1. Criticisms of Indirect Realism
Understand the main criticisms of Indirect Realism.
Explain how they undermine the argument
Consider the validity of the responses to the criticisms.

2. Fill in the Gaps

3. Fill in the Gaps Indirect realism
Indirect realism claims that we perceive ____ _____which are ____-independent, but we do so via, or in virtue of, perceiving mind-dependent _____-____ that are caused by and represent physical objects. We perceive sense-data _______, and physical objects indirectly.

4. Fill in the Gaps Indirect realism
Indirect realism claims that we perceive physical objects which are mind-independent, but we do so via, or in virtue of, perceiving mind-dependent sense-data that are caused by and represent physical objects. We perceive sense-data immediately, and physical objects indirectly.

5. Argument from Perceptual Variation for Indirect Realism.
1 There are ______ in perception.
2 Our perception varies without corresponding changes in the physical object we perceive. (For instance, the desk remains rectangular, even as the way it looks to me changes as I look at it from different angles.)
3 Therefore, the ______ physical objects have and the properties they appear to have are not identical.
4 Therefore, what we are immediately aware of in ______ is not exactly the same as what exists independently of our _____.
5 Therefore, we do not _____ physical objects directly.

6. Argument from Perceptual Variation for Indirect Realism.
1 There are variations in perception.
2 Our perception varies without corresponding changes in the physical object we perceive. (For instance, the desk remains rectangular, even as the way it looks to me changes as I look at it from different angles.)
3 Therefore, the properties physical objects have and the properties they appear to have are not identical.
4 Therefore, what we are immediately aware of in perception is not exactly the same as what exists independently of our minds.
5 Therefore, we do not perceive physical objects directly.

7. Argument from Illusion and Hallucination for Indirect Realism
There are perceptual experiences, such as ______ and ________, in which what we experience are not the properties of physical objects.
When we perceive something having some property F, then there is something that has this______.
In such cases, given that what we perceive is not the way the world is, what we perceive are sense-data.
Such cases are subjectively ___________ from veridical perception.
When two perceptual experiences are subjectively indistinguishable, they are perceptual experiences of the same thing. (This claim is the best hypothesis, given (4).)
Therefore, we ______ perceive sense-data (not just in cases in which what we perceive is not the way the world is).
Nevertheless, except in hallucinations, it still makes sense to say we perceive the world. In cases of both veridical perception and illusion, the sense-data we perceive are _____ by and ______ physical objects. This representation can be accurate or inaccurate in certain ways – physical objects may be as they appear to us, or they may differ in certain ways.
Therefore, we perceive physical objects _______, via sense-data.

8. Argument from Illusion and Hallucination for Indirect Realism
There are perceptual experiences, such as illusions and hallucinations, in which what we experience are not the properties of physical objects.
When we perceive something having some property F, then there is something that has this property.
In such cases, given that what we perceive is not the way the world is, what we perceive are sense-data.
Such cases are subjectively indistinguishable from veridical perception.
When two perceptual experiences are subjectively indistinguishable, they are perceptual experiences of the same thing. (This claim is the best hypothesis, given (4).)
Therefore, we always perceive sense-data (not just in cases in which what we perceive is not the way the world is).
Nevertheless, except in hallucinations, it still makes sense to say we perceive the world. In cases of both veridical perception and illusion, the sense-data we perceive are caused by and represent physical objects. This representation can be accurate or inaccurate in certain ways – physical objects may be as they appear to us, or they may differ in certain ways.
Therefore, we perceive physical objects indirectly, via sense-data.

9. Criticism #1 Skepticism about the External World
Russell's problem… (The Problems of Philosophy CH2)
If what we perceive directly are sense-data, then all we know about are sense-data. We believe that ‘behind’ the sense-data there is a real physical object, that physical objects cause our sense-data. But how can we know this? To know that physical objects cause sense-data, we first have to know that physical objects exist. But the only access we have to physical objects is through our sense-data.

10. #1 Criticism What do you think?
Because we directly perceive sense-data, we cannot know that a world of physical objects – a world external to and independent of our minds – exists. Scepticism is the view that we cannot know, or cannot show that we know, a particular claim, in this case the claim that physical objects exist. Indirect realism leads to scepticism about the existence of the external world.

