeofourrelationtotheworldaroundusis,Ibelieve,thekey

tounderstandingtheproblemofourknowledgeoftheexternalworld.Butifitturnsout

thatthereisnothingillegitimateaboutthewayhisnegativeconclusionisreached,the

problemwillbeproperlyposed.

ForthemomentIthinkatleastthismuchcanbesaidaboutDescartes'sreasoning.He

choosesthesituationinwhichhefindshimselfasrepresentativeofthebestpositionwe

canbeinforknowingthingsabouttheworldinthesensethat,ifitisimpossibleforhimin

thatpositiontoknowthatheissittingbythefirewithapieceofpaperinhishandthenitis

alsoimpossibleforhiminothersituationstoknowanythingabouttheworldaroundhim

onthebasisofhissenses.Anegativeverdictinthechosencasewouldsupportanegative

verdicteverywhereelse.TheexampleDescartesconsidersisinthatsensemeanttobe

the kindofcasetherecouldbeofsensoryknowledgeabouttheworldaroundus.Ibest

thinkwemustadmitthatitisverydifficulttoseehowDescartesoranyoneelsecouldbe

anybetteroffwithrespecttoknowingsomethingabouttheworldaroundhimonthe

basisofthesensesthanheisinthecaseheconsiders.Butifnoonecouldbeinany

betterpositionforknowing,itseemsnaturaltoconcludethatanynegativeverdict

arrivedataboutthisexample,anydiscoverythatDescartes'sbeliefsinthiscasearenot

reliableordonotamounttoknowledge,could safelybegeneraliz edintoa(p.11)

negativeconclusionaboutallofoursensory‘knowledge’oftheworld.Ifcandidateswith

thebestpossiblecredentialsarefoundwanting,allthosewithlessimpressivecredentials

mustfallshortaswell.

Itwillseematfirstsightthatinconcedingthatthewholequestionturnsonwhether

Descartesknowsinthisparticularcaseweareconcedingverylittle;itseemsobvious

thatDescartesonthatoccasiondoesknowwhathethinksheknowsabouttheworld

aroundhim.ButinfactDescartesfindsthathecannotknowinthiscasethatheissitting

bythefirewithapieceofpaperinhishand.Ifthecaseistrulyrepresentativeofour

sensoryknowledgeingeneral,thatwillshowthatnoonecanknowanythingaboutthe

worldaroundus.Buthowcouldheeverarriveatthatnegativeverdictintheparticular

caseheconsiders?Howcouldanyonepossiblydoubtinsuchacasethatthefireandthe

pieceofpaperarethere?ThepaperisinDescartes'shand,thefireisrighttherebefore

hisopeneyes,andhefeelsitswarmth.Wouldn'tanyonehavetobemadtodenythathe

canknowsomethingaboutwhatisgoingonaroundhiminthosecircumstances?

Descartesfirstanswers‘Yes’.Hesaysthatifheweretodoubtordenyonthatoccasion

thatheissittingbythefirewithapieceofpaperinhishandhewouldbenolessmadthan

thosepauperswhosaytheyarekingsorthosemadmenwhothinktheyarepumpkinsor

aremadeofglass.Buthisreflectionscontinue:

AtthesametimeImustrememberthatIamaman,andthatconsequentlyIamin

thehabitofsleeping,andinmydreamsrepresentingtomyselfthesamethingsor

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sometimesevenlessprobablethings,thandothosewhoareinsaneintheirwaking

moments.HowoftenhasithappenedtomethatinthenightIdreamtthatIfound

myselfinthisparticularplace,thatIwasdressedandseatednearthefire,whilstin

realityIwaslyingundressedinbed!Atthismomentitdoesindeedseemtome

thatitiswitheyesawakethatIamlookingatthispaper;thatthisheadwhichImove

isnotasleep,thatitisdeliberatelyandofsetpurposethatIextendmyhandand

perceiveit;whathappensinsleepdoesnotappearsoclearnorsodistinctasdoes

allthis.ButinthinkingoverthisIremindmyselfthatonmanyoccasionsIhavein

sleepbeendeceivedbysimilarillusions,andindwellingcarefullyonthisreflectionI

seesomanifestlythattherearenocertainindicationsbywhichwemayclearly

distinguishwakefulnessfromsleepthatIamlostinastonishment.Andmy

astonishmentissuchthatitisalmostcapableofpersuadingmethatInowdream.

(HR,145–6.)

(p.12) Withthisthought,ifheisright,Descarteshaslostthewholeworld.Heknows

whatheisexperiencing,heknowshowthingsappeartohim,buthedoesnotknow

whetherheisinfactsittingbythefirewithapieceofpaperinhishand.Itis,forhim,

exactlyasifheweresittingbythefirewithapieceofpaperinhishand,buthedoesnot

knowwhethertherereallyisafireorapieceofpaperthereornot;hedoesnotknow

whatisreallyhappeningintheworldaroundhim.Herealizesthatifeverythinghecan

everlearnaboutwhatishappeningintheworldaroundhimcomestohimthroughthe

senses,buthecannottellbymeansofthesenseswhetherornotheisdreaming,thenall

thesensoryexperiencesheishavingarecompatiblewithhismerelydreamingofaworld

aroundhimwhileinfactthatworldisverydifferentfromthewayhetakesittobe.Thatis

whyhethinkshemustfindsomewaytotellthatheisnotdreaming.Farfromitsbeing

madtodenythatheknowsinthiscase,hethinkshisrecognitionofthepossibilitythathe

mightbedreaminggiveshim‘verypowerfulandmaturelyconsidered’(HR,148)

reasonsforwithholdinghisjudgementabouthowthingsareintheworldaroundhim.He

thinksitiseminentlyreasonabletoinsistthatifheistoknowthatheissittingbythefire

hemustknowthatheisnotdreamingthatheissittingbythefire.Thatisseenasa

necessaryconditionofknowingsomethingabouttheworldaroundhim.Andhefindsthat

thatconditioncannotbefulfilled.Oncarefulreflectionhediscoversthat‘thereareno

certainindicationsbywhichwemayclearlydistinguishwakefulnessfromsleep’.He

concludesthatheknowsnothingabouttheworldaroundhimbecausehecannottellthat

heisnotdreaming;hecannotfulfiloneoftheconditionsnecessaryforknowingsomething

abouttheworld.

TheCartesianproblemofourknowledgeoftheexternalworldthereforebecomes:how

canweknowanythingabouttheworldaroundusonthebasisofthesensesifthesenses

giveusonlywhatDescartessaystheygiveus?Whatwegainthroughthesensesison

Descartes'sviewonlyinformationthatiscompatiblewithourdreamingthingsaboutthe

worldaroundusandnotknowinganythingaboutthatworld.Howthencanweknow

anythingabouttheworldbymeansofthe senses?TheCartesianargument(p.13)

presentsachallengetoourknowledge,andtheproblemofourknowledgeoftheexternal

worldistoshowhowthatchallengecanbemet.

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WhenIspeakhereoftheCartesianargumentorofDescartes'sscepticalconclusionorof

hisnegativeverdictabouthisknowledgeIreferofcourseonlytothepositionhefinds

himselfinbytheendofhisFirstMeditation.Havingatthatpointdiscoveredandstated

theproblemoftheexternalworld,DescartesgoesonintherestofhisMeditationstotry

tosolveit,andbytheendoftheSixthMeditationhethinkshehasexplainedhowhe

knowsalmostallthosefamiliarthingshebeganbyputtinginquestion.SowhenIascribe

toDescartestheviewthatwecanknownothingabouttheworldaroundusIdonot

meantosuggestthatthatishisfinalandconsideredview;itisnothingmorethana

conclusionhefeelsalmostinevitablydriventoattheearlystagesofhisreflections.But

thosearetheonlystagesofhisthinkingIaminterestedinhere.Thatiswherethe

philosophicalproblemofourknowledgeoftheexternalworldgetsposed,andbeforewe

canconsiderpossiblesolutionswemustbesureweunderstandexactlywhatthe

problemis.

Ihavedescribeditasthatofshowingorexplaininghowknowledgeoftheworldaround

usispossiblebymeansofthesenses.Itisimportanttokeepinmindthatthatdemandfor

anexplanationarisesinthefaceofachallengeorapparentobstacletoourknowledgeof

theworld.ThepossibilitythatheisdreamingisseenasanobstacletoDescartes's

knowingthatheissittingbythefire,anditmustbeexplainedhowthatobstaclecaneither

beavoidedorovercome.Itmustbeshownorexplainedhowitispossibleforustoknow

thingsabouttheworld,giventhatthesense‐experienceswegetarecompatiblewithour

merelydreaming.Explaininghowsomethingisneverthelesspossible,despitewhatlooks

likeanobstacletoit,requiresmorethanshowingmerelythatthereisnoimpossibility

involvedinthething—thatitisconsistentwiththeprinciplesoflogicandthelawsofnature

andsointhatsensecouldexist.Themerepossibilityofthestateofaffairsisnotenoughto

settlethequestionofhowourknowledgeoftheworldispossible;wemustunderstand

howtheapparentobstacleistobegotround.

(p.14) Descartes'sreasoningcanbeexaminedandcriticizedatmanydifferentpoints,

andhasbeencloselyscrutinizedbymanyphilosophersforcenturies.Ithasalsobeen

acceptedbymany,perhapsbymorethanwouldadmitorevenrealizethattheyacceptit.

Thereseemstomenodoubtabouttheforceandthefascination—Iwouldsaythealmost

overwhelmingpersuasiveness—ofhisreflections.Thataloneissomethingthatneeds

accountingfor.Icannotpossiblydojusticetoallreasonablereactionstothemhere.In

therestofthisfirstchapterIwanttoconcentrateondeepeningandstrengtheningthe

problemandtryingtolocatemorepreciselythesourceofitspower.

Thereareatleastthreedistinctquestionsthatcouldbepressed.Isthepossibilitythat

Descartesmightbedreamingreallyathreattohisknowledgeoftheworldaroundhim?

Isherightinthinkingthathemustknowthatheisnotdreamingifheistoknow

somethingabouttheworldaroundhim?Andisherightinhis‘discovery’thathecan

neverknowthatheisnotdreaming?IfDescarteswerewrongonanyofthesepointsit

mightbepossibletoavoidtheproblemandperhapseventoexplainwithoutdifficultyhow

weknowthingsabouttheworldaroundus.

Onthefirstquestion,itcertainlyseemsrighttosaythatifDescartesweredreamingthat

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heissittingbythefirewithapieceofpaperinhishandhewouldnotthenknowthatheis

sittingbythefirewithapieceofpaperinhishand.Whenyoudreamthatsomethingis

goingonintheworldaroundyouyoudonottherebyknowthatitis.Mostoften,of

course,whatwedreamisnoteventrue;nooneisactuallychasinguswhenwearelying

asleepinbeddreaming,norareweactuallyclimbingstairs.Butalthoughusuallywhatwe

dreamisnotreallyso,thatisnottherealreasonforourlackofknowledge.Evenif

Descarteswereinfactsittingbythefireandactuallyhadapieceofpaperinhishandat

theverytimehewasdreamingthatheissittingbythefirewithapieceofpaperinhis

hand,hewouldnottherebyknowhewassittingtherewiththatpaper.Hewouldbelikea

certainDukeofDevonshirewho,accordingtoG.E.Moore,oncedreamthewasspeaking

intheHouseofLordsandwokeuptofindthathe speakingintheHouseofwas (p.15)

Lords.4Whathewasdreamingwasinfactso.Butevenifwhatyouaredreamingisinfact

soyoudonottherebyknowthatitis.Evenifweallowthatwhenyouaredreamingthat

somethingissoyoucanbesaid,atleastforthetimebeing,tothinkortobelievethatitis

so,thereisstillnorealconnectionbetweenyourthinkingorbelievingwhatyoudoandits

beingso.Atbestyouhaveathoughtorabeliefwhichjusthappenstobetrue,butthatis

nomorethancoincidenceandnotknowledge.SoDescartes'sfirststepreliesonwhat

seemstobeanundeniablefactaboutdreams:ifyouaredreamingthatsomethingisso

youdonottherebyknowthatitisso.

Thisbaldclaimneedstobequalifiedandmorecarefullyexplained,butIdonotthinkthat

willdiminishtheforceofthepointforDescartes'spurposes.Sometimeswhatisgoingon

intheworldaroundushasaneffectonwhatwedream;forexample,abangingshutter

mightactuallycausemetodream,amongotherthings,thatashutterisbanging.Ifmy

environmentaffectsmeinthatway,andifindreamsIcanbesaidtothinkorbelievethat

somethingisso,wouldInotinthatcaseknowthatashutterisbanging?Itseemstome

thatIwouldnot,butIconfessitisdifficulttosayexactlywhyIthinkso.Thatisprobably

becauseitisdifficulttosayexactlywhatisrequiredforknowledge.Weusetheterm

‘know’confidently,wequiteeasilydistinguishcasesofknowledgefromcasesofits

absence,butwearenotalwaysinapositiontostatewhatwearegoingoninapplyingor

withholdingtheterminthewayswedo.Ithinkthatinthecaseofthebangingshutterit

wouldnotbeknowledgebecauseIwouldbedreaming,Iwouldnotevenbeawake.At

leastitcanbesaid,Ithink,thatevenifDescartes'ssittingbythefirewithapieceofpaper

inhishand(likethebangingshutter)iswhatinfactcauseshimtodreamthatheissitting

bythefirewithapieceofpaperinhishand,thatisstillnohelptohimincomingtoknow

whatisgoingonintheworldaroundhim.Herealiz esthathecouldbedreamingthathe

issittingbythefireevenifheisinfactsittingthere,andthatisthepossibilityhefindshe

hastoruleout.

Ihavesaidthatifyouaredreamingthatsomethingisso youdonotthereby(p.16)

knowthatitisso,anditmightseemasifthatisnotalwaystrue.Supposeamananda

childarebothsleeping.Isayofthechildthatitissoyoungitdoesnotknowwhatseven

timesnineis,whereasthegrownmandoesknowthat.Ifthemanhappensatthatvery

momenttobedreamingthatseventimesnineissixty‐three(perhapsheisdreamingthat

heiscomputinghisincometax),thenheisamanwhoisdreamingthatsomethingisso

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andalsoknowsthatitisso.Thesamekindofthingispossibleforknowledgeaboutthe

worldaroundhim.Hemightbeaphysicistwhoknowsagreatdealaboutthewaythings

arewhichthechilddoesnotknow.Ifthemanalsodreamsthatthingsarethatwayhecan

onceagainbesaidtobedreamingthatsomethingissoandalsotoknowthatitisso.

Thereisthereforenoincompatibilitybetweendreamingandknowing.Thatistrue,butI

donotthinkitaffectsDescartes'sargument.Heisledtoconsiderhowheknowsheisnot

dreamingatthemomentbyreflectingonhowheknowsatthatmomentthatheissitting

bythefirewithapieceofpaperinhishand.Ifheknowsthatatall,hethinks,heknowsit

onthebasisofthesenses.Butherealizesthathishavingthesensoryexperiencesheis

nowhavingiscompatiblewithhismerelydreamingthatheissittingbythefirewitha

pieceofpaperinhishand.Sohedoesnotknowonthebasisofthesensoryexperiences

heishavingatthemomentthatheissittingbythefire.Nor,ofcourse,didthemaninmy

examplesknowthethingshewassaidtoknowonthebasisofthesensoryexperienceshe

washavingatthatmoment.Heknewcertainthingstobeso,andhewasdreamingthose

thingstobeso,butindreamingthemhedidnottherebyknowthemtobeso.

