perception as a source of knowledge

direct realism (5 m)

• immediate objects of perception are mind-independent objects and their properties

• two elements - perceiver and object perceived

• no mediator - perceived immediately and directly

• senses detect properties (e.g. colour, shape) - inherent in objects themselves

• object and properties continue to exist when unperceived

sense data (3 m)

• content of perceptual experience

• private - exists in mind of an individual

• caused by/represents mind-independent objects

argument from perceptual variation (5 m)

• appearance of physical objects varies depending on conditions

• russell (problems of philosophy) - table appears white where light reflects but brown otherwise - apparent shape changes when viewed from different angles

• possible for our perception to vary without changes to properties of the object itself

• apparent properties are not the same as real properties - so dr is false

• immediate objects = sense data - used to infer existence of objects

dr response to perceptual variation (5 m)

• relational properties - vary in relation to something else

• e.g. being to the left or right of something is a real property - but is dependent on position of the objects and of the perceiver

• russell’s table - has the property of appearing kite-shaped relative to certain perceivers

• rps belong to the object and are directly and immediately perceived - even though they can change

• therefore not necessary to introduce sense data as a mediator - objects are still directly perceived

argument from illusion (5 m)

• objects can appear to have particular properties that they do not - e.g. a straight straw appears bent when placed in glass of water

• perceiver is directly aware of this apparent property - a bent-looking straw

• object does not have this property in reality - real straw is not bent

• what the perceiver is directly aware of (bent straw) and what is real (straight straw) are distinct

• therefore we do not perceive objects directly - so dr is false

dr response to illusion (5 m)

• i am not directly aware of anything distinct from the physical object - appearance of the straw is not a thing in itself

• i am directly aware of the real straw - but it appears bent because of the circumstances (light travelling through two different mediums)

• i am directly and accurately perceiving the refraction of light as it travels through the glass of water

• drs do not have to assume that objects appear exactly as they are

• can appear differently because of how they relate to the perceiver - not necessary to introduce sense data as mediator

argument from hallucination (5 m)

• hallucination = i perceive something that exists only in my mind - mind-dependent sense data

• can be subjectively indistinguishable from veridical perceptions

• if this is the case i must be aware of the same thing in both cases

• so what i am directly aware of during veridical perception must also be in the mind - sense data/ideas

• therefore we perceive the world indirectly - so dr is false

response to hallucination (5 m)

• hallucinations and veridical perception being subjectively indistinguishable does not mean they are the same phenomenon in reality

• vp caused by physical object impacting on sense organs

• hallucinations caused by some malfunction in the brain

• they can be indistinguishable to the perceiver - still distinct phenomena

• hallucinations occur in mind - does not follow that vp involves a purely mental element (sense data)

time-lag argument (5 m)

• russell (problems of philosophy) - light from sun takes 8 mins to travel to earth

• not seeing the sun as it is now but as it was 8 mins ago - could have ceased to exist in last 8 mins but would not know yet

• if what you are perceiving may no longer exist, you cannot be perceiving it directly - must be sense data caused by sun’s light impacting on sense organs

• true of distant objects - also true of close objects - time-lag is just far shorter

• we are directly aware of appearances/sense data and not objects themselves - so dr is false

response to time-lag (5 m)

• dr does not need to claim that the moment at which we perceive an object must be simultaneous with the object perceived

• it is undeniably true that light mediates between us and objects (such as the sun) and that there are physiological processes that must take place in our bodies before we become aware of an object

• these processes of mediation are not sense data - it is not implied that we must introduce sense data to infer the existence objects

• time-lag does not mean that we perceive objects indirectly, just that we perceive them directly as they were

• therefore once we become aware of an object, we are immediately aware of the object itself

indirect realism (5 m)

• immediate objects of perception are mind-dependent objects and their properties - caused by (and represent) mind-independent objects

• three elements - perceiver, real objects, appearance of objects to the perceiver

• directly aware of sense data or ideas - representations of reality used to infer the existence and nature of physical objects

locke’s primary/secondary quality distinction (5 m)