11. Criticism #1
Again, if we accept IDR, then what we perceive directly is sense-data as this is all we know about. However, IDR believes that behind the sense data there are real physical objects that cause our sense data. But how can we truly know this? To know that physical objects cause sense-data, we first need to know whether physical objects exist or not.
Even if we can show that our sense-data are caused by something that exists independently of us and our minds, how can we establish the thing that causes it?
Russell raises this problem in Chapter 2, The Problems of Philosophy:
‘Granted that we are certain of our own sense-data, have we any reason for regarding them as signs of the existence of something else, which we can call the physical object?

12. Tweet In less than 140 characters tweet Russell's argument against IDR
#epicfail #mrchurchill’scoolnewteachingmethods

13. Responses to #1
Russell offers two responses, both appealing to how we should explain what we do know. The first is this: the fact that sense-data are private means that no two people actually ever perceive the same thing, unless we can say that there are physical objects that they both perceive (indirectly). People perceive the same thing. They have very similar sense-data if they are at the same place and time. The best explanation of this is that there are physical objects causing their sense-data.

14. Why do you think Russell quickly dismisses this?

15. Because…
Russell rejects this argument because it assumes something that we can’t know: that there are other people, and that they have sense-data, and that their sense-data are similar to mine. To assume that there are other people is to assume that there are physical objects, since people are physical objects. But the question was how, from my sense-data, do I know that there are physical objects? In answering that question, I can’t assume that there are physical objects (such as other people) – that’s begging the question!

16. Begging the question?

17. 2nd Response from Russell
Either physical objects exist and cause my sense-data or physical objects do not exist and so do not cause my sense-data.
I can’t prove either claim is true or false.
Therefore, I have to treat them as hypotheses. (A hypothesis is a proposal that needs to be confirmed or rejected by reasoning or experience.)
The hypothesis that physical objects exist and cause my sense-data is better.
Therefore, physical objects exist and cause my sense-data.

18. Premise 4
“The hypothesis that physical objects exist and cause my sense-data is better.”
So how does this work?

19. Russell’s qualification
Statement 4 can be verified by testing a hypothesis to see whether it explains why my experience is the way it is. For example: ‘I see a cat first in a corner of the room and then later on the sofa, then if the cat is a physical object, it travelled from the corner to the sofa when I wasn’t looking. If there is no cat apart from what I see in my sense-data, then the cat does not exist when I don’t see it.

20. It springs into existence first in the corner, and then later on the sofa. Nothing connects my two perceptions. But that’s incredibly puzzling – indeed, it is no explanation at all of why my sense-data are the way they are! So the hypothesis that there is a physical object – the cat – that causes what I see is the best explanation of my sense-data.’ (Lacewing p.41)

21. Criticism #2 it leads to scepticism about the ‘nature’ of the external world
If we accept IDR, then all we know about and are aware of is sense data i.e. a representation of reality in my mind. However, this means I cannot have immediate access to the external real world and reality. This leads to the question – ‘But if I cannot have immediate access to reality, then how am I to determine how accurate the representation of it is in my mind?’

22. Criticism #2
We seem to have no way of checking whether our sense-data accurately represents the world – and so, no way of knowing that they do.

23. Analogy of the Cinema
Imagine that you have spent your whole life locked inside a cinema. Inside the cinema, films are continually rolling, telling you about the outside world – but you are never able to check the accuracy of these films for yourself. In fact, the films are completely accurate, and it never occurs to you to doubt their accuracy. Given that this is so, is it fair to say that, through them, you know what the world is like outside the cinema?
Some would say that, if indirect realism is true, we are like the character described in the analogy above. You are trapped in a cinema with no way of telling whether the images projected are genuine pictures of the outside world.

24. Explain the cinema analogy and how it criticises ‘Indirect Realism’ (9)

25. But Locke…?
Does Locke’s primary and secondary qualities distinction not solve matters?
If I cannot have immediate access to reality, how can I determine how accurate the representation of it is in my mind?  If we can doubt that secondary qualities resemble reality, how does it prevent us having the same doubt with primary qualities?

