牛津大学哲学概论PeterMillicanGeneraPhilosophyGeneralMT116PerceptionPQSQ.pptx

General PhilosophyDr Peter Millican,Hertford CollegeLecture 6:Perception and the Primary/Secondary Quality distinction2 2The Mechanisms of PerceptionThe“mechanical philosophy”of Descartes and others had to explain perception in terms of particles(or waves)affected by the objects and in turn impacting on our sense organs.Most discussion focused on sight and touch,the two senses that seem to come closest to presenting external objects as a whole.Lockes account was particularly influential,emphasising the primary/secondary distinction which had been implicit in Descartes.3 3What are Objects Like?Mechanical explanations of perception imply that our impressions of objects are conveyed by mechanisms whose stages(e.g.impact of particles on our sense organs)bear no resemblance to the objects themselves.The mechanical paradigm also suggests that objects fundamental properties will be those involved in mechanical interaction i.e.geometrical and dynamic properties.4 4Locke and CorpuscularianismLocke takes Boyles“corpuscularian hypothesis”(IV iii 16)as plausible:Properties of substances arise from theirProperties of substances arise from theirparticular micro-structure:composed ofparticular micro-structure:composed of“corpuscles”of“universal matter”(Boyle)“corpuscles”of“universal matter”(Boyle)or“pure substance in general”(Locke).or“pure substance in general”(Locke).Underlying substance has Underlying substance has primary qualitiesprimary qualities:shape,size,movement etc.,texture,and shape,size,movement etc.,texture,and“impenetrability”(Boyle)or“solidity”(Locke).“impenetrability”(Boyle)or“solidity”(Locke).Secondary qualitiesSecondary qualities(e.g.colour,smell,taste)are (e.g.colour,smell,taste)are powerspowers to cause ideas in us.to cause ideas in us.5 5Pains,Colours,and ShapesSuppose a circular hotplate on an oven is glowing red hot.I bring my hand close to it and feel warmth,then pain The sensations of felt warmth and pain are The sensations of felt warmth and pain are clearly“in the mind”.clearly“in the mind”.The circular shape of the hotplate is,we are The circular shape of the hotplate is,we are inclined to say,“really in the object”.inclined to say,“really in the object”.So is the red colour of the hotplate“in the So is the red colour of the hotplate“in the mind”or“in the object”?mind”or“in the object”?6 6A Problematic TextLockes Essay,II viii 10:“Such“Such QualitiesQualities,which in truth are nothing in,which in truth are nothing in the Objects themselves,but Powers to the Objects themselves,but Powers to produce various Sensations in us by their produce various Sensations in us by their primary Qualitiesprimary Qualities,i.e.i.e.by the Bulk,Figure,by the Bulk,Figure,Texture,and Motion of their insensible parts,Texture,and Motion of their insensible parts,as Colours,Sounds,Tasts,as Colours,Sounds,Tasts,etc.etc.These I call These I call secondary Qualitiessecondary Qualities.The comma before“but”is unfortunate.Locke means“nothing but powers”.7 7In Objects,or Just In the Mind?Locke sees Locke sees bothboth PQs and SQs as genuine PQs and SQs as genuine properties of objects,but the SQs are nothing properties of objects,but the SQs are nothing but but powers due to their PQspowers due to their PQs.Berkeley read Locke as saying that SQs are only Berkeley read Locke as saying that SQs are only“in the mind”and“in the mind”and notnot really properties of objects.really properties of objects.But Locke is clear that our simple perceptions of But Locke is clear that our simple perceptions of objects colour etc.are“adequate”:they objects colour etc.are“adequate”:they faithfullyfaithfully represent their“archetypes”(II xxxi 1,12):represent their“archetypes”(II xxxi 1,12):“SimpleSimple Ideas are certainly Ideas are certainly adequateadequate.Because.Because being intended to express nothing but the power in being intended to express nothing but the power in Things to produce in the Mind such a Sensation”Things to produce in the Mind such a Sensation”8 8Why Resemblance?Hence Lockes emphasis on resemblance,rather than real existence in objects,as the key distinction between PQs and SQs:“the“the Ideas of primary QualitiesIdeas of primary Qualities of Bodies,of Bodies,are are Resemblances Resemblances of them,and their Patterns do of them,and their Patterns do really exist in the Bodies themselves;but the really exist in the Bodies themselves;but the Ideas,producedIdeas,produced in us in us byby these these Secondary Secondary Qualities,have no resemblanceQualities,have no resemblance of them at all.of them at all.There is nothing like our There is nothing like our IdeasIdeas,existing in the,existing in the Bodies themselves.”