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Perception 2016 revision 2. indirect realism part 1
Definition, first set of problems
The Syllabus: Indirect Realism
• the immediate objects of perception are mind-
dependent objects that are caused by and represent
mind- independent objects.
• Issues, including:
– it leads to scepticism about the ‘existence’ of the external world (attacking
‘realism’) – responses to this (external world is the ‘best hypothesis’
(Russell); coherence of the various senses and lack of choice over our
– it leads to scepticism about the ‘nature’ of the external world (attacking
‘representative’) - responses (sense data tell us of ‘relations’ between
objects (Russell); the distinction between primary and secondary qualities
– problems arising from the view that mind-dependent objects represent
mind-independent objects and are caused by mind-independent objects.
• Indirect realism: the immediate objects of
perception are mind-dependent objects that
are caused by and represent mind-
• Indirect Realists: John Locke, Rene Descartes,
David Hume, Bertrand Russell etc
Descartes’ Indirect Realism
taken from ‘Meditation 3’ (1641)
To discover the nature of our ideas the better, and to discourse
of them intelligibly, it will be convenient to distinguish them, as
they are ideas or perceptions in our minds, and as they are
modifications of matter in the bodies that cause such
perceptions in us; that so we may not think (as perhaps usually is
done) that they are exactly the images and resemblances of
something inherent in the subject; most of those [of sensation]
being in the mind no more the likeness of Something existing
Whatsoever the mind perceives in itself, or is the immediate
object of perception, thought, or understanding, that I call idea;
and the power to produce any idea in our mind, I call the quality
of the subject wherein that power is.
Explain Descartes’ distinction between ideas and qualities
Locke’s Indirect Realism
taken from his ‘An Essay Concerning Human Understanding’ (1690)
8. [Ideas and Qualities] Whatsoever the mind perceives
in itself, or is the immediate object of perception,
thought, or understanding, that I call idea; and the power
to produce any idea in our mind, I call a quality of the
subject wherein that power is. Thus a snowball having the
power to produce in us the ideas of white, cold, and
round, as they are in the snowball, I call qualities; and as
they are sensations or perceptions in our understandings,
I call them ideas.
Explain Locke’s distinction between ideas and qualities.
Hume’s Indirect Realism
From ‘Enquiry concerning Human Understanding’, section 12 (1748)
It seems clear that we humans are naturally, instinctively inclined to trust our senses, and that without
any reasoning—indeed, almost before the use of reason—we take it that there is an external universe
that doesn’t depend on our perceiving it and would have existed if there had never been any perceiving
creatures or if we had all been annihilated. Even the animals are governed by a similar opinion, and
maintain this belief in external objects in all their thoughts, plans and actions.
It also seems clear that when men follow this blind and powerful instinct of nature they always suppose
that the very images that their senses present to them are the external objects that they perceive; it
never crosses their minds that sensory images are merely representations of external objects. This very
table that we see as white and feel as hard is believed to exist independently of our perception, and to
be something external to our mind, which perceives it. Our presence doesn’t bring it into existence, and
our absence doesn’t annihilate it. It stays in existence (we think), complete and unchanging,
independent of any facts about intelligent beings who perceive it or think about it.
But the slightest philosophy is enough to destroy this basic belief that all men have. For philosophy
teaches us that images (or perceptions) are the only things that can ever be present to the mind, and
that the senses serve only to bring these images before the mind and cannot put our minds into any
immediate relation with external objects. The table that we see seems to shrink as we move away from
it; but the real table that exists independently of us doesn’t alter; so what was present to the mind
wasn’t the real table but only an image of it. These are the obvious dictates of reason; and no-one who
thinks about it has ever doubted that when we say ‘this house’ and ‘that tree’ the things we are
referring to are nothing but perceptions in the mind—ﬂeeting copies or representations of other things
that are independent of us and don’t change. To that extent, then, reason compels us to contradict or
depart from the basic instincts of nature, and to adopt a new set of views about the evidence of our
Explain Hume’s view of our ‘basic belief’ and why it is that the ‘slightest philosophy’ destroys it.
