GeneralGeneral PhilosophyPhilosophy

DrDr PeterPeter MillicanMillican,, HertfordHertford CollegeCollege

LectureLecture 4:4: TwoTwo CartesianCartesian TopicsTopics Scepticism,Scepticism, andand thethe MindMind

LastLast TimeTime …… … we looked at scepticism about INDUCTION. ThisThis LectureLecture …… … will move on to SCEPTICISM concerning the external world, most famously exemplified in Descartes’ first Meditation, and his related claims about the nature of MIND AND BODY. TheThe NextNext LectureLecture …… … will say more about modern responses to SCEPTICISM, and focus on KNOWLEDGE. 2 TwoTwo KindsKinds ofof ScepticismScepticism

VerticalVertical ScepticismScepticism – Inferring from one kind of thing to a different kind (e.g. inferring from one’s sensations or appearances, to the existence of real physical objects that cause them). HorizontalHorizontal ScepticismScepticism – Inferring things of the same kind as one has experienced (e.g. inferring from one’s sensations or appearances, to expect similar sensations or appearances in the future).

3 ExternalExternal WorldWorld ScepticismScepticism

ItIt cancan seemseem thatthat ((““verticalvertical””)) externalexternal worldworld scepticismscepticism isis farfar moremore worryingworrying thanthan ((““horizontalhorizontal””)) inductiveinductive scepticism:scepticism: – Maybe I am just dreaming, and there is no external world at all. – Maybe an evil demon is causing me to have illusions of an external world. – Maybe a wicked scientist has my brain in a vat, and is creating these illusions.

4 DescartesDescartes’’ ApproachApproach

TheThe onlyonly wayway toto defeatdefeat scepticismscepticism isis toto withholdwithhold assentassent fromfrom anythinganything thatthat isnisn’’tt completelycompletely certain.certain. WhenWhen II considerconsider ““II think,think, thereforetherefore II amam””,, itit isis quitequite impossibleimpossible forfor meme toto bebe mistaken.mistaken. SoSo II amam completelycompletely certaincertain ofof this,this, atat least.least. ByBy contemplatingcontemplating thisthis firstfirst certainty,certainty, II understandunderstand whatwhat makesmakes itit certaincertain isis thatthat II clearlyclearly andand distinctlydistinctly perceiveperceive itit toto bebe true.true.

5 DescartesDescartes andand GodGod

HenceHence II cancan establishestablish asas aa generalgeneral rulerule thatthat anythinganything II clearlyclearly andand distinctlydistinctly perceiveperceive isis truetrue.. II clearlyclearly andand distinctlydistinctly perceiveperceive thatthat GodGod mustmust exist,exist, becausebecause onlyonly aa perfectperfect beingbeing couldcould bebe thethe ultimateultimate causecause ofof suchsuch aa perfectperfect ideaidea asas mymy ideaidea ofof God.God. AA perfectperfect GodGod cannotcannot deceive,deceive, soso II knowknow thatthat mymy facultiesfaculties areare essentiallyessentially reliable.reliable.

6 TheThe CartesianCartesian CircleCircle

DescartesDescartes seemsseems toto bebe ““boot-strappingboot-strapping””:: – proving the existence of God by relying on his mental faculties. – then appealing to the existence of God to justify reliance on his mental faculties. IsnIsn’’tt thisthis viciouslyviciously circular?circular? – If my faculties might be defective, then how can I trust my proof of the existence of God in the first place? How can any anti-sceptical argument even get off the ground? 7 MooreMoore’’ss ResponseResponse

G.E.G.E. MooreMoore famouslyfamously claimedclaimed toto refuterefute thisthis sortsort ofof scepticismscepticism byby appealappeal toto common-common- sensesense knowledge:knowledge: – Here’s one hand [he holds up a hand], and here’s another [he holds up the other]. – If this is a hand, then there is an external world. – Therefore there is an external world, and scepticism is refuted.