26. But Locke…?
Locke relies on ‘the corpuscular physics’ to defend this distinction. i.e. universe is made up of imperceptible atoms that possess the properties of size, shape etc and secondary qualities are the microstructures of these particles which cause sensations in us.

27. However, if the link between secondary qualities and reality is not one of resemblance, how can we be certain of what causes us to perceive these secondary qualities? Therefore questions arise of how sure we can be that the sense data we perceive of objects resemble their sense data. To be certain we would need a ‘God’s-eye view’ of the world, which is impossible.

28. Hume, Locke and Russell
Locke and Russell are empiricists and so argue that all knowledge of the world can only come to us through experience. However, since we only have immediate and certain knowledge of sense data one cannot experience the relationship between sense data and reality. Hume argues a similar point:
It is a question of fact, whether the perceptions of the senses be produced by external objects, resembling them: how shall this question be determined? By experience surely; as all other questions of a like nature. But here experience is, and must be entirely silent. The mind has never anything present to it but the perceptions, and cannot possibly reach any experience of their connexion with objects. The supposition of such a connexion is, therefore, without any foundation in reasoning.
Hume’s Enquiry, I, xii, part 1, paragraph 119
This leads onto the sceptical worry which is outlined in the concept: ‘veil of perception’.

29. Veil of Perception The veil of perception:
Indirect realism risks making the external world inaccessible to us.
It is as though an impenetrable veil has dropped down between us and the world  we only have access to our representations.

30. Two Defenses 1.We would not survive
If the world we perceive did not match the external world, then we would have been unable to hunt & gather. The human species would have died out years ago.
Therefore the correspondence between the two worlds (i.e. the external world and the world as we perceive it) must be sound.
However it still doesn’t tell us how accurate our perception is………. Different species have different ways of perceiving the external world.
2. Appealing to the testimony of other people
If everyone perceives the world roughly as we do then we have some evidence that the world is in fact how it appears.
However, the perception of second observer will have the same difficulties as me.
Example of the matrix – useless for people in the matrix to appeal to fellow matrix citizens.

31. Response 1#
See earlier notes on Locke and Primary and Secondary qualities.

32. Response 2# Sense Data is the way
Russell calls what we are immediately aware of within the mind a ‘private space’ that consists of sense data.
The shapes we perceive and the relative distances between the objects will vary between different individuals’ private spaces, and within my own as I walk around the table.
For objects in physical space to cause our sense data we must exist in physical space as well.
The relative positions of physical objects in space in the real external world – left, right, just in front etc – ‘correspond to’ the relative positions of sense-data in apparent space. I.e. it will take me longer to walk through physical space to the corner shop that appears further away than the corner shop that appears closer.

33. Therefore
Therefore there is a correspondence between my private space (of sense data) and physical space. From this we can make reliable judgements about ‘the shapes and relative positions’ of real physical, mind-independent objects.

34. The Time Argument : Russell
Russell also distinguishes between private and public time: ‘real’ time is distinct from our ‘feeling of duration’.
We are immediately aware of our own feeling of how long something took i.e. how time appears subjectively to pass. For instance, if we are really enjoying a philosophy lesson, the hour lesson will seem to pass quickly!
We can never know the ‘real time’ in which physical objects exist but we can know about ‘relative’ times i.e. whether something comes before or after something else.
Therefore we can have an idea of the nature of the external world through the relation between real time and relative time.

35. Problems arising from the view that mind-dependent objects represent mind-independent objects and are caused by mind-independent objects.
These arguments all require that our minds are causally affected by physical objects i.e. I perceive a Granny Smith apple (the mind-independent object & its primary qualities) through sense data (secondary qualities). The physical objects causally affect our sense organs that consequently affect our brains. But, ‘how does what happens in our brains causally affect our conscious perception?’ How can something physical cause an idea in our brains? This is a perennial question for IDR (& DR too) and whether it is a valid theory of perception. 
Berkeley’s idealism attempts to dismiss this criticism through rejecting realism and adopting idealism.