(Bodies themselves.”(EssayEssay II viii 15)II viii 15)9 9Can an Idea Resemble an Object?Berkeley(Principles I 8)is emphatic that:“an idea can be like nothing but an idea;a“an idea can be like nothing but an idea;a colour or figure can be like nothing but another colour or figure can be like nothing but another colour or figure.”colour or figure.”His attack on Lockes resemblance thesis seems to be based on the principle that ideas are intrinsically“perceivable”.This is very plausible for SQs nothing can be like a sensed smell,or colour,unless it is mental(as with a felt pain).1010Structural Resemblance?But ideas of PQs seem to lack this intimate connexion with mentality they are more abstract and structural,as illustrated by their use in geometrical mechanics.We can use these“mathematical”properties to calculate predictions about objects behaviour,and find that these“work”.So its plausible that ideas of PQs can resemble non-mental reality in a structural way(cf.Lowe on Locke,pp.57,63-4).1111SolidityHowever solidity seems to be an odd man out our idea of solidity seems clearly to be the idea of a power(or rather,perhaps,the unknown ground of a power),and without any resemblance to a property of objects.Solidity is a power or a disposition to exclude other bodies.But what is a body?Body is distinguished from empty space by its solidity,so the whole thing is circular!1212Humes Criticism(Treatise I iv 4)“Two non-entities cannot exclude each other from“Two non-entities cannot exclude each other from their places Now I ask,what idea do we form of their places Now I ask,what idea do we form of these bodies or objects,to which we suppose these bodies or objects,to which we suppose solidity to belong?To say,that we conceive them solidity to belong?To say,that we conceive them merely as solid,is to run on merely as solid,is to run on in infinitumin infinitum.Extension must necessarily be considerd either as Extension must necessarily be considerd either as colourd,which is a false idea because its a SQ,colourd,which is a false idea because its a SQ,supposed not to be“in”objects;or as solid,which supposed not to be“in”objects;or as solid,which brings us back to the first question.Hence brings us back to the first question.Hence after the exclusion of colours(etc.)from the rank of after the exclusion of colours(etc.)from the rank of external existences,there remains nothing,which external existences,there remains nothing,which can afford us a just and consistent idea of body.”can afford us a just and consistent idea of body.”1313Empiricism and UnderstandingThe attack on resemblance thus leads naturally to an attack based on our lack of understanding of the qualities concerned.If all our ideas are derived from experience(as Locke had insisted),then our ideas of PQs(e.g.shape)will naturally be infused with those of the SQs by which we perceive them(e.g.a colour that fills the space).And if these SQs cannot be understood as existing outside a mind 1414The Attack on AbstractionSo Berkeley and Hume attack Locke on the grounds that we cant form a coherent idea of matter without using ideas of SQs.They see Locke as illegitimately trying to“abstract”a purely PQ idea of body away from our actual idea which is inextricably bound up with perceptual notions.Hence their focus on abstraction(see the Introduction to Berkeleys Principles).1515The Case for IdealismBerkeley concludes fromthis argument that bodiesindependent of mind areliterally inconceivable.If this works,it seems toshow that the only way wecan make sense of theworld is as fundamentally consisting of mental entities(i.e.“spirits”and“ideas”.1616“Something I Know Not What”To defend realism we should accept that our idea of body is“inadequate”we cant conceive of what it is that fills space except in terms of“what it does”(cf.Essay II xxiii 2).More modern concepts such as mass and electric charge make this clearer:we are under no illusion that the basic properties employed in our scientific theories have to be directly perceivable,or understandable in non-dispositional terms.1717Lockes Indirect RealismIdea in the mindIdea in the mind(directly perceived)(directly perceived)Material objectMaterial object(cause of the idea)(cause of the idea)The“Veil of perception”problem:how can we know whether there is a real material object?1818An Unacceptable InterpretationIndirect realism is sometimes parodied as the view that in order to perceive a tree,I must perceive an image-of-a-tree(as though some sort of“homunculus”is sitting in my head viewing a little projector screen).However this clearly doesnt explain perception,because it presupposes that the image-of-a-tree is itself perceived.If it can be“directly”perceived,why cant the tree?1919Sense DataTwentieth-century philosophers such as Ayer prefer the term“sense-data”to Lockes“idea”,but this rather lends itself to the unacceptable interpretation.Its better to say that awareness of a“sense-datum”counts as perception of an external object if it was caused appropriately by such an object.But how can I know that it was so caused?Again we face the“veil of perception”.2020How To Prove the Causal Link?