8 TwoTwo ArgumentsArguments fromfrom ““PP impliesimplies QQ””

ModusModus PonensPonens P implies Q P → Q P is true P therefore Q is true ∴ Q

ModusModus TollensTollens P implies Q P → Q Q is false ¬Q therefore P is false ∴ ¬P

9 OneOne personperson’’ss modusmodus ponensponens ……

Deuteronomy 20:16-17 commands multiple genocide to avoid religious pollution. TheThe religiousreligious fundamentalistfundamentalist mightmight say:say: Everything in the Bible is true. Therefore genocide is sometimes desirable. TheThe humanehumane philosopherphilosopher wouldwould say:say: Genocide is never desirable. Therefore not everything in the Bible is true. WhichWhich underlinedunderlined premisepremise isis moremore plausible?plausible?

10 …… isis anotheranother’’ss modusmodus tollenstollens ……

– If this is a hand, then there is an external world. MooreMoore says:says: – We know this is a hand. – Therefore we know there is an external world. TheThe scepticsceptic says:says: – We don’t know that there is an external world. – Therefore we don’t know that this is a hand. MooreMoore willwill claimclaim thatthat hishis premisepremise isis moremore plausibleplausible thanthan thethe scepticsceptic’’s.s. 11 InternalismInternalism andand ExternalismExternalism

WeWe’’dd likelike toto agreeagree withwith Moore,Moore, butbut itit seemsseems hardhard toto justifyjustify aa claimclaim toto knowledgeknowledge soso crudely:crudely: dondon’’tt wewe needneed somesome philosophicalphilosophical argumentargument ratherrather thanthan aa barebare common-sensecommon-sense claimclaim toto justifyjustify knowingknowing thatthat thisthis isis aa hand?hand? ButBut ““internalistinternalist”” arguments,arguments, likelike CartesianCartesian boot-strapping,boot-strapping, havehave difficultydifficulty doingdoing thethe job.job. SoSo manymany recentrecent philosophersphilosophers havehave movedmoved towardstowards externalismexternalism (next(next lecture,lecture, andand comparecompare MellorMellor’’ss approachapproach toto induction).induction).

12 CartesianCartesian DualismDualism

TheThe viewview forfor whichwhich DescartesDescartes isis nownow bestbest known:known: – The body is material, composed of matter whose essence (i.e. fundamental property from which other properties follow) is extension. – The mind is composed of immaterial substance whose essence is thinking. ThisThis substancesubstance dualismdualism isis toto bebe contrastedcontrasted withwith propertyproperty dualismdualism (i.e.(i.e. therethere areare bothboth physicalphysical andand non-physicalnon-physical propertiesproperties).). 13 AA BadBad ArgumentArgument forfor DualismDualism

InIn hishis DiscourseDiscourse,, DescartesDescartes arguesargues likelike this:this: I can doubt that my body exists. I cannot doubt that I exist. ∴ I am not identical with my body. Compare:Compare: I can doubt that Hesperus is Phosphorus. * I cannot doubt that Phosphorus is Phosphorus. ∴ Hesperus is not Phosphorus.

* Hesperus = the Evening Star; Phosphorus = the Morning Star; in fact both are appearances of the planet Venus. 14 LeibnizLeibniz’’ss LawLaw

IfIf aa andand bb areare thethe samesame thing,thing, thenthen anyany propertyproperty ofof aa mustmust alsoalso bebe aa propertyproperty ofof bb:: Fa, a=b ╞ Fb – If F is the property of being doubted by me to exist, a is me, and b is my body, we get Descartes’ argument from the Discourse. – Likewise F could be the property of being doubted by me to be Prime Minister (etc.) ToTo simplestsimplest wayway toto avoidavoid thethe fallacyfallacy isis toto denydeny thatthat thesethese areare genuinegenuine properties.properties. 15 AA BetterBetter ArgumentArgument forfor DualismDualism

DescartesDescartes’’ argumentargument inin MeditationMeditation VIVI isis lessless fallacious,fallacious, butbut hashas questionablequestionable premises:premises: – I have a clear understanding of myself as (potentially) a thinking, non-extended thing. – I have a clear understanding of body as (potentially) extended and non-thinking. – Anything I clearly and distinctly understand could be created by God accordingly. – So I could exist separately from my body, and it follows that I am genuinely distinct from it. 16 FromFrom DoubtDoubt toto EssenceEssence

EvenEven inin thethe MeditationsMeditations,, DescartesDescartes triestries toto motivatemotivate hishis claimclaim toto knowknow thethe essenceessence ofof mindmind (as(as thinking)thinking) fromfrom hishis doubtdoubt argument:argument: “what shall I now say that I am [when I might be deceived by an evil demon, or dreaming]? … At present I am not admitting anything except what is necessarily true. I am, then, in a strict sense only a thing that thinks; that is, I am a mind, or intelligence, or intellect, or reason … what kind of thing? … a thinking thing.