Butaslongasweallowthatthesleepingmandoesknowcertainthingsabouttheworld

aroundhim,evenifhedoesnotknowthemonthebasisoftheverydreamsheishaving

atthemoment,isn'tthatenoughtoshowthatDescartesmustneverthelessbewrongin

hisconclusionthatnoonecanknowanythingabouttheworldaroundhim?No.Itshows

atmostthatwewerehastyorwereignoringDescartes'sconclusioninconcedingthat

someonecouldknowsomethingabouttheworldaroundhim.IfDescartes'sreasoningis

correctthedreamingphysicist,evenwhenheisawake,does(p.17) notreallyknowany

ofthethingswewereuncriticallycreditinghimwithknowingaboutthewaythingsare—

oratleasthedoesnotknowthemonthebasisofthesenses.Inordertoknowthemon

thebasisofthesensestherewouldhavetohavebeenatleastsometimeatwhichhe

knewsomethingaboutwhatwasgoingonaroundhimatthattime.ButifDescartesis

righthecouldnothaveknownanysuchthingunlesshehadestablishedthathewasnot

dreamingatthattime;andaccordingtoDescarteshecouldneverestablishthat.Sothe

factaboutdreamsthatDescartesrelieson—thatonewhodreamsthatsomethingisso

doesnottherebyknowthatitisso—isenoughtoyieldhisconclusioniftheotherstepsof

hisreasoningarecorrect.

WhenhefirstintroducesthepossibilitythathemightbedreamingDescartesseemstobe

relyingonsomeknowledgeabouthowthingsareorwereintheworldaroundhim.He

says‘IremindmyselfthatonmanyoccasionsIhaveinsleepbeendeceivedbysimilar

illusions’,soheseemstoberelyingonsomeknowledgetotheeffectthathehasactually

dreamtinthepastandthatheremembershavingbeen‘deceived’bythosedreams.That

ismorethanheactuallyneedsforhisreflectionsaboutknowledgetohavetheforcehe

thinkstheyhave.Hedoesnotneedtosupporthisjudgementthathehasactuallydreamt

inthepast.Theonlythoughtheneedsisthatitisnowpossibleforhimtobedreaming

thatheissittingbythefire,andthatifthatpossibilitywererealiz edhewouldnotknow

thatheissittingbythefire.OfcourseitwasnodoubttruethatDescarteshaddreamtin

thepastandthathisknowledgethathehaddonesowaspartlywhathewasgoingonin

acknowledgingthepossibilityofhisdreamingonthisparticularoccasion.Butneitherthe

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factofpastdreamsnorknowledgeoftheiractualoccurrencewouldseemtobestrictly

requiredinordertograntwhatDescartesrelieson—thepossibilityofdreaming,andthe

absenceofknowledgeifthatpossibilitywererealiz ed.Thethoughtthathemightbe

dreamingthatheissittingbythefirewithapieceofpaperinhishand,andthefactthatif

hewerehewouldn'tknowhewassittingthere,iswhatgivesDescartespause.That

wouldworryhiminthewayitdoesevenifhehadneveractuallyhadanydreamsexactly

likeit(p.18) inthepast—ifhehadneverdreamtaboutfiresandpiecesofpaperatall.In

fact,Ithinkheneedneverhaveactuallydreamtofanythingbefore,andcertainlyneedn't

knowthatheeverhas,inordertobeworriedinthewayheisbythethoughtthathe

mightbedreamingnow.

ThefactthatthepossibilityofdreamingisallDescartesneedstoappealtobringsout

anothertruthaboutdreamsthathisargumentdependson—thatanythingthatcanbe

goingonorthatonecanexperienceinone'swakinglifecanalsobedreamtabout.This

againisonlyastatementofpossibility—nosensiblepersonwouldsuggestthatwedoat

sometimedreamofeverythingthatactuallyhappenstous,orthateverythingwedream

aboutdoesinfacthappensometime.Butitisveryplausibletosaythatthereisnothing

wecouldnotdreamabout,nothingthatcouldbethecasethatwecouldnotdreamtobe

thecase.Isayitisveryplausible;ofcourseIcannotproveittobetrue.Butevenifitis

nottruewithcompletegenerality,wemustsurelygrantthatitispossibletodreamthat

oneissittingbyafirewithapieceofpaperinone'shand,andpossibletodreamof

countlessotherequallyobviousandequallymundanestatesofaffairsaswell,andthose

possibilitiesarewhatDescartesseesasthreateningtohisknowledgeoftheworldaround

him.

Thereseemslittlehope,then,ofobjectingthatitissimplynotpossibleforDescartesto

dreamthatheissittingbythefirewithapieceofpaperinhishand.Norisitanymore

promisingtosaythatevenifheweredreamingitwouldnotfollowthathedidnotknow

thathewassittingthere.IthinkboththosestepsorassumptionsofDescartes's

reasoningareperfectlycorrect,andfurtherdefenceofthematthisstageisunnecessary.

Ifhisargumentandtheproblemtowhichitgivesrisearetobeavoided,itmightseem

thatthebesthopeisthereforetoaccepthischallengeandshowthatitcanbemet.That

wouldbeineffecttoarguethatDescartes'salleged‘discovery’isnodiscoveryatall:we

cansometimesknowthatwearenotdreaming.

Thiscaneasilyseemtobethemoststraightforwardandmostpromisingstrategy.It

allowsthatDescartesisrightinthinkingthatknowingthatoneisnotdreamingisa

condition(p.19) ofknowingsomethingabouttheworldaroundus,butwronginthinking

thatthatconditioncanneverbemet.Andthatcertainlyseemsplausible.Surelyitisnot

impossibleformetoknowthatIamnotdreaming?Isn'tthatsomethingIoftenknow,and

isn'titsomethingIcansometimesfindoutifthequestionarises?Ifitis,thenthefactthat

ImustknowthatIamnotdreamingifIamtoknowanythingabouttheworldaroundme

willbenothreattomyknowledgeoftheworld.

Howeverobviousandundeniableitmightbethatweoftendoknowthatwearenot

dreaming,IthinkthisstraightforwardresponsetoDescartes'schallengeisatotalfailure.

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IncallingitstraightforwardImeanthatitacceptsDescartes'sconditionsforknowledgeof

theworldandtriestoshowthattheycanbefulfilled.ThatiswhatIthinkcannotbedone.

Toputthesamepointinanotherway:IthinkDescarteswouldbeperfectlycorrectin

saying‘therearenocertainindicationsbywhichwemayclearlydistinguishwakefulness

fromsleep’,andsowecouldnevertellwearenotdreaming, hewerealsorightthatif

knowingthatoneisnotdreamingisaconditionofknowingsomethingabouttheworld

aroundus.ThatiswhyIthinkonecannotacceptthatconditionandthengoontoestablish

thatoneisnotdreaming.IdonotmeantobesayingsimplythatDescartesisright—that

wecanneverknowthatwearenotdreaming.ButIdowanttoarguethateitherwecan

neverknowthatwearenotdreamingorelsewhatDescartessaysisaconditionof

knowingthingsabouttheworldisnotreallyaconditioningeneralofknowingthingsabout

theworld.Thestraightforwardstrategydeniesbothalternatives.Iwilltrytoexplainwhy

Ithinkwemustacceptonealternativeortheother.

WhenDescartesaskshimselfhowheknowsthatheissittingbythefirewithapieceof

paperinhishandwhydoesheimmediatelygoontoaskhimselfhowheknowsheisnot

dreamingthatheissittingbythefirewithapieceofpaperinhishand?Ihavesuggested

thatitisbecauseherecognizesthatifheweredreaminghewouldnotknowonthebasis

ofhissensesatthemomentthatheissittingthere,andsohethinkshemustknowthat

thatpossibilitydoesnotobtainifheistoknowthatheisinfactsittingthere. But(p.20)

thisparticularexamplewaschosen,notforanypeculiaritiesitmightbethoughtto

possess,butbecauseitcouldbetakenastypicalofthebestpositionwecaneverbein

forcomingtoknowthingsabouttheworldaroundusonthebasisofthesenses.Whatis

trueofthiscasethatisrelevanttoDescartes'sinvestigationofknowledgeissupposedto

betrueofallcasesofknowledgeoftheworldbymeansofthesenses;thatiswhythe

verdictarrivedatherecanbetakentobetrueofoursensoryknowledgegenerally.But

whatDescartesthinksistrueofthisparticularcaseofsensoryknowledgeoftheworldis

thathemustknowheisnotdreamingifheistoknowthatheissittingbythefirewitha

pieceofpaperinhishand.Thatisrequired,notbecauseofanypeculiaritiesofthis

particularcase,butpresumablybecause,accordingtoDescartes,itisanecessary

conditionofanycase—evenabestpossiblecase—ofknowledgeoftheworldbymeansof

thesenses.ThatiswhyIascribedtoDescartesthequitegeneralthesisthatknowingthat

oneisnotdreamingisaconditionofknowingsomethingabouttheworldarounduson

thebasisofthesenses.Sincehethinksthepossibilityofhisdreamingmustberuledout

inthecaseheconsiders,andthecaseheconsidersisregardedastypicalandwithout

specialcharacteristicsofitsown,hethinksthatthepossibilitythatheisdreamingmustbe

ruledoutineverycaseofknowingsomethingabouttheworldbymeansofthesenses.

Ifthatreallyisaconditionofknowingsomethingabouttheworld,Ithinkitcanbeshown

thatDescartesisrightinholdingthatitcanneverbefulfilled.Thatiswhatthe

straightforwardresponsedenies,andthatiswhyIthinkthatresponsemustbewrong.

WecannotacceptthetermsofDescartes'schallengeandthenhopetomeetit.

SupposeDescartestriestodeterminethatheisnotdreaminginordertofulfilwhathe

seesasanecessaryconditionofknowingthatheissittingbythefirewithapieceofpaper

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inhishand.Howishetoproceed?Herealizesthathisseeinghishandandseeingand

feelingapieceofpaperbeforehimandfeelingthewarmthofthefire—infacthisgettingall

thesensoryexperiencesorallthesensoryinformationheisthengetting—issomething

thatcouldbehappeningeven(p.21) ifheweredreaming.Toestablishthatheisnot

dreaminghewouldthereforeneedsomethingmorethanjustthoseexperiencesorthat

informationalone.Hewouldalsoneedtoknowwhetherthoseexperiencesandthat

informationarereliable,notmerelydreamt.Ifhecouldfindsomeoperationortest,orif

hecouldfindsomecircumstanceorstateofaffairs,thatindicatedtohimthathewasnot

dreaming,perhapshecouldthenfulfilthecondition—hecouldknowthathewasnot

dreaming.Buthowcouldatestoracircumstanceorastateofaffairsindicatetohimthat

heisnotdreamingifaconditionofknowinganythingabouttheworldisthatheknowheis

notdreaming?Itcouldnot.Hecouldneverfulfilthecondition.

Letussupposethatthereisinfactsometestwhichapersoncanperformsuccessfully

onlyifheisnotdreaming,orsomecircumstanceorstateofaffairswhichobtainsonlyif

thatpersonisnotdreaming.Ofcourseforthattestorstateofaffairstobeofanyuseto

himDescarteswouldhavetoknowofit.Hewouldhavetoknowthatthereissuchatest

orthatthereisastateofaffairsthatshowsthatheisnotdreaming;withoutsuch

informationhewouldbenobetterofffortellingthatheisnotdreamingthanhewouldbe

iftherewerenosuchtestorstateofaffairsatall.Tohaveacquiredthatinformationhe

wouldatsometimehavetohaveknownmorethanjustsomethingaboutthecourseof

hissensoryexperience,sincetheconnectionbetweentheperformanceofacertaintest,

orbetweenacertainstateofaffairs,andsomeone'snotdreamingisnotitselfjustafact

aboutthecourseofthatperson'ssensoryexperience;itisafactabouttheworldbeyond

hissensoryexperiences.Nowstrictlyspeakingifitisaconditionofknowinganything

abouttheworldbeyondone'ssensoryexperiencesthatoneknowthatoneisnot

dreaming,thereisanobviousobstacletoDescartes'severhavinggottheinformationhe

needsaboutthattestorstateofaffairs.Hewouldhavetohaveknownatsometimethat

hewasnotdreaminginordertogettheinformationheneedstotellatanytimethatheis

notdreaming—andthatcannotbedone.

ButsupposeweforgetaboutthisdifficultyandconcedethatDescartesdoesindeed

know(somehow)thatthereis atestorcircumstanceorstateofaffairsthat(p.22)

unfailinglyindicatesthatheisnotdreaming.Still,thereisanobstacletohiseverusingthat

testorstateofaffairstotellthatheisnotdreamingandtherebyfulfillingtheconditionfor

knowledgeoftheworld.Thetestwouldhavetobesomethinghecouldknowhehad

performedsuccessfully,thestateofaffairswouldhavetobesomethinghecouldknow

obtains.Ifhecompletelyunwittinglyhappenedtoperformthetest,orifthestateofaffairs

happenedtoobtainbuthedidn'tknowthatitdid,hewouldbeinnobetterpositionfor

tellingwhetherhewasdreamingthanhewouldbeifhehaddonenothingordidnoteven

knowthattherewassuchatest.Buthowishetoknowthatthetesthasbeenperformed

successfullyorthatthestateofaffairsinquestiondoesinfactobtain?Anythingonecan

experienceinone'swakinglifecanalsobedreamtabout;itispossibletodreamthatone

hasperformedacertaintestordreamthatonehasestablishedthatacertainstateof

affairsobtains.And,aswehaveseen,todreamthatsomethingabouttheworldaround

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youissoisnottherebytoknowthatitisso.Inordertoknowthathistesthasbeen

performedorthatthestateofaffairsinquestionobtainsDescarteswouldthereforehave

toestablishthatheisnotmerelydreamingthatheperformedthetestsuccessfullyor

thatheestablishedthatthestateofaffairsobtains.Howcouldthatinturnbeknown?

Obviouslytheparticulartestorstateofaffairsalreadyinquestioncannotserveasa

guaranteeofitsownauthenticity,sinceitmighthavebeenmerelydreamt,sosome

furthertestorstateofaffairswouldbeneededtoindicatethattheoriginaltestwas

actuallyperformedandnotmerelydreamt,orthatthestateofaffairsinquestionwas

actuallyascertainedtoobtainandnotjustdreamttoobtain.Butthisfurthertestorstate

ofaffairsissubjecttothesamegeneralconditioninturn.Everypieceofknowledgethat

goesbeyondone'ssensoryexperiencesrequiresthatoneknowoneisnotdreaming.