Russell’s Indirect Realism: sense-data
From ‘The Problems of Philosophy’ (1912)
Take Russell to be explaining, pace Hume, what Hume then goes on to say…
‘Let us give the name of 'sense-data' to the things that are immediately known
in sensation: such things as colours, sounds, smells, hardnesses, roughnesses,
and so on. We shall give the name 'sensation' to the experience of being
immediately aware of these things. Thus, whenever we see a colour, we have a
sensation of the colour, but the colour itself is a sense-datum, not a sensation.
The colour is that of which we are immediately aware, and the awareness itself
is the sensation. It is plain that if we are to know anything about the table, it
must be by means of the sense-data--brown colour, oblong shape, smoothness,
etc. – which we associate with the table; but, for the reasons which have been
given, we cannot say that the table is the sense-data, or even that the sense-data
are directly properties of the table. Thus a problem arises as to the relation of
the sense-data to the real table, supposing there is such a thing.’
In other words, Russell uses the perceptual variation problem as an argument
for indirect realism, by (re-)introducing the notion of sense-data.
The Qualities of Sense-Data
1. Sense-data are purely mental objects. Seemings. Appearances.
The content of your experience. The ‘Raw Feel’ of the world as it
appears to you. They are only as they seem or appear. They have
no further or deeper reality.
– So if our knowledge of physical objects is intermediated by sense-data, objects can
appear differently from how they really are, and perceptions can vary between
individuals, and illusions, hallucinations etc. can be explained away.
2. Sense-data, as mental objects, only exist while they are being
experienced. In contrast, physical objects exist when no one
3. Sense-data, as mental objects, are private to you. No one else can
experience your sense-data, as only you have access to your
collection of mental objects. In contrast, physical objects are
public: the same object is experienced/perceived by all perceivers.
Issues with Indirect Realism
1. Can we be sure the external world exists?
– Attacks ‘realism’ of RR: scepticism about the ‘existence’ of the external
– Response: external world is the ‘best hypothesis’- Russell.
– Responses: physical objects explain sensory coherence/ lack of choice
over our experiences - Locke
2. Can we know the external world as it really is?
– Attacks ‘representative’: scepticism about the ‘nature’ of the external
world that indirect realism lets us know.
– Response: ‘Sense data’ explain ‘relations’ between objects – Russell
– Response: The distinction between primary and secondary qualities
explains the nature of the external world – Locke.
3. There are problems arising from the view that mind-dependent objects represent mind-
independent objects and are caused by mind-independent objects. (These I am collapsing
into 2., above, and our discussion of Berkeley, to follow)
‘Realism’ sceptically attacked
Does the external world actually exist?
Accusation 1: Indirect Realism leads to
scepticism about the ‘existence’ of the
• Notion of three components
being involved in perception is too
• Given that the Indirect Realist
admits that we can know only
mind-dependent objects, what
arguments can we offer that in
fact there are mind-independent
• How can we get beneath or
beyond sense-data to prove that
objects in fact exist?
• We can only point to sense-data
in our proof of the existence of
physical objects: we cannot
logically prove that they exist in
the realist’s sense.
‘You say, though the ideas
themselves do not exist without the
mind, yet there may be things like
them, whereof they are copies or
resemblances, which things exist
without the mind in an unthinking
substance. I answer, an idea can be
like nothing but an idea; a colour or
figure can be like nothing but
another colour or figure. …I appeal
to any one whether it be sense to
assert a colour is like something
which is invisible; hard or soft, like
something which is intangible; and
so of the rest.’
- Berkeley, responding to Locke
The Sceptical Issue
This is nicely explained by Russell, in Ch. 2 of ‘The Problems of Philosophy’
The problem we have to consider is this: 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?