17 EpistemologyEpistemology →→ Metaphysics?Metaphysics?

TheThe wayway inin whichwhich wewe comecome toto knowknow,, oror bebe certain,certain, ofof somethingsomething needneed notnot reflectreflect itsits ultimateultimate naturenature (or(or whywhy itit isis thatthat wayway).). – From I am thinking, it plausibly follows that (in at least one sense) I am a thing that thinks. – But it does not necessarily follow that I am something whose essence is to think. – Nor does it follow that the thing that thinks could exist without being extended. (Imagine if a piece of matter were made able to think.) 18 PossiblyPossibly DistinctDistinct →→ ActuallyActually Distinct?Distinct?

TheThe finalfinal movemove ofof DescartesDescartes’’ argumentargument seemsseems moremore defensible,defensible, inin aa sense:sense: God could have created my mind and body as separate entities. ∴ It is possible for my mind and body to exist separately. ∴ My mind and body are in fact distinct things. ButBut ““couldcould havehave”” mustmust bebe metaphysicalmetaphysical possibility,possibility, notnot epistemologyepistemology ((““mightmight havehave forfor allall II knowknow””).). SoSo thisthis begsbegs thethe question.question. 19 TheThe DistinctDistinct SubstancesSubstances ProblemProblem

““HowHow cancan twotwo suchsuch distinctdistinct substancessubstances interactinteract atat all?all?”” – A problem for Descartes, who takes causation to be ultimately intelligible. – Not a problem in principle on a Humean view of causation: causation is a matter of lawlike correlation rather than intelligible connexion. – But it’s hard to see what such “laws” could be like, so a difficulty remains (cf. the “explanatory gap” between physical and mental).

20 TheThe CausalCausal ClosureClosure PrinciplePrinciple

TheThe causalcausal closureclosure principleprinciple isis thatthat physicalphysical eventsevents (or(or theirtheir probabilities)probabilities) areare determineddetermined entirelyentirely byby physicalphysical causes.causes. – Also called “the completeness of physics”. – In this form, the principle is compatible with physical events’ being to some extent random. – Casts doubt on non-physical causation. CommonlyCommonly believed,believed, thoughthough itsits evidentialevidential basebase isis notnot soso clear.clear.

21 ProblemsProblems ExplainingExplaining InteractionInteraction

TheThe causalcausal closureclosure principleprinciple seemsseems toto leaveleave nono roomroom forfor aa distinctdistinct mentalmental substancesubstance capablecapable ofof influencinginfluencing thethe body.body. EvenEven ifif wewe denydeny thethe principle,principle, mind/bodymind/body interactioninteraction seemsseems mysterious.mysterious. ItIt’’ss hardhard toto seesee howhow anan immaterialimmaterial mindmind couldcould havehave evolvedevolved alongsidealongside thethe body.body. – Do animals have one too? – Is having a mind “all or nothing”?

22 MindMind andand Body:Body: DifferentDifferent ViewsViews InteractionismInteractionism – The mind can causally influence the body (e.g. movement), and vice-versa (e.g. pain). EpiphenomenalismEpiphenomenalism – The mind is an “epiphenomenon” – caused by events in the brain, but itself causally inert. (this account is particularly hard to square with evolution – how could such a mind evolve?) PhysicalismPhysicalism – Only physical things exist, hence there is nothing to the mind beyond the physical brain. 23 TheThe KnowledgeKnowledge ArgumentArgument (Jackson)(Jackson)