ThissecondtestorstateofaffairswillthereforebeofuseonlyifDescartesknowsthathe

isnotmerelydreamingthatheisperformingorascertainingit,sincemerelytodream

thathehadestablishedtheauthenticityofthefirsttestisnottohaveestablishedit.And

soon.Atnopointcanhefindatestfor notdreamingwhichhecanknowhasbeen(p.23)

successfullyperformedorastateofaffairscorrelatedwithnotdreamingwhichhecan

knowobtains.HecanthereforeneverfulfilwhatDescartessaysisanecessarycondition

ofknowingsomethingabouttheworldaroundhim.Hecanneverknowthatheisnot

dreaming.

Imustemphasizethatthisconclusionisreachedonlyontheassumptionthatitisa

conditionofknowinganythingabouttheworldaroundusonthebasisofthesensesthat

weknowwearenotdreamingthatthethingisso.Ithinkitishisacceptanceofthat

conditionthatleadsDescartesto‘seesomanifestlythattherearenocertainindications

bywhichwemayclearlydistinguishwakefulnessfromsleep’.AndIthinkDescartesis

absolutelyrighttodrawthatconclusion,givenwhathethinksisaconditionofknowledge

oftheworld.ButallIhavearguedonDescartes'sbehalf(heneverspellsouthis

reasoning)isthatwecannotbothacceptthatconditionofknowledgeandhopetofulfilit,

asthestraightforwardresponsehopestodo.Andofcourseifoneofthenecessary

conditionsofknowledgeoftheworldcanneverbefulfilled,knowledgeoftheworld

arounduswillbeimpossible.

IthinkwehavenowlocatedDescartes'sreasonforhisnegativeverdictaboutsensory

knowledgeingeneral.Ifweagreethathemustknowthatheisnotdreamingifheisto

knowinhisparticularcasethatheissittingbythefirewithapieceofpaperinhishand,

wemustalsoagreethatwecanknownothingabouttheworldaroundus.

OncewerecognizethattheconditionDescartestakesasnecessarycanneverbefulfilled

ifheisrightinthinkingitisindeednecessary,wearenaturallyledtothequestion

whetherDescartesisright.Isitreallyaconditionofknowingsomethingabouttheworld

thatoneknowoneisnotdreaming?ThatisthesecondofthethreequestionsI

distinguished.Itistheonethathasreceivedtheleastattention.InaskingitnowIdonot

meantobegoingbackonsomethingIsaidearlierwasundeniablytrue,viz.,thatifoneis

dreamingthatsomethingabouttheworldissoonedoesnottherebyknowthatitisso.

Thatstillseemstomeundeniable,butitisnotthesameasDescartes'sassumptionthat

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one mustknowthatoneisnotdreamingifoneistoknowsomethingaboutthe(p.24)

world.Theundeniabletruthsaysonlythatyoulackknowledgeifyouaredreaming;

Descartessaysthatyoulackknowledgeifyoudon'tknowthatyouarenotdreaming.

Onlywiththestrongerassumptioncanhisscepticalconclusionbereached.

Isthatassumptiontrue?InsofaraswefindDescartes'sreasoningconvincing,oreven

plausible,Ithinkitisbecausewetooonreflectionfindthatitistrue.Isaidthatnotmuch

attentionhadbeenpaidtothatparticularpartofDescartes'sreasoning,andIthinkthat

tooisbecause,ashepresentsit,thestepseemsperfectlyconvincingandsoonlyother

partsoftheargumentappearvulnerable.Whyisthatso?IsitbecauseDescartes's

assumptionisindeedtrue?Isthereanythingwecandothatwouldhelpusdetermine

whetheritistrueornot?ThequestionisimportantbecauseIhavearguedsofarthatifit

istruewecanneverknowanythingabouttheworldaroundusonthebasisofthe

senses,andphilosophicalscepticismabouttheexternalworldiscorrect.Wewouldhave

tofindthatconclusionasconvincingorasplausibleaswefindtheassumptionfromwhich

itisderived.

GivenouroriginalfavourableresponsetoDescartes'sreasoning,then,itcanscarcelybe

deniedthatwhatIhavecalledhisassumptionorcondition perfectlynaturaltoseems

insiston.Perhapsitseemslikenothingmorethananinstanceofafamiliarcommonplace

aboutknowledge.Weareallawarethat,eveninthemostordinarycircumstanceswhen

nothingveryimportantturnsontheoutcome,wecannotknowaparticularthingunless

wehaveruledoutcertainpossibilitiesthatwerecogniz eareincompatiblewithour

knowingthatthing.

SupposethatonlookingoutthewindowIannouncecasuallythatthereisagoldfinchin

thegarden.IfIamaskedhowIknowitisagoldfinchandIreplythatitisyellow,weall

recogniz ethatinthenormalcasethatisnotenoughforknowledge.‘Forallyou'vesaidso

far,’itmightbereplied,‘thethingcouldbeacanary,sohowdoyouknowit'sa

goldfinch?’.AcertainpossibilitycompatiblewitheverythingIhavesaidsofarhasbeen

raised,andifwhat(p.25) IhavesaidsofarisallIhavegottogoonandIdon'tknow

thatthethinginthegardenisnotacanary,thenIdonotknowthatthereisagoldfinchin

thegarden.ImustbeabletoruleoutthepossibilitythatitisacanaryifIamtoknowthat

itisagoldfinch.Anyonewhospeaksaboutknowledgeandunderstandswhatotherssay

aboutitwillrecogniz ethisfactorconditioninparticularcases.

Inthisexamplewhatissaidtobepossibleissomethingincompatiblewiththetruthof

whatIclaimtoknow—ifthatbirdwereacanaryitwouldnotbeagoldfinchinthegarden,

butacanary.WhatIbelieveinbelievingitisagoldfinchwouldbefalse.Butthatisnotthe

onlywayapossibilitycanworkagainstmyknowledge.IfIcometosuspectthatallthe

witnesseshaveconspiredandmadeupastoryabouttheman'sbeinginClevelandthat

night,forexample,andtheirtestimonyisallIhavegottogooninbelievingthathewasin

Cleveland,ImightfindthatInolongerknowwhetherhewasthereornotuntilIhave

somereasontoruleoutmysuspicion.IftheirtestimonywereallinventedIwouldnot

knowthatthemanwasinCleveland.ButstrictlyspeakinghisbeinginClevelandisnot

incompatiblewiththeirmakingupastorysayinghewas.Theymighthaveinventeda

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storytoprotecthim,whereasinfact,unknowntothem,hewasthereallthetime.Sucha

complicatedplotisnotnecessarytobringoutthepoint;Moore'sDukeofDevonshireis

enough.FromthefactthathewasdreamingthathewasspeakingintheHouseofLords

itdidnotfollowthathewasnotspeakingintheHouseofLords.Infacthewas.The

possibilityofdreaming—whichwasactualinthatcase—didnotimplythefalsityofwhat

wasbelieved.Apossibledeficiencyinthebasisofmybeliefcaninterferewithmy

knowledgewithoutitselfrenderingfalsetheverythingIbelieve.Ahallucinogenicdrug

mightcausemetoseemybedcoveredwithahugepileofleaves,forexample.5Having

takenthatdrug,IwillknowtheactualstateofmybedonlyifIknowthatwhatIseeisnot

justtheeffectofthedrug;ImustbeabletoruleoutthepossibilitythatIamhallucinating

thebedandtheleaves.Buthoweverimprobable itmightbethatmybedis(p.26)

actuallycoveredwithleaves,itsnotbeingcoveredwithleavesdoesnotfollowfromthe

factthatIamhallucinatingthatitis.WhatIamhallucinatingcouldneverthelessbe

(unknowntome)true.Butagoldfinchsimplycouldnotbeacanary.Soalthoughthereare

twodifferentwaysinwhichacertainpossibilitycanthreatenmyknowledge,itremains

truethattherearealwayscertainpossibilitieswhichmustbeknownnottoobtainifIam

toknowwhatIclaimtoknow.

Ithinkthesearejustfamiliarfactsabouthumanknowledge,somethingweallrecognize

andabidebyinourthoughtandtalkaboutknowingthings.Weknowwhatwouldbea

validchallengetoaclaimtoknowsomething,andwecanrecognizetherelevanceand

forceofobjectionsmadetoourclaimstoknow.Thequestionbeforeusistowhatextent

Descartes'sinvestigationofhisknowledgethatheissittingbythefirewithapieceof

paperinhishandfollowstheserecognizedeverydayproceduresforassessingclaimsto

know.Ifitdoesfollowthemfaithfully,andyetleadstotheconclusionthathecannotknow

whereheisorwhatishappeningaroundhim,weseemforcedtoaccepthisnegative

conclusionaboutknowledgeingeneraljustasweareforcedtoaccepttheconclusionthat

IdonotknowitisagoldfinchordonotknowthewitnesswasinClevelandbecauseI

cannotruleoutthepossibilitieswhichmustberuledoutifIamtoknowsuchthings.Is

Descartes'sintroductionofthepossibilitythathemightbedreamingjustlikethe

introductionofthepossibilitythatitmightbeacanaryinthegardenorthatthealibimight

becontrivedorthatitmightbeahallucinationofmybedcoveredwithleaves?

ThosepossibilitieswereallsuchthatiftheyobtainedIdidnotknowwhatIclaimedto

know,andtheyhadtobeknownnottoobtaininorderfortheoriginalknowledge‐claimto

betrue.DoesDescartes'sdream‐possibilityfulfilbothofthoseconditions?Ihavealready

saidthatitseemsundeniablethatitfulfilsthefirst.Ifhe dreamingDescarteswouldwere

notknowwhatheclaimstoknow.Someonewhoisdreamingdoesnottherebyknow

anythingabouttheworldaroundhimeveniftheworldaroundhimhappenstobejust

thewayhedreamsorbelievesittobe.Sohisdreamingisincompatible withhis(p.27)

knowing.Butdoesitfulfilthesecondcondition?Isitapossibilitywhichmustbeknownnot

toobtainifDescartesistoknowthatheissittingbythefirewithapieceofpaperinhis

hand?Ithinkitisdifficultsimplytodenythatitis.TheevidentforceofDescartes's

reasoningwhenwefirstencounteritisenoughtoshowthatitcertainlystrikesusasa

relevantpossibility,assomethingthatheshouldknownottoobtainifheistoknowwhere

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heisandwhatishappeningaroundhim.

WhenthatpossibilitystrikesusasobviouslyrelevantinDescartes'sinvestigationwe

mightcometothinkthatitisbecauseofasimpleandobviousfactaboutknowledge.In

thecaseofthegoldfinchweimmediatelyrecognizethatImustknowthatitisnotacanary

ifIamtoknowitisagoldfinch.Anditisverynaturaltothinkthatthatissimplybecauseits

beingacanaryisincompatiblewithitsbeingagoldfinch.Ifitwereacanaryitwouldnotbe

agoldfinch,andIwouldthereforebewronginsayingthatitis;soifIamtoknowitisa

goldfinchImustruleoutthepossibilitythatitisacanary.Theideaisthatthetwo

conditionsIdistinguishedinthepreviousparagrapharenotreallyseparateafterall.As

soonasweseethatacertainpossibilityisincompatiblewithourknowingsuch‐and‐such,it

issuggested,weimmediatelyrecognizethatitisapossibilitythatmustbeknownnotto

obtainifwearetoknowthesuch‐and‐suchinquestion.Weseethatthedream‐possibility

satisfiesthatfirstconditioninDescartes'scase(ifheweredreaming,hewouldn'tknow),

andthatiswhy,accordingtothissuggestion,weimmediatelyseethatitisrelevantand

mustberuledout.Somethingweallrecognizeaboutknowledgeiswhatissaidtomake

thatobvioustous.

Butisthe‘simpleandobviousfactaboutknowledge’appealedtointhisexplanationreally

somethingthatistrueofhumanknowledgeeveninthemostordinarycircumstances?

Whatexactlyisthe‘fact’inquestionsupposedtobe?Ihavedescribeditsofar,asapplied

tothecaseofthegoldfinch,asthefactthatifIknowsomething (it'sagoldfinch)Imustp

knowthefalsityofallthosethingsincompatiblewithp(e.g.,it'sacanary).Iftherewere

oneofthosethingsthatIdidnotknowtobefalse,anditwereinfacttrue,Iwouldnot

knowthatp,sinceinthatcasesomething incompatiblewith(p.28) pwouldbetrueand

so wouldnotbetrue.ButtosaythatImustknowthatallthosethingsincompatiblewithp

parefalseisthesameassayingthatImustknowthetruthofallthosethingsthatmust

betrueifpistrue.Anditisextremelyimplausibletosaythatthatisa‘simpleandobvious

fact’weallrecognizeabouthumanknowledge.

Thedifficultyisthattherearenodeterminatelimitstothenumberofthingsthatfollow

fromthethingsIalreadyknow.ButitcannotbesaidthatInowknowallthose

indeterminatelymanythings,althoughtheyallmustbetrueifthethingsthatIalready

knowaretrue.EvengrantingthatInowknowagreatdealaboutalotofdifferentthings,

myknowledgeobviouslydoesnotextendtoeverythingthatfollowsfromwhatInow

know.Ifitdid,mathematics,totakeonlyoneexample,wouldbeagreatdealeasierthanit

is—orelseimpossiblydifficult.Inknowingthetruthofthesimpleaxiomsofnumber

theory,forexample,Iwouldtherebyknowthetruthofeverythingthatfollowsfrom

them;everytheoremofnumbertheorywouldalreadybeknown.Or,takingthe

pessimisticside,sinceobviouslynoonedoesknowallthetheoremsofnumbertheory,it

wouldfollowthatnooneevenknowsthatthosesimpleaxiomsaretrue.

Itisabsurdtosaythatweenjoyorrequiresuchvirtualomniscience,soitismore

plausibletoholdthatthe‘simpleandobviousfact’weallrecogniz eaboutknowledgeis

theweakerrequirementthatwemustknowthefalsityofallthosethingsthatwe toknow

beincompatiblewiththethingsweknow.Iknowthatabird'sbeingacanaryis

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incompatiblewithitsbeingagoldfinch;thatisnotsomefar‐flung,unknownconsequence

ofitsbeingagoldfinch,butsomethingthatanyonewouldknowwhoknewanythingabout

goldfinchesatall.AndtheideaisthatthatiswhyImustknowthatitisnotacanaryifIam

toknowthatitisagoldfinch.Perhaps,inordertoknowsomething,p,Idonotneedto

knowthefalsityofallthosethingsthatareincompatiblewithp,butitcanseemthatat

leastImustknowthefalsityofallthosethingsthatIknowtobeincompatiblewith .Sincep

Iclaimtoknowthatthebirdisagoldfinch,andIknowthatitsbeingagoldfinchimplies

thatitisnotacanary,(p.29) Imustforthatreasonknowthatitisnotacanaryifmy

originalclaimistrue.InclaimingtoknowitisagoldfinchIwas,sotospeak,committing

myselftoknowingthatitisnotacanary,andImusthonourmycommitments.

