knowledge from perception Flashcards
what does knowledge from perception try to explain?
how we can acquire knowledge from experience, i.e, a posteriori
what is direct realism?
the view that:
-The external world exists independently of the mind (hence, realism)
-And we perceive the external world directly (hence, direct)
what are the problems for direct realism?
diferences in perceptual variation, arguments from illusion, argument from hallucination and the time lag argument
explain Bertrand Russell’s argument from perceptual variation?
Russell also talks about the shape of a table. from directly overhead, it may appear to be rectangular. but from a few metres away it may look kite-shaped. it can’t be both shapes. the table may also have white spots dependent on who and how you look at it but it cant be brown and white, so somebody is not perceiving the table directly as it is.
these examples highlight differences in our perception of the table and the table itself. however, according to direct realism, there should be no such differences between perception and reality.
what is a possible response to the argument from perceptual variation?
direct realism can respond by refining the theory and introducing the idea of relational properties. a relational property is one that varies in relation to something else. we could say that the table has the (mind-independent) relational property of appearing kite-shaped relative to certain perceivers, whilst simultaneously having the (mind-independent) relational property of appearing square-shaped to other perceivers
explain the argument from illusion?
direct realism says that we perceive the external world directly as it is. but if this is true, how is it that reality (i.e. the external world) can be different to our perception of it? for example, when a pencil is placed in a glass of water, it can look crooked. but it isn’t really crooked. If direct realism is true, the external world would be exactly as we perceive it. however, in the case of illusions, there is an obvious difference between our perception and reality.
what is the response to argument from illusion?
the direct realist could reply that the pencil has the relational property of looking crooked to certain perceivers
explain the argument from hallucination?
direct realism says that when we perceive something, we are perceiving something in the external world (directly). but during hallucinations – perhaps as a result of being ill or taking drugs – we perceive things that aren’t even there. so what is causing these perceptions? It can’t be the external world – at least not directly – because there is no external object being perceived at all
explain the time lag argument?
it takes approximately 8 minutes for light to reach earth. so, when you look at the sun, you are seeing it as it was 8 minutes ago – i.e. there is a difference between the sun itself and your perception of it. In other words, you are not perceiving the sun directly.
what is a possible repsonse to the time lag argument?
the direct realist can argue that this response confuses what we perceive with how we perceive it. yes, we perceive objects via light and sound waves and, yes, it takes time for these light and sound waves to travel through space. but what we are perceiving is still a mind-independent object (it’s not sense data or some other mind-dependent thing) – it’s just we are perceiving the object as it was moments ago rather than how it is now.
what is indirect realism?
the view that:
-The external world exists independently of the mind (hence, realism)
-But we perceive the external world indirectly, via sense data (hence, indirect)
what does indirect realism say sense data is?
-indirect realism says the immediate object of perception is sense data. This sense data is caused by, and represents, the mind-independent external world. they claim that what we really perceive is sense data.
-sense data can be described as the content of perceptual experience.
-it’s not a physical thing, it exists in the mind. however, sense data is said to be caused by and represent mind-independent physical objects (see diagram above).
-sense data is private. no one else can experience your sense data.
-this avoids the problems with direct realism described above. for example, differences in perceptual variation can be explained by differences in sense data. the object itself stays the same throughout even if the sense data changes.
what is a primary quality?
properties that are inherent in the object itself, they are objective, e.g, size, shape, motion
what are secondary qualities?
powers of an object to cause sensations in humans, they are subjective, e.g, colour, taste, smell, feel
what example does Locke use
porphyry – a red and white stone. Locke says that when you prevent light from reaching porphyry, “its colours vanish”. however, the primary qualities – size, shape, etc. – remain.
how does the distinction between primary and secondary qualities support indirect realism?
the distinction explains the difference between reality (primary qualities) and our perception of it (secondary qualities).
what is a problem for indirect realism?
Berkeley
Berkeley argues that mind independent objects are totally different to sense data, he questions how it’s possible for mind-dependent sense data to resemble so-called mind-independent objects in any way. how can the properties of sense data be like the properties of mind-independent objects?
sense data changes, but the mind-independent object doesn’t. We say that a table is square, but how can my sense data be square? These major differences between sense data and mind-independent objects undermine the indirect realist claim that sense data is caused by and resembles mind-independent objects.
explain scepticism and the veil of perception
If we only perceive sense data, and not the object itself, how can we know anything about the external world? There is no way of telling if the sense data is an accurate representation of the external world, or if there is one at all. So, how can indirect realism justify its claim that there is a mind-independent external world that causes sense data if we never actually perceive the mind-independent external world itself?
how did indirect realist repies to scepticism?
Russell’s reply: External world is the best hypothesis; Bertrand Russell, an indirect realist, concedes that there is no way we can conclusively defeat this sceptical argument and prove the existence of the external world. So, instead, we must treat the external world as a hypothesis.