When we have enumerated all the sense-data which we should
naturally regard as connected with the table, have we said all there is
to say about the table, or is there still something else--something not a
sense-datum, something which persists when we go out of the room?
Common sense unhesitatingly answers that there is. What can be
bought and sold and pushed about and have a cloth laid on it, and so
on, cannot be a mere collection of sense-data. If the cloth completely
hides the table, we shall derive no sense-data from the table, and
therefore, if the table were merely sense-data, it would have ceased to
exist, and the cloth would be suspended in empty air, resting, by a
miracle, in the place where the table formerly was. This seems plainly
absurd; but whoever wishes to become a philosopher must learn not
to be frightened by absurdities.
Other Minds and Shared Objects
Here Russell weighs up an argument that since other minds exist and are in
agreement with us, there must be underlying physical objects.
‘One great reason why it is felt that we must secure a physical object in
addition to the sense-data, is that we want the same object for different
people…it is the fact that different people have similar sense-data, and that
one person in a given place at different times has similar sense-data, which
makes us suppose that over and above the sense-data there is a permanent
public object which underlies or causes the sense-data of various people at
various times...yet when we are trying to show that there must be objects
independent of our own sense-data, we cannot appeal to the testimony of
other people, since this testimony itself consists of sense-data, and does not
reveal other people's experiences unless our own sense-data are signs of
things existing independently of us. We must therefore, if possible, find, in
our own purely private experiences, characteristics which show, or tend to
show, that there are in the world things other than ourselves and our private
His response is that we cannot be sure that other minds exist…this is called
the Problem of Other Minds
• Outline and explain the argument that indirect
realism leads to scepticism about the
existence of the external world.
• The three arguments that follow perhaps are
really all arguments that rely on the notion of
• Explanatory power simply means: ‘this
hypothesis, if true, explains lots of things’.
• For each of the arguments that follow, pick
– What the things that are explained are.
– The key example that is used.
Russell’s ‘Best hypothesis’ response
From ‘The Problems of Philosophy’, chapter 2
The way in which simplicity comes in from
supposing that there really are physical
objects is easily seen. If the cat appears at
one moment in one part of the room, and
at another in another part, it is natural to
suppose that it has moved from the one
to the other, passing over a series of
intermediate positions. But if it is merely a
set of sense-data, it cannot have ever
been in any place where I did not see it;
thus we shall have to suppose that it did
not exist at all while I was not looking, but
suddenly sprang into being in a new place.
If the cat exists whether I see it or not, we
can understand from our own experience
how it gets hungry between one meal and
the next; but if it does not exist when I am
not seeing it, it seems odd that appetite
should grow during non-existence as fast as
during existence. And if the cat consists only
of sense-data, it cannot be hungry, since no
hunger but my own can be a sense-datum to
me. Thus the behaviour of the sense-data
which represent the cat to me, though it
seems quite natural when regarded as an
expression of hunger, becomes utterly
inexplicable when regarded as mere
movements and changes of patches of
colour, which are as incapable of hunger as a
triangle is of playing football…
Thus every principle of simplicity urges
us to adopt the natural view, that there
really are objects other than ourselves
and our sense-data which have an
existence not dependent upon our
perceiving them. [O]ur instinctive belief
that there are objects corresponding to
our sense-data...tends to simplify and
systematize our account of our
experiences, [and so] there seems no
good reason for rejecting it. We may
therefore admit--though with a slight
doubt derived from dreams--that the
external world does really exist, and is
not wholly dependent for its existence
upon our continuing to perceive it.
A simple cat. Needs a simple
1. Either the physical world exists or it doesn’t.
2. We cannot know for sure so we must hypothesise
3. The hypothesis which best explains agreed features of
the physical world is the one we should use.
4. The supposition that there are mind-independent
physical objects best explains agreed features of the
physical world like object permanence and
unobserved causal processes (miaow!).
5. So the hypothesis that there are mind-independent
physical objects is the one we should use.