• quality = the power to produce an idea in our mind

• primary qualities (size, shape, motion) are intrinstic - utterly inseparable from object

  • if you continually divide an object (grain of wheat) the parts must retain pqs even when they are too small to be perceived

  • therefore pqs must exist mind-independently

• secondary qualities (colour, smell, taste) caused by primary qualities

  • when we pound an almond we merely change the shape (pq) of its parts, but the colour and taste (sq) also change - caused by change in pq

  • smell and taste disappear if we block our sense organs - not inherent qualities

  • therefore sqs are mind-dependent

locke’s perceptual variation (5 m)

• supports pq/sq distinction

• bucket of lukewarm water produces idea of cold to a warm hand, but idea of warmth to a cold hand

• the water cannot be cold and warm at the same time

• so the cold or warmth cannot be a mind-independent quality of the water

• therefore cold and warmth are mind-dependent sensations produced in the mind of the perceiver

issue of scepticism (5 m)

• ir - directly aware only of sense data - infer existence of mi objects

• senses can deceive us - can lead to scepticism about existence of an external world

• it is conceivable that sense data does not correspond with any material reality e.g. if i am a brain in a vat or there is a powerful cartesian demon deceiving me

• so the inference of the external world is not valid or sufficient for knowledge

• veil of perception - sense data acts as a veil between us and reality

• impossible to directly observe the external world - so we cannot be sure that it exists

involuntary nature of our experience (5 m)

• response to scepticism

• locke - we are not in control of our sense data

• when i open my eyes i receive certain sense data - not something i have any choice about

• as perception is not subject to my will, it cannot be caused by me

• therefore the source of my perceptions must be external

coherence of various kinds of experience (5 m)

• response to scepticism

• different senses seem to cohere with each other - locke - we see a fire and feel its heat

• cockburn - we learn to associate how objects feel when touched with how they appear e.g. if i recognise a die by touch i can predict how it will look

• i can predict what i will perceive next - if i close my eyes while writing i can predict the words that will appear when i open my eyes again

• locke accepts these are not deductively valid arguments - when we dream our senses are not subject to our will, but we do not say that dreams correspond with material reality - shows that inference of external mi objects is reasonable and best explanation of our experience

best hypothesis (5 m)

• response to scepticism

• russell - no deductive proof of nature of material reality is possible

• we have an instinctive belief in existence of material reality which corresponds with our sense data

• we should only reject such instinctive beliefs if they are shown to be incoherent

• if a cat is seen in one place, then appears in another, it is natural to believe the cat has moved while we were not looking - if the cat exists when we do not perceive it, its easy to infer that it becomes hungry between meals

• this belief in an external world does not seem to be contradictory - explains why our sense data appear in regular and predictable ways

• abductive reasoning - best explanation for our perception

berkeley’s likeness principle (5 m)

• attack on indirect realism - mind-dependent sense data/ideas are caused by (and represent) mind-independent objects

• if one thing x resembles another thing y, it must be like that thing - must have something in common

• an idea cannot resemble another thing which is not like it, and the mental is not like the physical

• mental ideas are not like physical objects

• therefore ideas cannot be said to resemble objects

berkeley’s attack on primary/secondary quality distinction (5 m)

• locke - pqs inherent in object - sqs caused by pqs and have power to cause sensations in our minds

• agrees it is impossible to imagine an object without pqs

• however it is also impossible to imagine an object with ONLY pqs - if we try to imagine an object without colours we will likely imagine it as black, white or transparent (so the colour of the object behind it)

• so our ideas of sqs of an object cannot be separated from those of its pqs

• it follows that they must exist together

• irs accept that our ideas of sqs are mind-dependent

• therefore it follows that our ideas of pqs are also mind-dependent

berkeley’s perceptual variation (5 m)

• also attack on primary/secondary quality distinction

• what looks small to us will appear big to a small animal

  • but an object cannot be small and big at the same time

  • therefore size cannot be a property of material objects

• perceived shape of an object changes depending on angle from which the perceiver is looking at it