Thisrequirementasitstands,evenifitdoesexplainwhyImustknowthatthebirdisnot

acanary,doesnotaccountfortherelevanceoftheothersortsofpossibilitiesIhave

mentioned.ThereasoninthegoldfinchcasewassaidtobethatIknowthatitsbeinga

canaryisincompatiblewithitsbeingagoldfinch.ButthatwillnotexplainwhyImustrule

outthepossibilitythatthewitnesseshaveinventedastoryabouttheman'sbeingin

Cleveland,orthepossibilitythatIamhallucinatingmybedcoveredwithapileofleaves.

NorwillitexplainwhyDescartesmustruleoutthepossibilitythatheisdreaming.WhatI

claimedtoknowinthefirstcaseisthatthemanwasinClevelandthatnight.But,aswe

sawearlier,itisnotaconsequenceofhisbeinginClevelandthatnoonewillinventastory

totheeffectthathewasinCleveland;theymightmistakenlybelievehewasnotthereand

thentellwhattheythinkisalie.Norisitaconsequenceofmybed'sbeingcoveredwith

leavesthatIamnothallucinatingthatitis.Butwerecognizethatinordertoknowinthose

casesIneverthelesshadtoruleoutthosepossibilities.Similarly,astheDukeof

Devonshireremindsus,itisnotaconsequenceofDescartes'ssittingbythefirewitha

pieceofpaperinhishandthatheisnotdreamingthatheis.Soifitisobvioustousthat

Descartesmustknowthatheisnotdreamingifheistoknowthatheissittingbythefire,

itcannotbesimplybecausethepossibilityinquestionisknowntobeincompatiblewith

whatheclaimstoknow.Itisnot.

