The Big Picture. Part One: The Nature of Knowledge Weeks 2-3: What is Knowledge? Week 4: What is Justification?

Transcription

1 The Big Picture Part One: The Nature of Knowledge Weeks 2-3: What is Knowledge? A: Its somehow related to justification Week 4: What is Justification? A: It requires epistemically basic beliefs? Part Two: Ways of Knowing Weeks 5-7: Perception Means of acquiring empirical knowledge Weeks 8-9: A Priori Reasoning Means of acquiring non-empirical knowledge

2 7. Overview The Argument from Illusion Illusions Responses

3 The Argument from Illusion 1) Physical objects sometimes appear other than they really are Physical object is F, but appears G E.g. a tilted penny is round, but appears ellipical

4 The Argument from Illusion 2) When something appears to have a certain property, there is something that the subject is aware of a sense-datum that really has that property ( The Phenomenal Principle ) E.g. if a tilted penny appears elliptical, then there is something that really is elliptical Plausibly, perceiving (being aware of, etc.) is a relation, and relations have relata: perceiver and perceived. If so, perceives a success term (cf. knows, week 1). (Note: singular sense-datum, plural sense-data.)

5 The Argument from Illusion 3) Sense-data are distinct from physical objects Physical object is F, sense-datum is G E.g. penny is round, sense-datum is elliptical Leibniz s Law: if a and b are identical, then everything that is true of a is true of b a = b ( F)(Fa Fb) 4) Therefore, in cases of illusion we are not aware of physical objects, but sense-data

6 The Argument from Illusion Generalising: 5) Illusory perceptual experiences are at least in principle indistinguishable from other types of perceptual experience 6) If illusory perceptual experiences are indistinguishable from other types of perceptual experience, then these experiences are of the same fundamental kind 7) Therefore, we are never (directly) aware of physical objects, but only sense-data

7 Subjective Illusions Blurred vision: remove glasses, get drunk Double Vision: move fingers close to eyes, gently(!) press side of eyeball Colour-blindness Jaundice(?)

8 After-Images Subjective Illusions

9 Subjective Illusions(?) Neon Colour Spreading

10 Environmental Illusions The Muller-Lyer Illusion

11 Environmental Illusions The Muller-Lyer Illusion

12 Environmental Illusions Bent Stick in Water

13 Environmental Illusions Shape Constancy Illusion

14 Environmental Illusions Size Constancy Illusion

15 Environmental Illusions Size Constancy Illusion

16 Environmental Illusions Colour Constancy Illusion Part of white square in shadow appears different to part of white square that is directly illuminated

17 Environmental Illusions Colour Constancy Illusion Part of white square in shadow appears different to part of white square that is directly illuminated Note also, that square A is the same colour as square B!

18 Environmental Illusions Lotto-Purves Cube

19 Hallucinations Drugs Evil Scientist Dreams? Note: the Argument from Hallucination is slightly different to the Argument from Illusion. Can you think how it might go?

20 The Argument from Illusion 1) Physical objects sometimes appear other than they really are 2) When something appears to have a certain property, there is something that the subject is aware of a sense-datum that really has that property ( The Phenomenal Principle ) 3) Sense-data are distinct from physical objects 4) Therefore, in cases of illusion we are not aware of physical objects, but sense-data 5) Illusory perceptual experiences are at least in principle indistinguishable from other types of perceptual experience 6) If illusory perceptual experiences are indistinguishable from other types of perceptual experience, then these experiences are of the same fundamental kind 7) Therefore, we are never aware of physical objects, but only sense-data

21 Responses: Premiss 1 1) Physical objects sometimes appear other than they really are In some sense, tilted pennies do not appear elliptical: they appear to be round pennies tilted in space. Constant properties (e.g. shape, size, colour) are: Phenomenologically salient Epistemologically important Constancy depends on awareness of contextual cues: orientation (shape), distance (size), illumination (colour)

22 Responses: Premiss 1 Some Questions Do tilted pennies appear round in the phenomenal sense of appears? Do we literally perceive tilted pennies to be round? Or do we merely believe that they are round? Despite constancy, there is some difference between perceiving a penny face on and tilted in space. What? Constancy fails if contextual cues are removed (cf. monsters in the tunnel) What about subjective illusions and hallucinations?

23 Responses: Premiss 2 2) When something appears to have a certain property, there is something that the subject is aware of a sense-datum that really has that property ( The Phenomenal Principle ) Premiss rejected by intentionalists (week 6). Perceptual experience is representational: it does not imply the existence of what it is a representation of Compare belief: I believe that Father Christmas is fat does not imply that Father Christmas exists

24 Responses: Premiss 5 5) Illusory perceptual experiences are at least in principle indistinguishable from other types of perceptual experience Austin (p. 80): I may have the experience (dubbed delusive presumably) of dreaming that I am being presented to the Pope. Could it seriously be suggested that having this dream is qualitatively indistinguishable from actually being presented to the Pope? Cf. Berkeley: dreams are less coherent, and have less force and vivacity than waking experiences (Principles of Human Knowledge, 30, 33, 41)

25 Responses: Premiss 5 But are illusory perceptual experiences at least in principle indistinguishable from other types of perceptual experience? Two types of experience can have the same proximate cause in the brain. Plausibly, two experiences with the same proximate cause could be indistinguishable.

26 Responses: Premiss 6 6) If illusory perceptual experiences are indistinguishable from other types of perceptual experience, then these experiences are of the same fundamental kind Austin (p. 81): If I am told that a lemon is generically different from a piece of soap, do I expect that no piece of soap could look just like a lemon? Why should I? Premiss rejected by disjunctivists (week 7) Illusion/hallucination and veridical perception are fundamentally different: no highest common factor

27 Responses: Accept? 7) Therefore, we are never aware of physical objects, but only sense-data If we accept the conclusion, then we are committed to the sense-datum theory of perception. See lecture 8

28 References Online Illusions The Argument from Illusion T. Crane, The Problem of Perception, The Stanford Encyclopedia of Philosophy, H. Robinson, Perception (London: Routledge, 1994) H.H. Price, Perception (London: Methuen, 1932), Chapter 1