ImagineImagine aa scientistscientist (Mary)(Mary) whowho learnslearns allall thethe physicalphysical factsfacts aboutabout colourcolour andand colourcolour perception,perception, butbut whowho cancan seesee onlyonly inin black,black, white,white, andand shadesshades ofof grey.grey. IfIf sheshe thenthen acquiresacquires normalnormal sight,sight, whenwhen sheshe seessees colourscolours sheshe learnslearns whatwhat theythey looklook likelike,, somethingsomething sheshe didndidn’’tt knowknow before.before. HenceHence thesethese phenomenalphenomenal colourcolour propertiesproperties cannotcannot bebe physical.physical. WeWe areare forcedforced intointo propertyproperty dualism,dualism, ifif notnot substancesubstance dualism.dualism. 24 WhatWhat isis aa PhysicalPhysical Cause?Cause?

WhatWhat areare thethe propertiesproperties ofof physicalphysical matter?matter? – If matter is just inert, extended (and possibly impenetrable) stuff, then it’s hard to see how it could possibly be the causal basis of thought. – But quantum “matter” has all sorts of weird properties: charge, spin, “charm”, “strangeness”. – Could matter have some proto-psychic property too (panpsychism: mind is a fundamental feature of the universe)? Would this then be physical?! – Physicalism generally shuns such “spooks”. 25 Non-PhysicalNon-Physical ExplanationExplanation

EvenEven withwith ““non-spookynon-spooky”” physicalism,physicalism, itit doesndoesn’’tt followfollow thatthat everythingeverything inin thethe worldworld cancan bebe explainedexplained inin physicalphysical terms.terms. – Why does my calculator show “132” when I type “11 x 12 =“ ? – Answer: because 11 x 12 is equal to 132. The explanation appeals to mathematical facts, not just physical facts about the calculator. LikewiseLikewise evolutionaryevolutionary explanationexplanation etc.etc. (e.g.(e.g. inin termsterms ofof thethe logiclogic ofof gamegame theory).theory). 26 TheThe Hardware/SoftwareHardware/Software AnalogyAnalogy

ItIt isis temptingtempting toto seesee thethe relationrelation betweenbetween brainbrain andand mindmind asas analogousanalogous toto thatthat betweenbetween hardwarehardware andand software.software. – This treats the mind as clearly distinguishable from the body, but not a distinct substance. ExplainsExplains awayaway anotheranother CartesianCartesian argument:argument: Body is divisible. Mind is not divisible. ∴ Body and mind are distinct.

27 RyleRyle andand CategoryCategory MistakesMistakes

TheThe classicclassic categorycategory mistake:mistake: – “I’ve seen all these colleges and offices, but where is the University?” – Supposes the University to be a separate thing. ““MindMind”” asas aa categorycategory mistake:mistake: – “People behave in these various ways, so they must have a mind distinct from their body.” – Instead, “having a mind” just is a matter of how one behaves. It’s not a separate thing.

28 StrawsonStrawson andand ““ManyMany MindsMinds””

IfIf oneone doesdoes thinkthink ofof thethe mindmind asas aa separateseparate thingthing fromfrom thethe body,body, anan ““entityentity”” inin itsits ownown right,right, thenthen thisthis raisesraises thethe questionquestion ofof howhow suchsuch entitiesentities areare toto bebe individuatedindividuated.. HowHow cancan II knowknow mymy brainbrain isnisn’’tt linkedlinked toto lotslots ofof differentdifferent mindsminds thinkingthinking inin unison?unison? – Possible answer: I can’t be certain, but it’s an extravagant and arbitrary hypothesis. – However Strawson would probably see even the possibility as a reductio ad absurdum. 29 TheThe HardHard ProblemProblem

PhysicalismPhysicalism cancan comfortablycomfortably accommodate:accommodate: – Non-physical explanation (e.g. in terms of purposes, as with a chess computer); – A notion of “mind” analogous to software. ButBut thethe ““hardhard problemproblem”” (Chalmers)(Chalmers) remains:remains: – Why is all this accompanied by phenomenal consciousness (i.e. conscious experience)? CanCan thisthis justifyjustify substancesubstance dualismdualism afterafter all?all? – Or should we rather admit that we simply don’t

30 (yet) understand it? Maybe we never will!