Ifthereissome‘simpleandobviousfactaboutknowledge’thatwerecognizeandrelyon

inrespondingtoDescartes'sreasoningitmustthereforebemorecomplicatedthanwhat

hasbeensuggestedsofar.Reflectingevenontheuncontroversialeverydayexamples

alonecaneasilyleadustosupposethatitissomethinglikethis:ifsomebodyknows

something,p,hemustknowthefalsityofallthosethingsincompatiblewithhisknowing

thatp(orperhapsallthosethingsheknowstobeincompatiblewithhisknowingthat

(p.30) p).Iwillnotspeculatefurtheronthequalificationsoremendationsneededto

maketheprinciplelessimplausible.Thequestionnowiswhetheritisouradherenceto

anysuchprincipleorrequirementthatisresponsibleforourrecognitionthatthe

possibilitythatthebirdisacanaryorthepossibilitythatthewitnessesmadeupastory

mustbeknownnottoobtainifIamtoknowthethingsIsaidIknewinthosecases.What

exactlyaretheproceduresorstandardswefollowinthemostordinary,humdrumcases

ofputativeknowledge?ReflectiononthesourceofDescartes'sscepticalreasoninghas

ledtodifficultiesindescribingandthereforeinunderstandingeventhemostfamiliar

procedureswefollowineverydaylife.Thatisoneoftherewardsofastudyof

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The Problem of the External World
UniversityPressScholarshipOnline OxfordScholarshipOnline
TheSignificanceofPhilosophicalScepticism BarryStroud
Printpublicationdate:1984
PrintISBN-13:9780198247616
PublishedtoOxfordScholarshipOnline:November2003
DOI:10.1093/0198247613.001.0001
TheProblemoftheExternalWorld
BarryStroud(ContributorWebpage)
DOI:10.1093/0198247613.003.0001 AbstractandKeywords
Chapter1setsouttheProblemoftheExternalWorldtowhichscepticismisanatural
response:theproblem,firstposedbyDescartesinhisFirstMeditation,ofhowtoshow
thatwehaveanyknowledgeabouttheworldaroundus.
Reflectingonthenatureofhissensoryexperiences,Descartesfindshimselfunableto
ruleoutthepossibilitythatheisdreamingand,onthataccount,driventothedevastating
conclusionthatheknowsnothingatallabouttheworldaroundhim.Stroudarguesthatif
Descartesisrighttoinsistthatinordertoknowsomethingabouttheworldaroundhim
hemustknowthatheisnotdreaming,thenheisalsorightthathehasnosuch
knowledge,becausetheconditionforknowledgethatDescartesacceptscanneverbe
fulfilled:fulfillingitwouldrequireknowledgewhichitselfwouldbepossibleonlyifthe conditionwerefulfilled. Page 1 of 27
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The Problem of the External World
Themorepromisingstrategyinthefaceofthescepticalargument,therefore,isto
examinemorecarefullytherequirementthatwemustknowthatwearenotdreamingif
wearetoknowanythingabouttheworldaroundus.
Butifthatrequirementisafactofourordinaryconceptionofknowledge,asitseemsto
be,wemustacceptit,becausethereisnonotionofknowledgeotherthantheordinary
onethatisembodiedintheproceduresandpracticesofeverydayandscientificlife;and
unlesswefindawayofrejectingtheproblemaltogether,wewillhavetoacceptwithitthe
conclusionthatnooneknowsanythingaboutworldaroundus.
Keywords:conditionsofknowledge,Descartes,dreaming,FirstMeditation,ordinaryconceptionof
knowledge,Possibilityofknowledge,ProblemoftheExternalWorld,rejectionoftheproblem,sc eptical
argument,sc epticalexperienc e
SinceatleastthetimeofDescartesintheseventeenthcenturytherehasbeena
philosophicalproblemaboutourknowledgeoftheworldaroundus.1Putmostsimply,
theproblemistoshowhowwecanhaveanyknowledgeoftheworldatall.Theconclusion
thatwecannot,thatnooneknowsanythingabouttheworldaroundus,iswhatIcall
‘scepticismabouttheexternalworld’,sowecouldalsosaythattheproblemistoshow
howorwhyscepticismabouttheexternalworldisnotcorrect.Myaimisnottosolvethe
problembuttounderstandit.Ibelievetheproblemhasnosolution;orratherthatthe
onlyanswertothequestionasitismeanttobeunderstoodisthatwecanknownothing
abouttheworldaroundus.Buthowisthequestionmeanttobeunderstood?Itcanbe
expressedinafewEnglishwordsfamiliartoallofus,butIhopetoshowthatan
understandingofthespecialphilosophicalcharacterofthequestion,andofthe
inevitabilityofanunsatisfactoryanswertoit,cannotbeguaranteedbyour
understandingofthosewordsalone.Toseehowtheproblemismeanttobeunderstood
wemustthereforeexaminewhatisperhapsbestdescribedasitssource—howthe
problemarisesandhowitacquiresthatspecialcharacterthatmakesanunsatisfactory
negativeanswerinevitable.Wemusttrytounderstandthephilosophicalproblemofour
knowledgeoftheexternalworld.
TheproblemaroseforDescartesinthecourseofreflectingoneverythingheknows.He
reachedapointinhislifeatwhichhetriedtositbackandreflectoneverythinghehad
everbeentaughtortold,everythinghehadlearnedordiscoveredorbelievedsincehe
wasoldenoughtoknowor(p.2) believeanything.2Wemightsaythathewasreflecting
onhisknowledge,butputtingitthatwaycouldsuggestthatwhathewasdirectinghis
attentiontowasindeedknowledge,andwhetheritwasknowledgeornotisprecisely
whathewantedtodetermine.‘AmongallthethingsIbelieveortaketobetrue,what
amountstoknowledgeandwhatdoesnot?’;thatisthequestionDescartesaskshimself.It
isobviouslyaverygeneralquestion,sinceitasksabouteverythinghebelievesortakes
tobetrue,butinotherrespectsitsoundsjustlikethesortofquestionweareperfectly
familiarwithineverydaylifeandoftenknowhowtoanswer.
Forexample,Ihavecometoacceptovertheyearsagreatmanythingsaboutthe
commoncold.Ihavealwaysbeentoldthatonecancatchcoldbygettingwetfeet,orfrom Page 2 of 27
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The Problem of the External World
sittinginadraught,orfromnotdryingone'shairbeforegoingoutdoorsincoldweather.
Ihavealsolearnedthatthecommoncoldistheeffectofavirustransmittedbyanalready
infectedperson.AndIalsobelievethatoneismorevulnerabletocoldswhenover‐tired,
understress,orotherwiseinlessthanthebestofhealth.Someofthesebeliefsseemto
meonreflectiontobeinconsistentwithsomeothers;Iseethatitisveryunlikelythatall
ofthemcouldbetrue.Perhapstheycouldbe,butIacknowledgethatthereismuchIdo
notunderstand.IfIsitbackandtrytothinkaboutallmy‘knowledge’ofthecommon
cold,then,Imighteasilycometowonderhowmuchofitreallyamountstoknowledge
andhowmuchdoesnot.WhatdoIreallyknowaboutthecommoncold?IfIwere
sufficientlyinterestedinpursuingthematteritwouldbenaturaltolookintothesourceof
mybeliefs.Hasthereeverbeenanygoodreasonforthinkingthatcoldsareeven
correlatedwithwethairincoldweather,forexample,orwithsittinginadraught?Arethe
peoplefromwhomIlearnedsuchthingslikelytohavebelievedthemforgoodreasons?
Arethosebeliefsjustoldwives'tales,oraretheyreallytrue,andperhapsevenknownto
betruebysomepeople?ThesearequestionsImightaskmyself,andIhaveatleasta
generalideaofhowtogoaboutansweringthem.
(p.3) Apartfrommyimpressionoftheimplausibilityofallmybeliefsaboutthecommon
coldbeingtruetogether,Ihavenotmentionedanyotherreasonforbeinginterestedin
investigatingthestateofmyknowledgeonthatsubject.Butforthemomentthatdoesnot
seemtoaffecttheintelligibilityorthefeasibilityofthereflectiveproject.Thereisnothing
mysteriousaboutit.Itisthesortoftaskwecanbeledtoundertakeforanumberof
reasons,andoftenverygoodreasons,insofaraswehaveverygoodreasonsfor
preferringknowledgeandfirmbelieftoguessworkorwishfulthinkingorsimplytaking thingsforgranted.
Reflectiononorinvestigationofourputativeknowledgeneednotalwaysextendtoawide
areaofinterest.Itmightbeimportanttoaskwhethersomequitespecificandparticular
thingIbelieveorhavebeentakingforgrantedisreallysomethingIknow.Asamember
ofajuryImightfindthatIhavebeenrulingoutonesuspectinmymindbecausehewas
athousandmilesaway,inCleveland,atthetimeofthecrime.ButImightthenbeginto
askmyselfwhetherthatisreallysomethingthatIknow.Iwouldreflectonthesourceof
mybelief,butreflectioninthiscaseneednotinvolveageneralscrutinyofeverythingI
takemyselftoknowaboutthecase.Re‐examiningtheman'salibiandthecredentialsofits
supportingwitnessesmightbeenoughtosatisfyme.IndeedImightfindthatitsreliability
onthosecountsispreciselywhatIhadbeengoingonallalong.
Inpointingoutthatweareperfectlyfamiliarwiththeideaofinvestigatingorreviewing
ourknowledgeonsomeparticularmatterorinsomegeneralareaIdonotmeanto
suggestthatitisalwayseasytosettlethequestion.Dependingonthenatureofthecase,
itmightbeverydifficult,perhapsevenimpossibleatthetime,toreachafirmconclusion.
Forexample,itwouldprobablybeverydifficultifnotimpossibleformetotraceand
assesstheoriginsofmanyofthosethingsIbelieveaboutthecommoncold.Butitis
equallytruethatsometimesitisnotimpossibleorevenespeciallydifficulttoanswerthe
question.Wedosometimesdiscoverthatwedonotreallyknowwhatwepreviously Page 3 of 27
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The Problem of the External World
thoughtweknew.ImightfindthatwhatIhadpreviously(p.4) believedisnoteventrue
—thatsittingindraughtsisnotevencorrelatedwithcatchingacold,forexample.OrI
mightfindthatthereisnotorperhapsneverwasanygoodreasontobelievewhatI
believed—thattheman'salibiwasconcoctedandthenfalselytestifiedtobyhisfriends.I
couldreasonablyconcludeineachcasethatI,andeveryoneelseforthatmatter,never
didknowwhatIhadpreviouslythoughtIknew.Weareallfamiliarwiththeordinary
activityofreviewingourknowledge,andwiththeexperienceofreachingapositive
verdictinsomecasesandanegativeverdictinothers.
Descartes'sowninterestinwhatheknowsandhowheknowsitispartofhissearchfor
whathecallsageneralmethodfor‘rightlyconductingreasonandseekingtruthinthe
sciences’.3Hewantsamethodofinquirythathecanbeassuredinadvancewillleadonly
tothetruthifproperlyfollowed.Ithinkwedonotneedtoendorsethewisdomofthat
searchorthefeasibilityofthatprogrammeinordertotrytogoalongwithDescartesin
hisgeneralassessmentofthepositionheisinwithrespecttothethingshebelieves.He
comestofindhisputativeknowledgewantingincertaingeneralrespects,anditisinthe
courseofthatoriginalnegativeassessmentthattheproblemIaminterestedinarises.I
calltheassessment‘negative’becausebytheendofhisFirstMeditationDescartesfinds
thathehasnogoodreasontobelieveanythingabouttheworldaroundhimand
thereforethathecanknownothingoftheexternalworld.
Howisthatassessmentconducted,andhowcloselydoesitparallelthefamiliarkindof
reviewofourknowledgethatweallknowhowtoconductineverydaylife?Thequestion
inoneformoranotherwillbewithusfortherestofthisbook.Itisthequestionofwhat
exactlytheproblemofourknowledgeoftheexternalworldamountsto,andhowitarises
withitsspecialphilosophicalcharacter.Thesourceoftheproblemistobefound
somewherewithinorbehindthekindofthinkingDescartesengagesin.
OnewayDescartes'squestionabouthisknowledgediffersfromtheeverydayexamplesI
consideredisinbeing(p.5) concernedwitheverythinghebelievesortakestobetrue.
Howdoesonegoaboutassessingallofone'sknowledgeallatonce?Iwasabletolista
fewofthethingsIbelieveaboutthecommoncoldandthentoaskabouteachofthem
whetherIreallyknowit,andifsohow.ButalthoughIcancertainlylistanumberofthe
thingsIbelieve,andIwouldassenttomanymoreofthemassoonastheywereputto
me,thereobviouslyisnohopeofassessingeverythingIbelieveinthispiecemealway.
Foronething,itprobablymakesnosense,strictlyspeaking,totalkofthenumberof
thingsonebelieves.IfIamaskedwhetheritisoneofmybeliefsthatIwenttoseeafilm
lastnightIcantrulyanswer‘Yes’.IfIwereaskedwhetheritisoneofmybeliefsthatI
wenttothemovieslastnightIwouldgivethesameanswer.HaveItherebyidentified
two,oronlyone,ofmybeliefs?Howisthatquestionevertobesettled?IfwesaythatI
identifiedonlyoneofmybeliefs,itwouldseemthatImustalsobesaidtoholdthe
furtherbeliefthatgoingtoseeafilmandgoingtothemoviesareoneandthesamething.
Sowewouldhavemorethanonebeliefafterall.Theprospectsofarrivingevenata
principleforcountingbeliefs,letaloneatanactualnumberofthem,seemdim.
Evenifitdidmakesensetocountthethingswebelieveitisprettyclearthatthenumber Page 4 of 27
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The Problem of the External World
wouldbeindefinitelylargeandsoanassessmentofourbeliefsonebyonecouldnever
becompletedanyway.Thisiseasilyseenbyconsideringonlysomeofthesimplestthings
oneknows,forexampleinarithmetic.OnethingIknowisthatoneplusoneequalstwo.
AnotherthingIknowisthatoneplustwoisthree,andanother,thatoneplusthreeis
four.ObviouslytherecouldbenoendtothetaskofassessingmyknowledgeifIhadto
investigateseparatelythesourceofeachoneofmybeliefsinthatseries.AndevenifI
succeededIwouldonlyhaveassessedthethingsIknowabouttheadditionofthe
numberonetoagivennumber;Iwouldstillhavetodothesamefortheadditionoftwo,
andthentheadditionofthree,andsoon.Andeventhatwouldexhaustonlymybeliefs
aboutaddition;allmyothermathematicalbeliefs,nottomentionalltherestofmy
knowledge,wouldremainsofarunexamined.Obviouslythejobcannotbedone
piecemeal,onebyone.(p.6) Somemethodmustbefoundforassessinglargeclassesof beliefsallatonce.
Onewaytodothiswouldbetolookforcommonsourcesorchannelsorbasesofour
beliefs,andthentoexaminethereliabilityofthosesourcesorbases,justasIexamined
thesourceorbasisofmybeliefthatthesuspectwasinCleveland.Descartesdescribes
suchasearchasasearchfor‘principles’ofhumanknowledge,‘principles’whosegeneral
credentialshecantheninvestigate(HR,145).Ifsome‘principles’arefoundtobe
involvedinallorevenmostofourknowledge,anassessmentofthereliabilityofthose
‘principles’couldbeanassessmentofallormostofourknowledge.IfIfoundgood
reasontodoubtthereliabilityofthesuspect'salibi,forexample,andthatwasallIhadto
gooninmybeliefthathewasinCleveland,thenwhatIearliertooktobemyknowledge
thathewasinClevelandwouldhavebeenfoundwantingorcalledintoquestion.Its
sourceorbasiswouldhavebeenundermined.Similarly,ifoneofthe‘principles’orbases
onwhichallmyknowledgeoftheworlddependswerefoundtobeunreliable,my
knowledgeoftheworldwouldtothatextenthavebeenfoundwantingorcalledinto questionaswell.
Arethereanyimportant‘principles’ofhumanknowledgeinDescartes'ssense?Ittakes
verylittlereflectiononthehumanorganismtoconvinceusoftheimportanceofthe
senses—sight,hearing,touch,taste,andsmell.Descartesputsthepointmoststrongly
whenhesaysthat‘allthatuptothepresenttimeIhaveacceptedasmosttrueand
certainIhavelearnedeitherfromthesensesorthroughthesenses’(HR,145).Exactly
whathewouldincludeunder‘thesenses’hereisperhapssomewhatindeterminate,but
evenifitisleftvaguemanyphilosopherswoulddenywhatDescartesappearstobe
saying.Theywouldholdthat,forexample,themathematicalknowledgeImentioned
earlierisnotandcouldnotbeacquiredfromthesensesorthroughthesenses,sonot
everythingIknowisknowninthatway.WhetherDescartesisreallydenyingtheviewsof
thosewhobelieveinthenon‐sensorycharacterofmathematicalknowledge,andwhether,
ifhewere,hewouldberight,areissueswecansetasideforthemoment.Itisclearthat
thesensesareatleast(p.7) veryimportantforhumanknowledge.Evenrestricting
ourselvestothetraditionalfivesenseswecanbegintoappreciatetheirimportanceby
reflectingonhowlittlesomeonewouldevercometoknowwithoutthem.Apersonblind
anddeaffrombirthwhoalsolackedtastebudsandasenseofsmellwouldknowvery Page 5 of 27
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The Problem of the External World
littleaboutanything,nomatterhowlonghelived.Toimaginehimalsoanaesthetizedor
withoutasenseoftouchisperhapstostretchaltogethertoofarone'sconceptionofa
humanorganism,oratleastahumanorganismfromwhomwecanhopetolearn
somethingabouthumanknowledge.Theimportanceofthesensesasasourceorchannel
ofknowledgeseemsundeniable.Itseemspossible,then,toacknowledgetheir
importanceandtoassessthereliabilityofthatsource,quiteindependentlyofthedifficult
questionofwhetherallourknowledgecomestousinthatway.Wewouldthenbe
assessingthecredentialsofwhatisoftencalledour‘sensory’or‘experiential’or
‘empirical’knowledge,andthat,asweshallsee,isquiteenoughtobegoingonwith.
Havingfoundanextremelyimportant‘principle’orsourceofourknowledge,howcanwe