  • but an object cannot have different shapes at the same time

  • therefore shape cannot be a property of material objects

• therefore we cannot say that an object has one real size or shape independent of how we perceive it

• therefore pqs are also mind-dependent

berkeley’s idealism (5 m)

• all that exists are minds and their ideas - immediate objects of perception are mind-dependent objects

• what we can physical objects are simply collections of ideas - do not exist independently of being perceived

• ‘esse est percipi’ (to be is to be perceived)

• does not believe that objects exist only when perceived by finite human minds

• the universe is sustained in existence as it is always being perceived in the infinite mind of god - god directly causes our ideas

berkeley’s master argument (5 m)

• three dialogues between hylas and philonous - asks us to try to conceive of a tree which exists independent of any mind

• in doing so, the tree is being conceived by me

• as the tree is in my mind, it is impossible to conceive of a tree that is mind-independent

• this is the case for all objects - must be capable of being conceived in order to exist BUT we cannot conceive of a mind-independent object - as soon as we do, it becomes mind-dependent

• therefore mind-independent objects are impossible and realism is false

issue of solipsism (5 m)

• idealism - immediate objects are mind-independent objects - all that exists are minds and their ideas

• solipsism - view that my mind is the only thing that exists

• if berkeley is correct that mi objects are impossible - seems to imply that the world first appeared when i was born, will disappear when i die, and comes in and out of existence every time i blink

• if all i perceive are ideas, then i never perceive other minds - so i cannot be sure that any other minds (including the mind of god) exist at all

response to solipsism (5 m)

• introducing solipsism is a slippery slope argument - i can agree that the only things i experience are my ideas while still believing that other people experience theirs

• berkeley - god as the cause of our ideas

  • if all that exists are minds and their ideas, then my ideas must be caused by either an idea or a mind

  • my ideas cannot be caused by other ideas - they have no causal power

  • i can cause some ideas through imagination - but most are involuntary so cannot come from my mind

  • the involuntary ideas i experience must be caused by another mind

  • due to the complexity and regularity of my ideas, this other mind must be far greater than my own i.e. god

• if god’s mind exists then my mind is not the only thing that exists - so idealism does not lead to solipsism

argument from illusion and hallucination - idealism (5 m)

• idealism does not distinguish between appearance and reality

• however in the case of illusions, objects seem to have two inconsistent properties - a straw that looks bent in a glass of water feels straight if i reach in and touch it

• objects cannot have these two properties at the same time (cannot be both straight and bent) - it seems that one must correspond to reality (as it exists in god’s mind) and the other must be an appearance

• therefore there is a difference between appearance and reality - so idealism is false

• in the case of hallucinations i perceive an object which does not exist

• hallucinations are subjectively indistinguishable from other perceptions so it is impossible to distinguish between hallucination and reality (as it exists as an idea in god’s mind)

response to illusion and hallucination - idealism (5 m)

• berkeley - when subject to an illusion i am not mistaken about the actual ideas or sense data i perceive

• illusions and hallucinations are subjectively indistinguishable from other sense experiences - it cannot be said that i am wrong about what i perceive

• however we regard these perceptions as illusory because they lead us to make false inferences about what we will perceive next

• if i see the bent straw and believe that it will also feel bent - or i try to pick up an object i am hallucinating - i am making an error

issue with the role of god (5 m)

• b’s idealism - perceive collections of ideas which are directly caused by god

• claims that everything we perceive is in the mind of god

• it follows that the idea of pain exists in the mind of god - god suffers pain

• if god suffers pain then he is imperfect

• god is defined as a perfect being

• so b’s idealism leads to a contradiction

response to the role of god (5 m)

• implication that god experiences pain contradicts definition of god as a perfect being

• berkeley - while god knows what it is for us to suffer pain he does not suffer it himself

• humans suffer pain because it is caused in accordance with the laws of nature, which we cannot control

• however god is a purely spiritual being with no physical body - impossible to passively suffer from pain or any other sensation against his will