Perception 2016 revision 2. indirect realism part 2

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  1. Indirect Realism 2. The Syllabus: Indirect Realism ã the immediate objects of perception are mind- dependent objects that are caused by and represent mind-…
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  • 1. Indirect Realism
  • 2. The Syllabus: Indirect Realism • the immediate objects of perception are mind- dependent objects that are caused by and represent mind- independent objects. • Issues, including: – it leads to scepticism about the ‘existence’ of the external world (attacking ‘realism’) – responses to this (external world is the ‘best hypothesis’ (Russell); coherence of the various senses and lack of choice over our experiences (Locke)) – it leads to scepticism about the ‘nature’ of the external world (attacking ‘representative’) - responses (sense data tell us of ‘relations’ between objects (Russell); the distinction between primary and secondary qualities (Locke)) – problems arising from the view that mind-dependent objects represent mind-independent objects and are caused by mind-independent objects.
  • 3. Indirect Realism • Indirect realism: the immediate objects of perception are mind-dependent objects that are caused by and represent mind- independent objects. • Indirect Realists: John Locke, Rene Descartes, David Hume, Bertrand Russell etc
  • 4. Problem 2: Can we know the external world as it really is? Some sceptical thoughts. • Assume, hypothetically, that the external world does exist (accept the argument from best explanation!) – But what is the world’s nature? • Key Question: If we know it only through representations, could there be a gap between how we see the world and how it really is? – Re + Presentation – even the shape of this word shows there is a gap… – How representative is our view of the way the world really is? • [Worse: solipsism…If sense-data are private to the individual: could there be a gap between how the individual sees the world, and how others see it? • Might the world of representations have only one inhabitant?] How can you check the correctness of your mental image if you don’t have direct access to the real? How can you check the reality of the cinematic image, if you cannot leave the cinema?
  • 5. Responses to this criticism ‘Sense data’ tell us of ‘relations’ between objects – Russell. ‘We agreed provisionally that physical objects cannot be quite like our sense- data, but may be regarded as causing our sensations. … we may assume that there is a physical space in which physical objects have spatial relations corresponding to those which the corresponding sense-data have in our private spaces…we cannot have that immediate acquaintance with physical distances that we have with distances in our private spaces, or with colours or sounds or other sense-data. …although the relations of physical objects have all sorts of knowable properties, derived from their correspondence with the relations of sense-data, the physical objects themselves remain unknown in their intrinsic nature, so far at least as can be discovered by means of the senses. [Still, the] most natural, though not ultimately the most defensible, hypothesis to adopt in the first instance…would be that, though physical objects cannot, for the reasons we have been considering, be exactly like sense-data, yet they may be more or less like’ • How satisfactory is Russell’s reply: ‘we can’t know things as they are, but only the relations between them?’ • Is this an experiential answer, or a logician’s?
  • 6. Russell’s Argument in more detail • His argument: given the argument from perceptual variation, it is clear that physical space (the space of science) and apparent space (space as we experience it) are not the same. • But they are connected in a detailed, systematic, and predictable way. – Objects cause sense-data, so our bodies are causally affected by objects. – The relative positions of objects in physical space correspond to the relative positions of sense-data in apparent space. (Block 3 looks further away than Block 1; it takes us longer to walk there, therefore) – We can’t know physical objects in themselves, but we can know that the relationships between sense-data and (assumed, underlying) physical objects must correspond. • The same argument works for time: – physical time and apparent time are not experientially the same (ever been in a lesson that dragged out?) – But even when time-sense varies between perceivers, events occur in the same sequence • The same argument works for colour, and all other qualities. – If two objects look the same under the same viewing conditions, then they have something in common. If they look different, they do not. If two objects feel, smell, taste the same… – We can’t know what it is about the physical objects in themselves that enables these relationships. But we can know that the relationships exist.
  • 7. Issues with Russell’s response • But: is it satisfactory to reduce our knowledge of the world to knowledge of sense-data, and knowledge of the relationships between sense-data? • How much of an advance is it to claim that sense-data tell us only about real relations between objects, objects which we cannot experience directly? • We may be able to hypothesise a ‘real’ physical space, but how are we helped by this notion if we cannot experience this space ourselves? • How can we be confident that our sense-data are ‘more or less like’ the underlying objects that produce them? (Russell admits that his assertion that they are is not very ‘defensible’.) • He seems to admit that at best it only seems that we perceive mind-independent objects. – This is counter-intuitive: try describing what you experience in terms of pure sense- data without bringing in physical object terms… – Are physical object terms merely ‘shorthand’ for collections of sense-data? Task: Describe an everyday physical object using only sense-data terms.