investigateorassessalltheknowledgewegetfromthatsource?Asbefore,wearefaced
withtheproblemoftheinexhaustibilityofthethingswebelieveonthatbasis,sono
piecemeal,one‐by‐oneprocedurewilldo.Butperhapswecanmakeasweepingnegative
assessment.Itmightseemthatassoonaswehavefoundthatthesensesareoneofthe
sourcesofourbeliefsweareimmediatelyinapositiontocondemnallputativeknowledge
derivedfromthem.Somephilosophersappeartohavereasonedinthisway,andmany
haveevensupposedthatDescartesisamongthem.TheideaisthatifIamassessingthe
reliabilityofmybeliefsandaskingwhetherIreallyknowwhatItakemyselftoknow,andI
comeacrossalargeclassofbeliefswhichhavecometomethroughthesenses,Ican
immediatelydismissallthosebeliefsasunreliableorasnotamountingtoknowledge
becauseoftheobviousfactthatIcansometimesbewronginmybeliefsbasedonthe
senses.Thingsarenotalwaysastheyappear,soifonthebasisofthewaytheyappearto
meIbelievethattheyreallyareacertainway,Imightstillbewrong.Wehaveallfoundat
onetimeor(p.8) anotherthatwehavebeenmisledbyappearances;weknowthatthe
sensesarenotalwaysreliable.Shouldwenotconclude,then,thatasageneralsourceof
knowledgethesensesarenottobetrusted?AsDescartesputsit,isitnotwisernever
‘totrustentirelytoanythingbywhichwehaveoncebeendeceived’(HR,145)?Don't
wehavehereaquitegeneralwayofcondemningasnotfullyreliableallofourbeliefs
acquiredbymeansofthesenses?
Ithinktheanswertothatquestionis‘No,wedonot’,andIthinkDescarteswouldagree
withthatanswer.Itistruethathedoestalkofthesenses‘deceiving’usonparticular
occasions,andhedoesaskwhetherthatisnotenoughtocondemnthesensesingeneral
asasourceofknowledge,butheimmediatelyremindsusoftheobviousfactthatthe
circumstancesinwhichthesenses‘deceive’usmightbespecialincertainascertainable
ways,andsotheiroccasionalfailureswouldnotsupportablanketcondemnationoftheir reliability.
Sometimes,togiveanancientexample,atowerlooksroundfromadistancewhenitis
actuallysquare.Ifwereliedonlyontheappearancesofthemomentwemightsaythatthe
distanttowerisround,andwewouldbewrong.Wealsoknowthattherearemanysmall
organismsinvisibletothenakedeye.Ifthetablebeforemeiscoveredwithsuch
organismsatthemomentbutIlookatitandsaythereisnothingonthetableatall,once
againIwillbewrong.Butallthatfollowsfromthesefamiliarfacts,asDescartespointsout, Page 6 of 27
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The Problem of the External World
isthattherearethingsaboutwhichwecanbewrong,ortherearesituationsinwhichwe
cangetfalsebeliefs,ifwerelyentirelyonoursensesatthatmoment.Sosometimeswe
shouldbecarefulaboutwhatwebelieveonthebasisofthesenses,orsometimes
perhapsweshouldwithholdourassentfromanystatementabouthowthingsare—when
thingsaretoofarawaytobeseenproperly,forexample,ortoosmalltobeseenatall.
Butthatobviouslyisnotenoughtosupportthepolicyofnevertrustingone'ssenses,or
neverbelievinganythingbasedonthem.NordoesitshowthatIcanneverknow
anythingbymeansofthesenses.Ifmycarstartspromptlyeverymorningfortwoyears
intemperateweatheratsealevelbutthenfailstostart(p.9) onemorninginfreez ing
weatheratthetopofahighmountain,thatdoesnotsupportthepolicyofnevertrusting
mycartostartagainonceIreturntothetemperateloweraltitudefromwhichIso
foolishlytookit.NordoesitshowthatIcanneverknowwhethermycarwilleverstart
again.Itshowsonlythattherearecertaincircumstancesinwhichmyotherwisefully
reliablecarmightnotstart.Sothefactthatwearesometimeswrongor‘deceived’inour
judgementsbasedonthesensesisnotenoughinitselftoshowthatthesensesarenever
tobetrustedandarethereforeneverreliableasasourceofknowledge.
Descartes'snegativeassessmentofallofhissensoryknowledgedoesnotdependonany
suchreasoning.Hestartshisinvestigation,rather,inwhatwouldseemtobethemost
favourableconditionsforthereliableoperationofthesensesasasourceofknowledge.
WhileengagingintheveryphilosophicalreflectionsheiswritingaboutinhisFirst
MeditationDescartesissittinginawarmroom,bythefire,inadressinggown,witha
pieceofpaperinhishand.Hefindsthatalthoughhemightbeabletodoubtthatadistant
towerthatlooksroundreallyisround,itseemsimpossibletodoubtthathereallyis
sittingtherebythefireinhisdressinggownwithapieceofpaperinhishand.Thefireand
thepieceofpaperarenottoosmallortoofarawaytobeseenproperly,theyareright
therebeforehiseyes;itseemstobethebestkindofpositionsomeonecouldbeinfor
gettingreliablebeliefsorknowledgebymeansofthesensesaboutwhatisgoingon
aroundhim.ThatisjusthowDescartesregardsit.Itsbeingabest‐possiblecaseofthat
kindispreciselywhathethinksenableshimtoinvestigateorassessatonefellswoopall
oursensoryknowledgeoftheworldaroundus.Theverdicthearrivesatabouthis
putativeknowledgethatheissittingbythefirewithapieceofpaperinhishandinthat
particularsituationservesasthebasisforacompletelygeneralassessmentofthesenses
asasourceofknowledgeabouttheworldaroundus.
Howcanthatbeso?Howcanhesoeasilyreachageneralverdictaboutallhissensory
knowledgeonthebasisofasingleexample?Obviouslynotsimplybygeneraliz ingfrom
oneparticularexampletoallcasesofsensoryknowledge,asonemightwildlyleaptoa
conclusionaboutallred‐haired(p.10) menonthebasisofoneortwoindividuals.
Rather,hetakestheparticularexampleofhisconvictionthatheissittingbythefirewitha
pieceofpaperinhishandasrepresentativeofthebestpositionanyofuscaneverbein
forknowingthingsabouttheworldaroundusonthebasisofthesenses.Whatistrueof
arepresentativecase,ifitistrulyrepresentativeanddoesnotdependonspecial
peculiaritiesofitsown,canlegitimatelysupportageneralconclusion.Ademonstration
thataparticularisoscelestrianglehasacertainproperty,forexample,canbetakenasa Page 7 of 27
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The Problem of the External World
demonstrationthatallisoscelestriangleshavethatproperty,aslongastheoriginal
instancewastypicalorrepresentativeofthewholeclass.WhetherDescartes's
investigationofthegeneralreliabilityofthesensesreallydoesfollowthatfamiliarpattern
isadifficultquestion.Whether,orinpreciselywhatsense,theexampleheconsiderscan
betreatedasrepresentativeofourrelationtotheworldaroundusis,Ibelieve,thekey
tounderstandingtheproblemofourknowledgeoftheexternalworld.Butifitturnsout
thatthereisnothingillegitimateaboutthewayhisnegativeconclusionisreached,the
problemwillbeproperlyposed.
ForthemomentIthinkatleastthismuchcanbesaidaboutDescartes'sreasoning.He
choosesthesituationinwhichhefindshimselfasrepresentativeofthebestpositionwe
canbeinforknowingthingsabouttheworldinthesensethat,ifitisimpossibleforhimin
thatpositiontoknowthatheissittingbythefirewithapieceofpaperinhishandthenitis
alsoimpossibleforhiminothersituationstoknowanythingabouttheworldaroundhim
onthebasisofhissenses.Anegativeverdictinthechosencasewouldsupportanegative
verdicteverywhereelse.TheexampleDescartesconsidersisinthatsensemeanttobe
thebestkindofcasetherecouldbeofsensoryknowledgeabouttheworldaroundus.I
thinkwemustadmitthatitisverydifficulttoseehowDescartesoranyoneelsecouldbe
anybetteroffwithrespecttoknowingsomethingabouttheworldaroundhimonthe
basisofthesensesthanheisinthecaseheconsiders.Butifnoonecouldbeinany
betterpositionforknowing,itseemsnaturaltoconcludethatanynegativeverdict
arrivedataboutthisexample,anydiscoverythatDescartes'sbeliefsinthiscasearenot
reliableordonotamounttoknowledge,could(p.11) safelybegeneraliz edintoa
negativeconclusionaboutallofoursensory‘knowledge’oftheworld.Ifcandidateswith
thebestpossiblecredentialsarefoundwanting,allthosewithlessimpressivecredentials
mustfallshortaswell.
Itwillseematfirstsightthatinconcedingthatthewholequestionturnsonwhether
Descartesknowsinthisparticularcaseweareconcedingverylittle;itseemsobvious
thatDescartesonthatoccasiondoesknowwhathethinksheknowsabouttheworld
aroundhim.ButinfactDescartesfindsthathecannotknowinthiscasethatheissitting
bythefirewithapieceofpaperinhishand.Ifthecaseistrulyrepresentativeofour
sensoryknowledgeingeneral,thatwillshowthatnoonecanknowanythingaboutthe
worldaroundus.Buthowcouldheeverarriveatthatnegativeverdictintheparticular
caseheconsiders?Howcouldanyonepossiblydoubtinsuchacasethatthefireandthe
pieceofpaperarethere?ThepaperisinDescartes'shand,thefireisrighttherebefore
hisopeneyes,andhefeelsitswarmth.Wouldn'tanyonehavetobemadtodenythathe
canknowsomethingaboutwhatisgoingonaroundhiminthosecircumstances?
Descartesfirstanswers‘Yes’.Hesaysthatifheweretodoubtordenyonthatoccasion
thatheissittingbythefirewithapieceofpaperinhishandhewouldbenolessmadthan
thosepauperswhosaytheyarekingsorthosemadmenwhothinktheyarepumpkinsor
aremadeofglass.Buthisreflectionscontinue:
AtthesametimeImustrememberthatIamaman,andthatconsequentlyIamin
thehabitofsleeping,andinmydreamsrepresentingtomyselfthesamethingsor Page 8 of 27
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The Problem of the External World
sometimesevenlessprobablethings,thandothosewhoareinsaneintheirwaking
moments.HowoftenhasithappenedtomethatinthenightIdreamtthatIfound
myselfinthisparticularplace,thatIwasdressedandseatednearthefire,whilstin
realityIwaslyingundressedinbed!Atthismomentitdoesindeedseemtome
thatitiswitheyesawakethatIamlookingatthispaper;thatthisheadwhichImove
isnotasleep,thatitisdeliberatelyandofsetpurposethatIextendmyhandand
perceiveit;whathappensinsleepdoesnotappearsoclearnorsodistinctasdoes
allthis.ButinthinkingoverthisIremindmyselfthatonmanyoccasionsIhavein
sleepbeendeceivedbysimilarillusions,andindwellingcarefullyonthisreflectionI
seesomanifestlythattherearenocertainindicationsbywhichwemayclearly
distinguishwakefulnessfromsleepthatIamlostinastonishment.Andmy
astonishmentissuchthatitisalmostcapableofpersuadingmethatInowdream. (HR,145–6.)
(p.12) Withthisthought,ifheisright,Descarteshaslostthewholeworld.Heknows
whatheisexperiencing,heknowshowthingsappeartohim,buthedoesnotknow
whetherheisinfactsittingbythefirewithapieceofpaperinhishand.Itis,forhim,
exactlyasifheweresittingbythefirewithapieceofpaperinhishand,buthedoesnot
knowwhethertherereallyisafireorapieceofpaperthereornot;hedoesnotknow
whatisreallyhappeningintheworldaroundhim.Herealiz esthatifeverythinghecan
everlearnaboutwhatishappeningintheworldaroundhimcomestohimthroughthe
senses,buthecannottellbymeansofthesenseswhetherornotheisdreaming,thenall
thesensoryexperiencesheishavingarecompatiblewithhismerelydreamingofaworld
aroundhimwhileinfactthatworldisverydifferentfromthewayhetakesittobe.Thatis
whyhethinkshemustfindsomewaytotellthatheisnotdreaming.Farfromitsbeing
madtodenythatheknowsinthiscase,hethinkshisrecognitionofthepossibilitythathe
mightbedreaminggiveshim‘verypowerfulandmaturelyconsidered’(HR,148)
reasonsforwithholdinghisjudgementabouthowthingsareintheworldaroundhim.He
thinksitiseminentlyreasonabletoinsistthatifheistoknowthatheissittingbythefire
hemustknowthatheisnotdreamingthatheissittingbythefire.Thatisseenasa
necessaryconditionofknowingsomethingabouttheworldaroundhim.Andhefindsthat
thatconditioncannotbefulfilled.Oncarefulreflectionhediscoversthat‘thereareno
certainindicationsbywhichwemayclearlydistinguishwakefulnessfromsleep’.He
concludesthatheknowsnothingabouttheworldaroundhimbecausehecannottellthat
heisnotdreaming;hecannotfulfiloneoftheconditionsnecessaryforknowingsomething abouttheworld.
TheCartesianproblemofourknowledgeoftheexternalworldthereforebecomes:how
canweknowanythingabouttheworldaroundusonthebasisofthesensesifthesenses
giveusonlywhatDescartessaystheygiveus?Whatwegainthroughthesensesison
Descartes'sviewonlyinformationthatiscompatiblewithourdreamingthingsaboutthe
worldaroundusandnotknowinganythingaboutthatworld.Howthencanweknow
anythingabouttheworldbymeansofthe(p.13) senses?TheCartesianargument
presentsachallengetoourknowledge,andtheproblemofourknowledgeoftheexternal
worldistoshowhowthatchallengecanbemet. Page 9 of 27
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The Problem of the External World
WhenIspeakhereoftheCartesianargumentorofDescartes'sscepticalconclusionorof
hisnegativeverdictabouthisknowledgeIreferofcourseonlytothepositionhefinds
himselfinbytheendofhisFirstMeditation.Havingatthatpointdiscoveredandstated
theproblemoftheexternalworld,DescartesgoesonintherestofhisMeditationstotry
tosolveit,andbytheendoftheSixthMeditationhethinkshehasexplainedhowhe
knowsalmostallthosefamiliarthingshebeganbyputtinginquestion.SowhenIascribe
toDescartestheviewthatwecanknownothingabouttheworldaroundusIdonot
meantosuggestthatthatishisfinalandconsideredview;itisnothingmorethana
conclusionhefeelsalmostinevitablydriventoattheearlystagesofhisreflections.But
thosearetheonlystagesofhisthinkingIaminterestedinhere.Thatiswherethe
philosophicalproblemofourknowledgeoftheexternalworldgetsposed,andbeforewe
canconsiderpossiblesolutionswemustbesureweunderstandexactlywhatthe problemis.
Ihavedescribeditasthatofshowingorexplaininghowknowledgeoftheworldaround
usispossiblebymeansofthesenses.Itisimportanttokeepinmindthatthatdemandfor
anexplanationarisesinthefaceofachallengeorapparentobstacletoourknowledgeof
theworld.ThepossibilitythatheisdreamingisseenasanobstacletoDescartes's
knowingthatheissittingbythefire,anditmustbeexplainedhowthatobstaclecaneither
beavoidedorovercome.Itmustbeshownorexplainedhowitispossibleforustoknow
thingsabouttheworld,giventhatthesense‐experienceswegetarecompatiblewithour
merelydreaming.Explaininghowsomethingisneverthelesspossible,despitewhatlooks
likeanobstacletoit,requiresmorethanshowingmerelythatthereisnoimpossibility
involvedinthething—thatitisconsistentwiththeprinciplesoflogicandthelawsofnature
andsointhatsensecouldexist.Themerepossibilityofthestateofaffairsisnotenoughto
settlethequestionofhowourknowledgeoftheworldispossible;wemustunderstand
howtheapparentobstacleistobegotround.
(p.14) Descartes'sreasoningcanbeexaminedandcriticizedatmanydifferentpoints,
andhasbeencloselyscrutinizedbymanyphilosophersforcenturies.Ithasalsobeen
acceptedbymany,perhapsbymorethanwouldadmitorevenrealiz ethattheyacceptit.
Thereseemstomenodoubtabouttheforceandthefascination—Iwouldsaythealmost
overwhelmingpersuasiveness—ofhisreflections.Thataloneissomethingthatneeds
accountingfor.Icannotpossiblydojusticetoallreasonablereactionstothemhere.In
therestofthisfirstchapterIwanttoconcentrateondeepeningandstrengtheningthe
problemandtryingtolocatemorepreciselythesourceofitspower.
Thereareatleastthreedistinctquestionsthatcouldbepressed.Isthepossibilitythat
Descartesmightbedreamingreallyathreattohisknowledgeoftheworldaroundhim?
Isherightinthinkingthathemustknowthatheisnotdreamingifheistoknow
somethingabouttheworldaroundhim?Andisherightinhis‘discovery’thathecan
neverknowthatheisnotdreaming?IfDescarteswerewrongonanyofthesepointsit
mightbepossibletoavoidtheproblemandperhapseventoexplainwithoutdifficultyhow
weknowthingsabouttheworldaroundus.
Onthefirstquestion,itcertainlyseemsrighttosaythatifDescartesweredreamingthat Page 10 of 27
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The Problem of the External World
heissittingbythefirewithapieceofpaperinhishandhewouldnotthenknowthatheis
sittingbythefirewithapieceofpaperinhishand.Whenyoudreamthatsomethingis
goingonintheworldaroundyouyoudonottherebyknowthatitis.Mostoften,of
course,whatwedreamisnoteventrue;nooneisactuallychasinguswhenwearelying
asleepinbeddreaming,norareweactuallyclimbingstairs.Butalthoughusuallywhatwe
dreamisnotreallyso,thatisnottherealreasonforourlackofknowledge.Evenif
Descarteswereinfactsittingbythefireandactuallyhadapieceofpaperinhishandat
theverytimehewasdreamingthatheissittingbythefirewithapieceofpaperinhis
hand,hewouldnottherebyknowhewassittingtherewiththatpaper.Hewouldbelikea