Locke’s ‘Argument from Best Explanation’ 1
‘Essay concerning Human Understanding’ (1690) (Book 4, chapter 11)
Argument: our lack of choice over our experiences is only explained
by the existence of physical objects: a rose, the taste of sugar, the sun.
When my eyes are shut, I can choose to recall to my mind the ideas of light
or the sun that former sensations have lodged in my memory, or choose to
set such ideas aside and instead take into my imaginative view the idea of
the smell of a rose or the taste of sugar. But if at noon I turn my eyes towards
the sun, I can’t avoid the ideas that the light or sun then produces in me. So
there is a clear difference between the ideas …that force themselves on me
and that I can’t avoid having…the ones I have whether I want them or not
must be produced in my mind by some exterior cause, and the brisk acting of
some external objects whose power I can’t resist. Besides, everybody can see
the difference in himself between having a memory of how the sun looks
and actually looking at it. His perceptions of these two are so unalike [it is
clear] that they are not both memory or products purely of his mind, and
that actual seeing has an external cause.
Argument: the coherence of the various senses is only explained by
the existence of physical objects, using the example of a letter to show
…Here is an example of how the different senses confirm one another.
[Consider the letter I am writing] Once those letters have been put onto the
paper…they continue to affect my senses constantly and regularly according
to the shapes that I put down on the page. A further point: the sight of those
written letters will draw from someone who reads them aloud the very
sounds that I planned them to stand for; and that leaves little reason for
doubt that the words I write really do exist outside me. The sounds that they
cause me to hear couldn’t come from my imagination or my memory. The
letters will cause a long series of regular sounds to affect my ears—too long
for my memory to be able to retain them in the right order; and because the
sounds come to me whether I want them or not, they couldn’t be the effect
of my imagination. (Bennett, ditto)
Locke’s ‘Argument from Best Explanation’ 2
‘Essay concerning Human Understanding’ (1690) (Book 4, chapter 11)
Issues with Indirect Realism 2
1. Can we know the external world as it really is?
– Attacks ‘representative’: scepticism about the ‘nature’
of the external world that RR lets us know.
– Response: ‘Sense data’ explain ‘relations’ between
objects – Russell
– Response: The distinction between primary and
secondary qualities explains the nature of the external
world – Locke.
2. There are problems arising from the view that mind-dependent
objects represent mind-independent objects and are caused by mind-
independent objects. (These I am collapsing into 2., above.)
Possible reply to Locke’s suggestions
• Locke has only given us some more things that we have to explain about
our senses, not an explanation about why physical objects exist.
• He seems to be arguing that we must infer the existence of physical
objects from the consistent and coherent existence of sense-data – that is
to say, (negatively) then, that physical objects are really only an
explanatory hypothesis at best.
• So he doesn’t account for our strong intuitive sense that physical objects
• And now, to Russell’s list of things to be explained, we now must also add
– How it is that our sense-data aren’t consciously controlled.
– Why it is that our sense-data cohere.
• Locke, of course, might well reply that an explanation has been asked for
by the sceptic and he has given one – it is, therefore, the sceptic who
seeks rational explanations of our intuitions and is, thus, committing a
category error. (Locke’s mistake, then, if there is one, is only in taking the
Can we know the external world
as it really is? Some sceptical thoughts.
• Assume, hypothetically, that the external
world does exist: accept the argument
from best explanation.
– But what is the world’s nature?
• Key Question: If we know it only through
representations, could there be a gap
between how we see the world and how
it really is?
– Re + Presentation – even the shape of
this word shows there is a gap…
– How representative is our view of the
way the world really is?
• [Worse: solipsism…If sense-data are
private to the individual: could there be a
gap between how the individual sees the
world, and how others see it?
• Might the world of representations have
only one inhabitant?]
How can you check the correctness of
your mental image if you don’t have
direct access to the real?
How can you check the reality of the
cinematic image, if you cannot leave