  • 8. Locke’s Notion of Primary and Secondary Qualities • Locke argues that his distinction between primary and secondary qualities explains the nature of the external world. • Text source: Essay Concerning Human Understanding, Book 2 chs. 8 and 21 • Our encounters with material bodies (i.e. physical objects) leads to their producing various ideas in us. – E.g. Our experience of a particular Granny Smith apple produces ideas of a certain roundish shape, a certain size, a certain range of green shades, a certain tart taste, and certain crisp texture etc… • Locke distinguishes the qualities (=properties) of the material objects from the ideas (of those qualities) in our mind. – Qualities are in the external objects. – Ideas (of qualities) are in the mind.
  • 9. Locke on Qualities and Ideas (of Qualities) taken from his ‘An Essay Concerning Human Understanding’ (1690) 8. [Ideas and Qualities] Whatsoever the mind perceives in itself, or is the immediate object of perception, thought, or understanding, that I call idea; and the power to produce any idea in our mind, I call a quality of the subject wherein that power is. Thus a snowball having the power to produce in us the ideas of white, cold, and round, as they are in the snowball, I call qualities; and as they are sensations or perceptions in our understandings, I call them ideas; Explain Locke’s distinction between ideas and qualities.
  • 10. PRIMARY QUALITIES (shape, size, motion, solidity) • Definitions: – ‘Motion’ = the states of moving or being at rest – ‘Solidity’ = occupies 3D space in some manner (modern quantum physics has redefined this property somewhat) • Primary qualities are intrinsic qualities in bodies: physical objects must have these qualities. • The idea of a physical object always includes its being a size, a shape, being in rest or motion, occupying space. • These qualities are mind-independent and objective. • And: our ideas of these primary qualities resemble the qualities themselves.
  • 11. SECONDARY QUALITIES (colors, odors, tastes, textures, sounds) • These qualities are perceiver-dependent and therefore subjective. • Physical objects can be conceived of without them: there can be e.g. odourless, intangible (=without feel), transparent (=without colour) things. • Secondary qualities are in material bodies only as causal powers (resulting from the PQs) to cause certain sorts of sensation in minds like ours. – These causal powers result from the PQs: a particular microstructure of PQs interacts with our senses to produce such-and-such a sensation in us. • So the secondary qualities are really nothing in the object beyond the primary qualities and so our ideas of these secondary qualities in no way resemble the qualities themselves.
  • 12. Primary versus Secondary • Primary qualities are objective and invariant. – They do not depend on human perception. – A being who lacks vision could understand e.g. a square shape…(bats!) – Bernard Williams: ‘”What is real is accessible from any point of view” • Secondary properties such as colours, sounds are not real properties of objects, but are mutable and subjective. – They do depend on human perception. – What we perceive of as colours, noises, smells would not be perceived as such by other creatures (bats!) • Yet primary qualities cause secondary ones. • So our mutable sensory experience rests on something wholly enduring.
  • 13. How do secondary qualities relate to primary ones? • caused by, reducible to primary qualities (movement, shape, size). • so perceiver-dependent qualities are caused by perceiver- independent ones. • so (assumption) they are good representations of (= systematically correlated with) the world of primary qualities. Scientific account of sound: sound is movement of air molecules Scientific account of taste: taste is shape of scent molecules
  • 14. Locke’s distinction between Primary and Secondary Qualities 9. [Primary qualities] Some qualities…are utterly [constant and] inseparable from the body, in whatever state it be, [regardless of] all the alterations and changes it suffers…e.g. Take a grain of wheat, divide it into two parts; each part has still solidity, extension, figure, and mobility [or rest and motion]: divide it again, and it retains still the same qualities [and so on, regardless of how small it becomes]… these I call original or primary qualities of body 10. [Secondary qualities of bodies] Secondly, such qualities which in truth are nothing in the objects themselves but power to produce various sensations in us by their primary qualities, i.e. by the bulk, figure, texture, and motion of their insensible parts, as colours, sounds, tastes, &c. These I call secondary qualities. … 11. [How bodies produce ideas in us] Bodies produce ideas in us…[primary qualities cause external] motions…continued by our nerves, or animal spirits…to the brains or the seat of sensation, there to produce in our minds the particular ideas we have of them…
  • 15. Locke: only primary qualities are mind-independent 17. [Only primary qualities exist independently of being perceived] The particular bulk, number, figure, and motion of the parts of fire or snow are really in them,— whether any one’s senses perceive them or no: and therefore they may be called real qualities…But light, heat, whiteness, or coldness are not…Take away the sensation of them; let not the eyes see light or colours, nor the ears hear sounds; let the palate not taste, nor the nose smell, and all colours, tastes, odours, and sounds, as they are such particular ideas, vanish and cease, and are reduced to their causes, i.e. bulk, figure, and motion of parts.
  • 16. Locke: primary qualities cause secondary ones. 18. [Secondary qualities exist in things only because of primary qualities] Let us consider the red and white colours in porphyry [purple stone with white flecks]. Hinder light from striking on it, and its colours vanish; it no longer produces any such ideas in us: upon the return of light it produces these appearances on us again. Can any one think any real alterations are made in the porphyry by the presence or absence of light… it is plain it has no colour in the dark…It has, indeed, such a configuration of particles, both night and day, as are apt, by the rays of light rebounding from some parts of that hard stone, to produce in us the idea of redness, and from others the idea of whiteness; but whiteness or redness are not in it at any time, but such a texture that hath the power to produce such a sensation in us.