certainDukeofDevonshirewho,accordingtoG.E.Moore,oncedreamthewasspeaking
intheHouseofLordsandwokeuptofindthathewasspeakingintheHouseof(p.15)
Lords.4Whathewasdreamingwasinfactso.Butevenifwhatyouaredreamingisinfact
soyoudonottherebyknowthatitis.Evenifweallowthatwhenyouaredreamingthat
somethingissoyoucanbesaid,atleastforthetimebeing,tothinkortobelievethatitis
so,thereisstillnorealconnectionbetweenyourthinkingorbelievingwhatyoudoandits
beingso.Atbestyouhaveathoughtorabeliefwhichjusthappenstobetrue,butthatis
nomorethancoincidenceandnotknowledge.SoDescartes'sfirststepreliesonwhat
seemstobeanundeniablefactaboutdreams:ifyouaredreamingthatsomethingisso
youdonottherebyknowthatitisso.
Thisbaldclaimneedstobequalifiedandmorecarefullyexplained,butIdonotthinkthat
willdiminishtheforceofthepointforDescartes'spurposes.Sometimeswhatisgoingon
intheworldaroundushasaneffectonwhatwedream;forexample,abangingshutter
mightactuallycausemetodream,amongotherthings,thatashutterisbanging.Ifmy
environmentaffectsmeinthatway,andifindreamsIcanbesaidtothinkorbelievethat
somethingisso,wouldInotinthatcaseknowthatashutterisbanging?Itseemstome
thatIwouldnot,butIconfessitisdifficulttosayexactlywhyIthinkso.Thatisprobably
becauseitisdifficulttosayexactlywhatisrequiredforknowledge.Weusetheterm
‘know’confidently,wequiteeasilydistinguishcasesofknowledgefromcasesofits
absence,butwearenotalwaysinapositiontostatewhatwearegoingoninapplyingor
withholdingtheterminthewayswedo.Ithinkthatinthecaseofthebangingshutterit
wouldnotbeknowledgebecauseIwouldbedreaming,Iwouldnotevenbeawake.At
leastitcanbesaid,Ithink,thatevenifDescartes'ssittingbythefirewithapieceofpaper
inhishand(likethebangingshutter)iswhatinfactcauseshimtodreamthatheissitting
bythefirewithapieceofpaperinhishand,thatisstillnohelptohimincomingtoknow
whatisgoingonintheworldaroundhim.Herealiz esthathecouldbedreamingthathe
issittingbythefireevenifheisinfactsittingthere,andthatisthepossibilityhefindshe hastoruleout.
Ihavesaidthatifyouaredreamingthatsomethingisso(p.16) youdonotthereby
knowthatitisso,anditmightseemasifthatisnotalwaystrue.Supposeamananda
childarebothsleeping.Isayofthechildthatitissoyoungitdoesnotknowwhatseven
timesnineis,whereasthegrownmandoesknowthat.Ifthemanhappensatthatvery
momenttobedreamingthatseventimesnineissixty‐three(perhapsheisdreamingthat
heiscomputinghisincometax),thenheisamanwhoisdreamingthatsomethingisso Page 11 of 27
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The Problem of the External World
andalsoknowsthatitisso.Thesamekindofthingispossibleforknowledgeaboutthe
worldaroundhim.Hemightbeaphysicistwhoknowsagreatdealaboutthewaythings
arewhichthechilddoesnotknow.Ifthemanalsodreamsthatthingsarethatwayhecan
onceagainbesaidtobedreamingthatsomethingissoandalsotoknowthatitisso.
Thereisthereforenoincompatibilitybetweendreamingandknowing.Thatistrue,butI
donotthinkitaffectsDescartes'sargument.Heisledtoconsiderhowheknowsheisnot
dreamingatthemomentbyreflectingonhowheknowsatthatmomentthatheissitting
bythefirewithapieceofpaperinhishand.Ifheknowsthatatall,hethinks,heknowsit
onthebasisofthesenses.Butherealiz esthathishavingthesensoryexperiencesheis
nowhavingiscompatiblewithhismerelydreamingthatheissittingbythefirewitha
pieceofpaperinhishand.Sohedoesnotknowonthebasisofthesensoryexperiences
heishavingatthemomentthatheissittingbythefire.Nor,ofcourse,didthemaninmy
examplesknowthethingshewassaidtoknowonthebasisofthesensoryexperienceshe
washavingatthatmoment.Heknewcertainthingstobeso,andhewasdreamingthose
thingstobeso,butindreamingthemhedidnottherebyknowthemtobeso.
Butaslongasweallowthatthesleepingmandoesknowcertainthingsabouttheworld
aroundhim,evenifhedoesnotknowthemonthebasisoftheverydreamsheishaving
atthemoment,isn'tthatenoughtoshowthatDescartesmustneverthelessbewrongin
hisconclusionthatnoonecanknowanythingabouttheworldaroundhim?No.Itshows
atmostthatwewerehastyorwereignoringDescartes'sconclusioninconcedingthat
someonecouldknowsomethingabouttheworldaroundhim.IfDescartes'sreasoningis
correctthedreamingphysicist,evenwhenheisawake,does(p.17) notreallyknowany
ofthethingswewereuncriticallycreditinghimwithknowingaboutthewaythingsare—
oratleasthedoesnotknowthemonthebasisofthesenses.Inordertoknowthemon
thebasisofthesensestherewouldhavetohavebeenatleastsometimeatwhichhe
knewsomethingaboutwhatwasgoingonaroundhimatthattime.ButifDescartesis
righthecouldnothaveknownanysuchthingunlesshehadestablishedthathewasnot
dreamingatthattime;andaccordingtoDescarteshecouldneverestablishthat.Sothe
factaboutdreamsthatDescartesrelieson—thatonewhodreamsthatsomethingisso
doesnottherebyknowthatitisso—isenoughtoyieldhisconclusioniftheotherstepsof
hisreasoningarecorrect.
WhenhefirstintroducesthepossibilitythathemightbedreamingDescartesseemstobe
relyingonsomeknowledgeabouthowthingsareorwereintheworldaroundhim.He
says‘IremindmyselfthatonmanyoccasionsIhaveinsleepbeendeceivedbysimilar
illusions’,soheseemstoberelyingonsomeknowledgetotheeffectthathehasactually
dreamtinthepastandthatheremembershavingbeen‘deceived’bythosedreams.That
ismorethanheactuallyneedsforhisreflectionsaboutknowledgetohavetheforcehe
thinkstheyhave.Hedoesnotneedtosupporthisjudgementthathehasactuallydreamt
inthepast.Theonlythoughtheneedsisthatitisnowpossibleforhimtobedreaming
thatheissittingbythefire,andthatifthatpossibilitywererealiz edhewouldnotknow
thatheissittingbythefire.OfcourseitwasnodoubttruethatDescarteshaddreamtin
thepastandthathisknowledgethathehaddonesowaspartlywhathewasgoingonin
acknowledgingthepossibilityofhisdreamingonthisparticularoccasion.Butneitherthe Page 12 of 27
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factofpastdreamsnorknowledgeoftheiractualoccurrencewouldseemtobestrictly
requiredinordertograntwhatDescartesrelieson—thepossibilityofdreaming,andthe
absenceofknowledgeifthatpossibilitywererealiz ed.Thethoughtthathemightbe
dreamingthatheissittingbythefirewithapieceofpaperinhishand,andthefactthatif
hewerehewouldn'tknowhewassittingthere,iswhatgivesDescartespause.That
wouldworryhiminthewayitdoesevenifhehadneveractuallyhadanydreamsexactly
likeit(p.18) inthepast—ifhehadneverdreamtaboutfiresandpiecesofpaperatall.In
fact,Ithinkheneedneverhaveactuallydreamtofanythingbefore,andcertainlyneedn't
knowthatheeverhas,inordertobeworriedinthewayheisbythethoughtthathe mightbedreamingnow.
ThefactthatthepossibilityofdreamingisallDescartesneedstoappealtobringsout
anothertruthaboutdreamsthathisargumentdependson—thatanythingthatcanbe
goingonorthatonecanexperienceinone'swakinglifecanalsobedreamtabout.This
againisonlyastatementofpossibility—nosensiblepersonwouldsuggestthatwedoat
sometimedreamofeverythingthatactuallyhappenstous,orthateverythingwedream
aboutdoesinfacthappensometime.Butitisveryplausibletosaythatthereisnothing
wecouldnotdreamabout,nothingthatcouldbethecasethatwecouldnotdreamtobe
thecase.Isayitisveryplausible;ofcourseIcannotproveittobetrue.Butevenifitis
nottruewithcompletegenerality,wemustsurelygrantthatitispossibletodreamthat
oneissittingbyafirewithapieceofpaperinone'shand,andpossibletodreamof
countlessotherequallyobviousandequallymundanestatesofaffairsaswell,andthose
possibilitiesarewhatDescartesseesasthreateningtohisknowledgeoftheworldaround him.
Thereseemslittlehope,then,ofobjectingthatitissimplynotpossibleforDescartesto
dreamthatheissittingbythefirewithapieceofpaperinhishand.Norisitanymore
promisingtosaythatevenifheweredreamingitwouldnotfollowthathedidnotknow
thathewassittingthere.IthinkboththosestepsorassumptionsofDescartes's
reasoningareperfectlycorrect,andfurtherdefenceofthematthisstageisunnecessary.
Ifhisargumentandtheproblemtowhichitgivesrisearetobeavoided,itmightseem
thatthebesthopeisthereforetoaccepthischallengeandshowthatitcanbemet.That
wouldbeineffecttoarguethatDescartes'salleged‘discovery’isnodiscoveryatall:we
cansometimesknowthatwearenotdreaming.
Thiscaneasilyseemtobethemoststraightforwardandmostpromisingstrategy.It
allowsthatDescartesisrightinthinkingthatknowingthatoneisnotdreamingisa
condition(p.19) ofknowingsomethingabouttheworldaroundus,butwronginthinking
thatthatconditioncanneverbemet.Andthatcertainlyseemsplausible.Surelyitisnot
impossibleformetoknowthatIamnotdreaming?Isn'tthatsomethingIoftenknow,and
isn'titsomethingIcansometimesfindoutifthequestionarises?Ifitis,thenthefactthat
ImustknowthatIamnotdreamingifIamtoknowanythingabouttheworldaroundme
willbenothreattomyknowledgeoftheworld.
Howeverobviousandundeniableitmightbethatweoftendoknowthatwearenot
dreaming,IthinkthisstraightforwardresponsetoDescartes'schallengeisatotalfailure. Page 13 of 27
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IncallingitstraightforwardImeanthatitacceptsDescartes'sconditionsforknowledgeof
theworldandtriestoshowthattheycanbefulfilled.ThatiswhatIthinkcannotbedone.
Toputthesamepointinanotherway:IthinkDescarteswouldbeperfectlycorrectin
saying‘therearenocertainindicationsbywhichwemayclearlydistinguishwakefulness
fromsleep’,andsowecouldnevertellwearenotdreaming,ifhewerealsorightthat
knowingthatoneisnotdreamingisaconditionofknowingsomethingabouttheworld
aroundus.ThatiswhyIthinkonecannotacceptthatconditionandthengoontoestablish
thatoneisnotdreaming.IdonotmeantobesayingsimplythatDescartesisright—that
wecanneverknowthatwearenotdreaming.ButIdowanttoarguethateitherwecan
neverknowthatwearenotdreamingorelsewhatDescartessaysisaconditionof
knowingthingsabouttheworldisnotreallyaconditioningeneralofknowingthingsabout
theworld.Thestraightforwardstrategydeniesbothalternatives.Iwilltrytoexplainwhy
Ithinkwemustacceptonealternativeortheother.
WhenDescartesaskshimselfhowheknowsthatheissittingbythefirewithapieceof
paperinhishandwhydoesheimmediatelygoontoaskhimselfhowheknowsheisnot
dreamingthatheissittingbythefirewithapieceofpaperinhishand?Ihavesuggested
thatitisbecauseherecognizesthatifheweredreaminghewouldnotknowonthebasis
ofhissensesatthemomentthatheissittingthere,andsohethinkshemustknowthat
thatpossibilitydoesnotobtainifheistoknowthatheisinfactsittingthere.(p.20) But
thisparticularexamplewaschosen,notforanypeculiaritiesitmightbethoughtto
possess,butbecauseitcouldbetakenastypicalofthebestpositionwecaneverbein
forcomingtoknowthingsabouttheworldaroundusonthebasisofthesenses.Whatis
trueofthiscasethatisrelevanttoDescartes'sinvestigationofknowledgeissupposedto
betrueofallcasesofknowledgeoftheworldbymeansofthesenses;thatiswhythe
verdictarrivedatherecanbetakentobetrueofoursensoryknowledgegenerally.But
whatDescartesthinksistrueofthisparticularcaseofsensoryknowledgeoftheworldis
thathemustknowheisnotdreamingifheistoknowthatheissittingbythefirewitha
pieceofpaperinhishand.Thatisrequired,notbecauseofanypeculiaritiesofthis
particularcase,butpresumablybecause,accordingtoDescartes,itisanecessary
conditionofanycase—evenabestpossiblecase—ofknowledgeoftheworldbymeansof
thesenses.ThatiswhyIascribedtoDescartesthequitegeneralthesisthatknowingthat
oneisnotdreamingisaconditionofknowingsomethingabouttheworldarounduson
thebasisofthesenses.Sincehethinksthepossibilityofhisdreamingmustberuledout
inthecaseheconsiders,andthecaseheconsidersisregardedastypicalandwithout
specialcharacteristicsofitsown,hethinksthatthepossibilitythatheisdreamingmustbe
ruledoutineverycaseofknowingsomethingabouttheworldbymeansofthesenses.
Ifthatreallyisaconditionofknowingsomethingabouttheworld,Ithinkitcanbeshown
thatDescartesisrightinholdingthatitcanneverbefulfilled.Thatiswhatthe
straightforwardresponsedenies,andthatiswhyIthinkthatresponsemustbewrong.
WecannotacceptthetermsofDescartes'schallengeandthenhopetomeetit.
SupposeDescartestriestodeterminethatheisnotdreaminginordertofulfilwhathe
seesasanecessaryconditionofknowingthatheissittingbythefirewithapieceofpaper Page 14 of 27
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The Problem of the External World
inhishand.Howishetoproceed?Herealiz esthathisseeinghishandandseeingand
feelingapieceofpaperbeforehimandfeelingthewarmthofthefire—infacthisgettingall
thesensoryexperiencesorallthesensoryinformationheisthengetting—issomething
thatcouldbehappeningeven(p.21) ifheweredreaming.Toestablishthatheisnot
dreaminghewouldthereforeneedsomethingmorethanjustthoseexperiencesorthat
informationalone.Hewouldalsoneedtoknowwhetherthoseexperiencesandthat
informationarereliable,notmerelydreamt.Ifhecouldfindsomeoperationortest,orif
hecouldfindsomecircumstanceorstateofaffairs,thatindicatedtohimthathewasnot
dreaming,perhapshecouldthenfulfilthecondition—hecouldknowthathewasnot
dreaming.Buthowcouldatestoracircumstanceorastateofaffairsindicatetohimthat
heisnotdreamingifaconditionofknowinganythingabouttheworldisthatheknowheis
notdreaming?Itcouldnot.Hecouldneverfulfilthecondition.
Letussupposethatthereisinfactsometestwhichapersoncanperformsuccessfully
onlyifheisnotdreaming,orsomecircumstanceorstateofaffairswhichobtainsonlyif
thatpersonisnotdreaming.Ofcourseforthattestorstateofaffairstobeofanyuseto
himDescarteswouldhavetoknowofit.Hewouldhavetoknowthatthereissuchatest
orthatthereisastateofaffairsthatshowsthatheisnotdreaming;withoutsuch
informationhewouldbenobetterofffortellingthatheisnotdreamingthanhewouldbe
iftherewerenosuchtestorstateofaffairsatall.Tohaveacquiredthatinformationhe
wouldatsometimehavetohaveknownmorethanjustsomethingaboutthecourseof
hissensoryexperience,sincetheconnectionbetweentheperformanceofacertaintest,
orbetweenacertainstateofaffairs,andsomeone'snotdreamingisnotitselfjustafact
aboutthecourseofthatperson'ssensoryexperience;itisafactabouttheworldbeyond
hissensoryexperiences.Nowstrictlyspeakingifitisaconditionofknowinganything
abouttheworldbeyondone'ssensoryexperiencesthatoneknowthatoneisnot
dreaming,thereisanobviousobstacletoDescartes'severhavinggottheinformationhe
needsaboutthattestorstateofaffairs.Hewouldhavetohaveknownatsometimethat
hewasnotdreaminginordertogettheinformationheneedstotellatanytimethatheis
notdreaming—andthatcannotbedone.
ButsupposeweforgetaboutthisdifficultyandconcedethatDescartesdoesindeed
know(somehow)thatthereis(p.22) atestorcircumstanceorstateofaffairsthat
unfailinglyindicatesthatheisnotdreaming.Still,thereisanobstacletohiseverusingthat
testorstateofaffairstotellthatheisnotdreamingandtherebyfulfillingtheconditionfor
knowledgeoftheworld.Thetestwouldhavetobesomethinghecouldknowhehad
performedsuccessfully,thestateofaffairswouldhavetobesomethinghecouldknow
obtains.Ifhecompletelyunwittinglyhappenedtoperformthetest,orifthestateofaffairs
happenedtoobtainbuthedidn'tknowthatitdid,hewouldbeinnobetterpositionfor
tellingwhetherhewasdreamingthanhewouldbeifhehaddonenothingordidnoteven
knowthattherewassuchatest.Buthowishetoknowthatthetesthasbeenperformed
successfullyorthatthestateofaffairsinquestiondoesinfactobtain?Anythingonecan
experienceinone'swakinglifecanalsobedreamtabout;itispossibletodreamthatone
hasperformedacertaintestordreamthatonehasestablishedthatacertainstateof
affairsobtains.And,aswehaveseen,todreamthatsomethingabouttheworldaround Page 15 of 27
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The Problem of the External World
youissoisnottherebytoknowthatitisso.Inordertoknowthathistesthasbeen
performedorthatthestateofaffairsinquestionobtainsDescarteswouldthereforehave
toestablishthatheisnotmerelydreamingthatheperformedthetestsuccessfullyor
thatheestablishedthatthestateofaffairsobtains.Howcouldthatinturnbeknown?
Obviouslytheparticulartestorstateofaffairsalreadyinquestioncannotserveasa
guaranteeofitsownauthenticity,sinceitmighthavebeenmerelydreamt,sosome