“It is a question of fact,whether the perceptions“It is a question of fact,whether the perceptions of the senses be produced by external objects,of the senses be produced by external objects,resembling them:How shall this question be resembling them:How shall this question be determined?By experience surely But here determined?By experience surely But here experience is,and must be entirely silent.The experience is,and must be entirely silent.The mind has never any thing present to it but the mind has never any thing present to it but the perceptions,and cannot possibly reach any perceptions,and cannot possibly reach any experience of their connexion with objects.The experience of their connexion with objects.The supposition of such a connexion is,therefore,supposition of such a connexion is,therefore,without any foundation in reasoning.”without any foundation in reasoning.”(Hume,(Hume,EnquiryEnquiry 12.12)12.12)2121PhenomenalismPhenomenalism is the view that physical objects are logical constructions out of sense-data.So statements about such objects are interpreted as stating what would be perceived in certain circumstances.This aims to evade the Berkeleian argument This aims to evade the Berkeleian argument that one cannot make sense of physical objects that one cannot make sense of physical objects in abstraction from perceptions;in abstraction from perceptions;It also aims to answer the Humean argument of It also aims to answer the Humean argument of the veil of perception.the veil of perception.2222Direct RealismRather than resort to phenomenalism,a more popular recent view(since J.L.Austin and P.F.Strawson)has been to insist that we perceive objects directly.This seems right,in so far as it is intended to This seems right,in so far as it is intended to counter the Unacceptable Interpretation.counter the Unacceptable Interpretation.However it doesnt solve the sceptical problems,However it doesnt solve the sceptical problems,and can seem merely verbal:it is accepted that and can seem merely verbal:it is accepted that our perception is our perception is mediatedmediated physicallyphysically(by light (by light rays etc.);the point is just that rays etc.);the point is just that we do perceive we do perceive objects(and see them objects(and see them as objectsas objects)by that means.by that means.2323Is a Lockean View Defensible?A live Lockean option is to see an“idea”as an A live Lockean option is to see an“idea”as an intentional objectintentional object the object as it appearsthe object as it appears(cf.(cf.Mackie on Locke,pp.47-51).Mackie on Locke,pp.47-51).This is purely mental,not any sort of image on a This is purely mental,not any sort of image on a screen(or a retina).Indeed it is not really any sort screen(or a retina).Indeed it is not really any sort of of objectobject at all.Nor is it an attempt to at all.Nor is it an attempt to explainexplain perception.The point is to insist that our visual perception.The point is to insist that our visual experience(though only experience(though only describabledescribable in terms of in terms of apparent objects)is in principle distinguishable apparent objects)is in principle distinguishable from the from the existenceexistence of those objects.In that sense of those objects.In that sense it is still a“representative”theory of perception.it is still a“representative”theory of perception.2424Explanatory RealismThen Lockean“indirect”realism can be defended as scientifically explanatory(in line with its original motivation).How things appear to us is explicable in terms of How things appear to us is explicable in terms of mechanisms involving external objects,physical mechanisms involving external objects,physical intermediaries etc.intermediaries etc.These explanations appeal to objects“real”These explanations appeal to objects“real”qualities(which need not qualities(which need not resembleresemble our ideas)our ideas)and explain illusions,and explain illusions,bothboth of SQs and PQs(to of SQs and PQs(to answer Berkeleys argument from illusion).answer Berkeleys argument from illusion).