  • 17. Locke: primary qualities are always present, secondary qualities are highly mutable. 20. Pound an almond, and the clear white colour will be altered into a dirty one, and the sweet taste into an oily one. What real alteration can the beating of the pestle make in any body, but an alteration of the texture of it?
  • 18. Locke: Primary Qualities are True Resemblances 15. [Ideas of primary qualities are true resemblances – but secondary qualities are not]…the ideas of primary qualities of bodies are resemblances of them, and…do really exist in the bodies themselves, but the ideas produced in us by these secondary qualities have no resemblance to the bodies themselves. They are, in the bodies we denominate from them, only a power to produce those sensations in us: and what is sweet, blue, or warm in idea, is but the certain bulk, figure, and motion of the insensible parts…
  • 19. Locke: perceptual variation explained 16 Examples. Flame is denominated hot and light; snow, white and cold; and manna [sugar from plant sap] white and sweet...And yet…the same fire that, at one distance produces in us the sensation of warmth, does, at a nearer approach, produce in us the far different sensation of pain. Is this idea of warmth actually in the fire or is this idea of pain in the fire? The fire produces these ideas only through the bulk, figure, number, and motion of its parts…
  • 20. Writing task: Primary Versus Secondary 22. …I hope I shall be pardoned this little excursion into science. But now I have distinguished the primary and real qualities of bodies, which are always in them (viz. solidity, extension, figure, number, and motion, or rest…) from those secondary and imputed qualities, which are but the powers of several combinations of those primary ones. [So now] we know which ideas are, and which are not, resemblances of something really existing. Explain the difference between primary and secondary qualities, and the relationship between them.
  • 21. Arguments for the primary/secondary distinction 1 Locke’s view protects the objectivity of the external world and explains perceptual variation • Primary qualities capture those features of experience that provide us with a conception of an objective world, distinct from the merely subjective series of observer-relative sensations. • We are subject to illusion and perceptual variation with respect to secondary qualities, but not with primary qualities. Locke’s example: a cold hand and a hot hand dunked into the same water feel subjectively different sensations. • Temperature is motion, so the primary qualities of the water are invariant. • The same primary qualities cause different secondary qualities because of their interaction with the perceiver. • Locke’s account has both objective reality and also saves the appearances we perceive.
  • 22. • Locke’s claim that more basic physical qualities cause perceiver- dependent qualities maps neatly to the emerging scientific world- view. • Science, then as now, distinguishes explanatorily basic primary qualities from less fundamental secondary qualities. • C17 ‘corpuscularian hypothesis’ posited primary qualities as characterizing the fundamental nature of matter. • The hard physical sciences these days deal only with the measurable physical qualities of objects, the primary qualities • present-day science has incredible explanatory power because of the prevalence of the ‘atomic model’ of matter, even if we have revised our notion of ‘solidity’ • Science also causally explains what it actually means for objects to have secondary properties, and does so in terms solely of primary properties. Arguments for the primary/secondary distinction 2 Locke’s view fits neatly with the scientific worldview
  • 23. Issues with Locke’s account 1 Locke’s picture of secondary qualities seems inconsistent. • He claims that secondary properties are qualities in objects that cause ideas in our minds. • These qualities are relational properties that arise in our minds because of certain arrangements of primary qualities. They exist outside our minds. • Yet we cannot think of e.g. colour as ‘in’ objects (the porphyry example shows that colour is not in the stone itself) • Secondary properties such as colours are in fact effects on us. • So secondary qualities, as effects, are in our minds only. They are ideas. (And variable ones: think of perceptual variation…) • But Locke has, earlier, argued that ideas (=effects of qualities) and qualities (=causes of ideas) aren’t the same. • Are secondary qualities ideas or qualities? Locke’s account could be said to blur the distinction…
  • 24. Issues with Locke’s account 2 Primary qualities are not distinguishable from secondary ones • Locke claims that – mind-independent qualities cause mind-dependent qualities, – but we perceive both kinds of qualities simultaneously. • Yet how do we perceive primary qualities such as shape, motion, solidity and size? – Could we not argue (Berkeley!) that these mind-independent qualities are in fact only perceived through secondary qualities?(shape, motion etc are derived from colour etc) – Hence, if mind-independent qualities can only be known through mind-dependent ones, their existence and their correct resemblance to underlying physical objects cannot demonstrated. – Locke’s account merely buries issues of existence and resemblance – it does not explain them.
  • 25. Last bit of Indirect Realism syllabus There are problems arising from the view that mind- dependent objects represent mind-independent objects and are caused by mind-independent objects.
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