furthertestorstateofaffairswouldbeneededtoindicatethattheoriginaltestwas
actuallyperformedandnotmerelydreamt,orthatthestateofaffairsinquestionwas
actuallyascertainedtoobtainandnotjustdreamttoobtain.Butthisfurthertestorstate
ofaffairsissubjecttothesamegeneralconditioninturn.Everypieceofknowledgethat
goesbeyondone'ssensoryexperiencesrequiresthatoneknowoneisnotdreaming.
ThissecondtestorstateofaffairswillthereforebeofuseonlyifDescartesknowsthathe
isnotmerelydreamingthatheisperformingorascertainingit,sincemerelytodream
thathehadestablishedtheauthenticityofthefirsttestisnottohaveestablishedit.And
soon.Atnopointcanhefindatestfor(p.23) notdreamingwhichhecanknowhasbeen
successfullyperformedorastateofaffairscorrelatedwithnotdreamingwhichhecan
knowobtains.HecanthereforeneverfulfilwhatDescartessaysisanecessarycondition
ofknowingsomethingabouttheworldaroundhim.Hecanneverknowthatheisnot dreaming.
Imustemphasiz ethatthisconclusionisreachedonlyontheassumptionthatitisa
conditionofknowinganythingabouttheworldaroundusonthebasisofthesensesthat
weknowwearenotdreamingthatthethingisso.Ithinkitishisacceptanceofthat
conditionthatleadsDescartesto‘seesomanifestlythattherearenocertainindications
bywhichwemayclearlydistinguishwakefulnessfromsleep’.AndIthinkDescartesis
absolutelyrighttodrawthatconclusion,givenwhathethinksisaconditionofknowledge
oftheworld.ButallIhavearguedonDescartes'sbehalf(heneverspellsouthis
reasoning)isthatwecannotbothacceptthatconditionofknowledgeandhopetofulfilit,
asthestraightforwardresponsehopestodo.Andofcourseifoneofthenecessary
conditionsofknowledgeoftheworldcanneverbefulfilled,knowledgeoftheworld
arounduswillbeimpossible.
IthinkwehavenowlocatedDescartes'sreasonforhisnegativeverdictaboutsensory
knowledgeingeneral.Ifweagreethathemustknowthatheisnotdreamingifheisto
knowinhisparticularcasethatheissittingbythefirewithapieceofpaperinhishand,
wemustalsoagreethatwecanknownothingabouttheworldaroundus.
Oncewerecogniz ethattheconditionDescartestakesasnecessarycanneverbefulfilled
ifheisrightinthinkingitisindeednecessary,wearenaturallyledtothequestion
whetherDescartesisright.Isitreallyaconditionofknowingsomethingabouttheworld
thatoneknowoneisnotdreaming?ThatisthesecondofthethreequestionsI
distinguished.Itistheonethathasreceivedtheleastattention.InaskingitnowIdonot
meantobegoingbackonsomethingIsaidearlierwasundeniablytrue,viz.,thatifoneis
dreamingthatsomethingabouttheworldissoonedoesnottherebyknowthatitisso.
Thatstillseemstomeundeniable,butitisnotthesameasDescartes'sassumptionthat Page 16 of 27
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The Problem of the External World
one(p.24) mustknowthatoneisnotdreamingifoneistoknowsomethingaboutthe
world.Theundeniabletruthsaysonlythatyoulackknowledgeifyouaredreaming;
Descartessaysthatyoulackknowledgeifyoudon'tknowthatyouarenotdreaming.
Onlywiththestrongerassumptioncanhisscepticalconclusionbereached.
Isthatassumptiontrue?InsofaraswefindDescartes'sreasoningconvincing,oreven
plausible,Ithinkitisbecausewetooonreflectionfindthatitistrue.Isaidthatnotmuch
attentionhadbeenpaidtothatparticularpartofDescartes'sreasoning,andIthinkthat
tooisbecause,ashepresentsit,thestepseemsperfectlyconvincingandsoonlyother
partsoftheargumentappearvulnerable.Whyisthatso?IsitbecauseDescartes's
assumptionisindeedtrue?Isthereanythingwecandothatwouldhelpusdetermine
whetheritistrueornot?ThequestionisimportantbecauseIhavearguedsofarthatifit
istruewecanneverknowanythingabouttheworldaroundusonthebasisofthe
senses,andphilosophicalscepticismabouttheexternalworldiscorrect.Wewouldhave
tofindthatconclusionasconvincingorasplausibleaswefindtheassumptionfromwhich itisderived.
GivenouroriginalfavourableresponsetoDescartes'sreasoning,then,itcanscarcelybe
deniedthatwhatIhavecalledhisassumptionorconditionseemsperfectlynaturalto
insiston.Perhapsitseemslikenothingmorethananinstanceofafamiliarcommonplace
aboutknowledge.Weareallawarethat,eveninthemostordinarycircumstanceswhen
nothingveryimportantturnsontheoutcome,wecannotknowaparticularthingunless
wehaveruledoutcertainpossibilitiesthatwerecogniz eareincompatiblewithour knowingthatthing.
SupposethatonlookingoutthewindowIannouncecasuallythatthereisagoldfinchin
thegarden.IfIamaskedhowIknowitisagoldfinchandIreplythatitisyellow,weall
recogniz ethatinthenormalcasethatisnotenoughforknowledge.‘Forallyou'vesaidso
far,’itmightbereplied,‘thethingcouldbeacanary,sohowdoyouknowit'sa
goldfinch?’.AcertainpossibilitycompatiblewitheverythingIhavesaidsofarhasbeen
raised,andifwhat(p.25) IhavesaidsofarisallIhavegottogoonandIdon'tknow
thatthethinginthegardenisnotacanary,thenIdonotknowthatthereisagoldfinchin
thegarden.ImustbeabletoruleoutthepossibilitythatitisacanaryifIamtoknowthat
itisagoldfinch.Anyonewhospeaksaboutknowledgeandunderstandswhatotherssay
aboutitwillrecogniz ethisfactorconditioninparticularcases.
Inthisexamplewhatissaidtobepossibleissomethingincompatiblewiththetruthof
whatIclaimtoknow—ifthatbirdwereacanaryitwouldnotbeagoldfinchinthegarden,
butacanary.WhatIbelieveinbelievingitisagoldfinchwouldbefalse.Butthatisnotthe
onlywayapossibilitycanworkagainstmyknowledge.IfIcometosuspectthatallthe
witnesseshaveconspiredandmadeupastoryabouttheman'sbeinginClevelandthat
night,forexample,andtheirtestimonyisallIhavegottogooninbelievingthathewasin
Cleveland,ImightfindthatInolongerknowwhetherhewasthereornotuntilIhave
somereasontoruleoutmysuspicion.IftheirtestimonywereallinventedIwouldnot
knowthatthemanwasinCleveland.ButstrictlyspeakinghisbeinginClevelandisnot
incompatiblewiththeirmakingupastorysayinghewas.Theymighthaveinventeda Page 17 of 27
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The Problem of the External World
storytoprotecthim,whereasinfact,unknowntothem,hewasthereallthetime.Sucha
complicatedplotisnotnecessarytobringoutthepoint;Moore'sDukeofDevonshireis
enough.FromthefactthathewasdreamingthathewasspeakingintheHouseofLords
itdidnotfollowthathewasnotspeakingintheHouseofLords.Infacthewas.The
possibilityofdreaming—whichwasactualinthatcase—didnotimplythefalsityofwhat
wasbelieved.Apossibledeficiencyinthebasisofmybeliefcaninterferewithmy
knowledgewithoutitselfrenderingfalsetheverythingIbelieve.Ahallucinogenicdrug
mightcausemetoseemybedcoveredwithahugepileofleaves,forexample.5Having
takenthatdrug,IwillknowtheactualstateofmybedonlyifIknowthatwhatIseeisnot
justtheeffectofthedrug;ImustbeabletoruleoutthepossibilitythatIamhallucinating
thebedandtheleaves.Buthoweverimprobable(p.26) itmightbethatmybedis
actuallycoveredwithleaves,itsnotbeingcoveredwithleavesdoesnotfollowfromthe
factthatIamhallucinatingthatitis.WhatIamhallucinatingcouldneverthelessbe
(unknowntome)true.Butagoldfinchsimplycouldnotbeacanary.Soalthoughthereare
twodifferentwaysinwhichacertainpossibilitycanthreatenmyknowledge,itremains
truethattherearealwayscertainpossibilitieswhichmustbeknownnottoobtainifIam
toknowwhatIclaimtoknow.
Ithinkthesearejustfamiliarfactsabouthumanknowledge,somethingweallrecogniz e
andabidebyinourthoughtandtalkaboutknowingthings.Weknowwhatwouldbea
validchallengetoaclaimtoknowsomething,andwecanrecogniz etherelevanceand
forceofobjectionsmadetoourclaimstoknow.Thequestionbeforeusistowhatextent
Descartes'sinvestigationofhisknowledgethatheissittingbythefirewithapieceof
paperinhishandfollowstheserecogniz edeverydayproceduresforassessingclaimsto
know.Ifitdoesfollowthemfaithfully,andyetleadstotheconclusionthathecannotknow
whereheisorwhatishappeningaroundhim,weseemforcedtoaccepthisnegative
conclusionaboutknowledgeingeneraljustasweareforcedtoaccepttheconclusionthat
IdonotknowitisagoldfinchordonotknowthewitnesswasinClevelandbecauseI
cannotruleoutthepossibilitieswhichmustberuledoutifIamtoknowsuchthings.Is
Descartes'sintroductionofthepossibilitythathemightbedreamingjustlikethe
introductionofthepossibilitythatitmightbeacanaryinthegardenorthatthealibimight
becontrivedorthatitmightbeahallucinationofmybedcoveredwithleaves?
ThosepossibilitieswereallsuchthatiftheyobtainedIdidnotknowwhatIclaimedto
know,andtheyhadtobeknownnottoobtaininorderfortheoriginalknowledge‐claimto
betrue.DoesDescartes'sdream‐possibilityfulfilbothofthoseconditions?Ihavealready
saidthatitseemsundeniablethatitfulfilsthefirst.IfheweredreamingDescarteswould
notknowwhatheclaimstoknow.Someonewhoisdreamingdoesnottherebyknow
anythingabouttheworldaroundhimeveniftheworldaroundhimhappenstobejust
thewayhedreamsorbelievesittobe.Sohisdreamingisincompatible(p.27) withhis
knowing.Butdoesitfulfilthesecondcondition?Isitapossibilitywhichmustbeknownnot
toobtainifDescartesistoknowthatheissittingbythefirewithapieceofpaperinhis
hand?Ithinkitisdifficultsimplytodenythatitis.TheevidentforceofDescartes's
reasoningwhenwefirstencounteritisenoughtoshowthatitcertainlystrikesusasa
relevantpossibility,assomethingthatheshouldknownottoobtainifheistoknowwhere Page 18 of 27
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The Problem of the External World
heisandwhatishappeningaroundhim.
WhenthatpossibilitystrikesusasobviouslyrelevantinDescartes'sinvestigationwe
mightcometothinkthatitisbecauseofasimpleandobviousfactaboutknowledge.In
thecaseofthegoldfinchweimmediatelyrecogniz ethatImustknowthatitisnotacanary
ifIamtoknowitisagoldfinch.Anditisverynaturaltothinkthatthatissimplybecauseits
beingacanaryisincompatiblewithitsbeingagoldfinch.Ifitwereacanaryitwouldnotbe
agoldfinch,andIwouldthereforebewronginsayingthatitis;soifIamtoknowitisa
goldfinchImustruleoutthepossibilitythatitisacanary.Theideaisthatthetwo
conditionsIdistinguishedinthepreviousparagrapharenotreallyseparateafterall.As
soonasweseethatacertainpossibilityisincompatiblewithourknowingsuch‐and‐such,it
issuggested,weimmediatelyrecogniz ethatitisapossibilitythatmustbeknownnotto
obtainifwearetoknowthesuch‐and‐suchinquestion.Weseethatthedream‐possibility
satisfiesthatfirstconditioninDescartes'scase(ifheweredreaming,hewouldn'tknow),
andthatiswhy,accordingtothissuggestion,weimmediatelyseethatitisrelevantand
mustberuledout.Somethingweallrecogniz eaboutknowledgeiswhatissaidtomake thatobvioustous.
Butisthe‘simpleandobviousfactaboutknowledge’appealedtointhisexplanationreally
somethingthatistrueofhumanknowledgeeveninthemostordinarycircumstances?
Whatexactlyisthe‘fact’inquestionsupposedtobe?Ihavedescribeditsofar,asapplied
tothecaseofthegoldfinch,asthefactthatifIknowsomethingp(it'sagoldfinch)Imust
knowthefalsityofallthosethingsincompatiblewithp(e.g.,it'sacanary).Iftherewere
oneofthosethingsthatIdidnotknowtobefalse,anditwereinfacttrue,Iwouldnot
knowthatp,sinceinthatcasesomething(p.28) incompatiblewithpwouldbetrueand
sopwouldnotbetrue.ButtosaythatImustknowthatallthosethingsincompatiblewith
parefalseisthesameassayingthatImustknowthetruthofallthosethingsthatmust
betrueifpistrue.Anditisextremelyimplausibletosaythatthatisa‘simpleandobvious
fact’weallrecogniz eabouthumanknowledge.
Thedifficultyisthattherearenodeterminatelimitstothenumberofthingsthatfollow
fromthethingsIalreadyknow.ButitcannotbesaidthatInowknowallthose
indeterminatelymanythings,althoughtheyallmustbetrueifthethingsthatIalready
knowaretrue.EvengrantingthatInowknowagreatdealaboutalotofdifferentthings,
myknowledgeobviouslydoesnotextendtoeverythingthatfollowsfromwhatInow
know.Ifitdid,mathematics,totakeonlyoneexample,wouldbeagreatdealeasierthanit
is—orelseimpossiblydifficult.Inknowingthetruthofthesimpleaxiomsofnumber
theory,forexample,Iwouldtherebyknowthetruthofeverythingthatfollowsfrom
them;everytheoremofnumbertheorywouldalreadybeknown.Or,takingthe
pessimisticside,sinceobviouslynoonedoesknowallthetheoremsofnumbertheory,it
wouldfollowthatnooneevenknowsthatthosesimpleaxiomsaretrue.
Itisabsurdtosaythatweenjoyorrequiresuchvirtualomniscience,soitismore
plausibletoholdthatthe‘simpleandobviousfact’weallrecogniz eaboutknowledgeis
theweakerrequirementthatwemustknowthefalsityofallthosethingsthatweknowto
beincompatiblewiththethingsweknow.Iknowthatabird'sbeingacanaryis Page 19 of 27
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The Problem of the External World
incompatiblewithitsbeingagoldfinch;thatisnotsomefar‐flung,unknownconsequence
ofitsbeingagoldfinch,butsomethingthatanyonewouldknowwhoknewanythingabout
goldfinchesatall.AndtheideaisthatthatiswhyImustknowthatitisnotacanaryifIam
toknowthatitisagoldfinch.Perhaps,inordertoknowsomething,p,Idonotneedto
knowthefalsityofallthosethingsthatareincompatiblewithp,butitcanseemthatat
leastImustknowthefalsityofallthosethingsthatIknowtobeincompatiblewithp.Since
Iclaimtoknowthatthebirdisagoldfinch,andIknowthatitsbeingagoldfinchimplies
thatitisnotacanary,(p.29) Imustforthatreasonknowthatitisnotacanaryifmy
originalclaimistrue.InclaimingtoknowitisagoldfinchIwas,sotospeak,committing
myselftoknowingthatitisnotacanary,andImusthonourmycommitments.
Thisrequirementasitstands,evenifitdoesexplainwhyImustknowthatthebirdisnot
acanary,doesnotaccountfortherelevanceoftheothersortsofpossibilitiesIhave
mentioned.ThereasoninthegoldfinchcasewassaidtobethatIknowthatitsbeinga
canaryisincompatiblewithitsbeingagoldfinch.ButthatwillnotexplainwhyImustrule
outthepossibilitythatthewitnesseshaveinventedastoryabouttheman'sbeingin
Cleveland,orthepossibilitythatIamhallucinatingmybedcoveredwithapileofleaves.
NorwillitexplainwhyDescartesmustruleoutthepossibilitythatheisdreaming.WhatI
claimedtoknowinthefirstcaseisthatthemanwasinClevelandthatnight.But,aswe
sawearlier,itisnotaconsequenceofhisbeinginClevelandthatnoonewillinventastory
totheeffectthathewasinCleveland;theymightmistakenlybelievehewasnotthereand
thentellwhattheythinkisalie.Norisitaconsequenceofmybed'sbeingcoveredwith
leavesthatIamnothallucinatingthatitis.Butwerecognizethatinordertoknowinthose
casesIneverthelesshadtoruleoutthosepossibilities.Similarly,astheDukeof
Devonshireremindsus,itisnotaconsequenceofDescartes'ssittingbythefirewitha
pieceofpaperinhishandthatheisnotdreamingthatheis.Soifitisobvioustousthat
Descartesmustknowthatheisnotdreamingifheistoknowthatheissittingbythefire,
itcannotbesimplybecausethepossibilityinquestionisknowntobeincompatiblewith
whatheclaimstoknow.Itisnot.
Ifthereissome‘simpleandobviousfactaboutknowledge’thatwerecogniz eandrelyon
inrespondingtoDescartes'sreasoningitmustthereforebemorecomplicatedthanwhat
hasbeensuggestedsofar.Reflectingevenontheuncontroversialeverydayexamples
alonecaneasilyleadustosupposethatitissomethinglikethis:ifsomebodyknows
something,p,hemustknowthefalsityofallthosethingsincompatiblewithhisknowing
thatp(orperhapsallthosethingsheknowstobeincompatiblewithhisknowingthat
(p.30) p).Iwillnotspeculatefurtheronthequalificationsoremendationsneededto
maketheprinciplelessimplausible.Thequestionnowiswhetheritisouradherenceto
anysuchprincipleorrequirementthatisresponsibleforourrecognitionthatthe
possibilitythatthebirdisacanaryorthepossibilitythatthewitnessesmadeupastory
mustbeknownnottoobtainifIamtoknowthethingsIsaidIknewinthosecases.What
exactlyaretheproceduresorstandardswefollowinthemostordinary,humdrumcases
ofputativeknowledge?ReflectiononthesourceofDescartes'sscepticalreasoninghas
ledtodifficultiesindescribingandthereforeinunderstandingeventhemostfamiliar
procedureswefollowineverydaylife.Thatisoneoftherewardsofastudyof Page 20 of 27
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The Problem of the External World môn Principle of Management | Trường Đại học Quốc tế, Đại học Quốc gia Thành phố Hồ Chí Minh

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