1. How does direct realism lead to indirect realism
Criticisms of direct realism (hallucination, time lag, perceptual variation and illusion) are also
supporting arguments for indirect realism
2. What is indirect realism
Indirect realism is a realist theory which claims that the immediate objects of perception are sense
data. This sense data is caused by, and represents, the mind independent external world.
3. What is indirect perception
According to indirect realism, physical objects are perceived indirectly, via sense data i.e. mental
images that represent physical objects. So, us perceiving sense data immediately allows us to
perceive physical objects indirectly.
4. What is non veridical perception
A form of perception which does not coincide with reality, i.e. the mind independent objects of the
external world. It includes illusions, perceptual variation, time lag and hallucinations.
5. What are sense data
Sense data are mental images that represent the mind independent world. They are the content of
your sensations.
6. Explain how perception works according to an indirect realist
Indirect realism claims the immediate objects of perception are sense data. This sense data
represents, and is caused by, the mind independent external world. It claims there are three
elements to perception: the perceiver, the objects they perceive and also the sense data. Indirect
realists argue perception is a source of knowledge because sense experience can cause and justify
our true beliefs about the mind independent world. They claim the mind independent world causes
us to produce sense data, which we perceive directly. This causes us to form beliefs about what
exists.
7. Outline Locke’s primary and secondary qualities distinction
Locke’s distinction between primary and secondary qualities relates closely to sense data. He argues
primary qualities are inherent in the object itself. They are objective. For example, when I look at a
tree, my sense data of its size, shape and motion correspond accurately with the object itself.
Secondary qualities are the powers of an object to cause sensations in humans. They are subjective.
So when I look at a tree, my sense data of its colour, taste and smell are specific to me. This
distinction can be used to support indirect realism as it explains the difference between reality
(primary qualities) and sense data (secondary qualities).
8. Outline the argument from hallucination for indirect realism
Hallucinations are a form of non veridical perception (you perceive something which isn’t actually
there e.g. a flying pig). Often a person is unable to distinguish their hallucination from veridical
perception – the two experiences are subjectively indistinguishable. But if they are subjectively
indistinguishable then the person must be aware of the same thing in both cases. Since what they
would be aware of in a hallucination is in the mind, what they're aware of in veridical perception
, must also be in the mind. Therefore we must perceive the sense data directly during veridical
perception, and the external world indirectly. Therefore indirect realism is true.
9. Outline the argument from perceptual variation for indirect realism
Bertrand Russell uses the example of a table to illustrate this criticism. He notes that from directly
overhead a table appears to look rectangular, but from further away it may seem kite shaped. The
issue is that the table cannot be both shapes at the same time – the properties of the table itself are
not varying. So, in at least one case I must not be perceiving the table exactly as it is. This example
highlights the differences in our perception of the table and the table itself. If we truly perceived the
external world directly, the table’s appearance would be constant, but we don’t. Therefore there
must be an intermediary to explain the differences between perception and reality. Russell, an
indirect realist, concludes that the immediate objects of perception are sense data and so we do not
experience the world directly.
10. Outline the argument from time lag for indirect realism
This argument begins by pointing out that it takes around eight minutes for light from the Sun to
reach the Earth. So, when we look at the Sun, we are not seeing it as it is now but instead as it was
eight minutes ago. Russell argues out if the Sun had ceased to exist within the last eight minutes, we
wouldn’t yet be aware of this. But if what we’re currently seeing may no longer exist, then we
cannot really be seeing it. We must be perceiving something else – sense data caused by the Sun
instead of the Sun itself. This is true of objects on Earth too, except the time lag is much shorter.
Therefore, we can conclude that the immediate objects of perception are sense data, and our
perception of the mind independent external world is indirect.
11. Outline the argument from illusion for indirect realism
This argument begins by noticing that a pencil half immersed in a glass of water will look crooked,
when we can be confident that the pencil itself isn’t. So the way the world appears to us must not be
the way the world actually is. From this we must conclude that the immediate objects of perception
cannot be the mind independent external world, since how could reality be different to our
perception of it? So what we are aware of (the bent pencil) and what is real (the straight pencil) are
distinct. Therefore we must be perceiving sense data, as this represents and is cause by physical
objects.
12. Explain the issue of scepticism as a criticism of indirect realism
A criticism of indirect realism is that it leads to scepticism about the nature and existence of the
external world. According to IR we are directly aware of sense data and must infer the existence of
objects beyond the mind (in the mind independent external world). This leads to the problem of if
we only experience sense data and never the objects themselves, how can we know anything about
the external world or even if there is one? It is conceivable that I am simply a brain in a vat, or there
is a Cartesian demon deceiving me. We can't get beyond the veil of perception (sense data) to access
the external world behind it. Inferring from sense data is not sufficient enough to provide us with
knowledge that the mind independent world exists.
13. Explain the involuntary nature of our experience as a response to scepticism
Locke’s response to the problem of scepticism involves pointing out that we are not in control of our
sense data. Locke’s example is ‘once letters have been put onto paper, I have no choice about
afterwards seeing them as they are,’ meaning we have perceptual experiences whether we want
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