Knowledge of the External World
An Introduction to Three Theories
© M.Carmody and P. Sheehy
1
Knowledge of the External World – Theories of Perception
We ordinarily take ourselves to possess knowledge of the world through our
senses. We see, hear, smell, touch and taste things. By doing so we come to
know about things in the world around us. Our perception of the world tells us
about the world.
When I look at the small white horse eating some hay I know how things
appear to me. I can describe the horse, its shape, colour, the yellowness of
the hay. If close enough I can tell you how the beast smells.
A philosophical worry now arises. While I am an impeccable reporter on how
the horse and hay appear to me, should we think that the way something
appears in one’s perceptual experience tells one how things really are? That
is, how should we consider the relationship between appearance and
reality?1
Misperceptions or illusions (e.g. seeing something in a way other than it really
is) and hallucinations (e.g. seeing something that is not really present at all)
present problems. If our senses can mislead us, how are we to know that
things are as they appear, unless we already know that our senses are
presenting things as they are?
Even more fundamentally in the study of perception how are we to explain
how we can both perceive and misperceive how things are in the world
around us? The task of the philosopher is to offer an account of what it is that
we are aware of or experiencing in perception and of the nature of the
relationship between the person (subject of experience) and the objects
perceived.
To these problems we can add the question of what happens to an object
when it is not perceived and what can be said (truly) of it. When I leave the
room what can I know about the unperceived contents of the room? You will
no doubt be familiar with the question of whether the (unperceived) falling tree
in the forest emits a sound as it hits the ground. In the way one addresses
these issues one is committing to a theory of perception.
We shall examine three influential philosophical responses to these questions
in the shape of three families or theories of perception.
(1)
direct realism (the ‘common-sense’ theory)
(2)
indirect or representative realism
(3)
idealism
To begin these families can be very roughly characterised:
1
An issue to be discussed further when we look at scepticism.
2

The common-sense or direct realist theory maintains that the world is as
it is perceived. There is a world with objects that exist independently of
human perceptions. In perception (seeing and so on) I have a direct
awareness of the object. Direct realism not only denies that our
experiences are merely subjective, but also denies that perceptions are
reduced to mere sense-data.

The representative theory of perception maintains that sense-data in our
minds represents objects in the world around us. Those objects exist
independently of us and are the cause of the sense-date we experience.
However, we never have direct awareness of the objects in the world.

Idealism is a form of anti-realism. Its central thesis is that all our
experiences are experiences of mental representations. There is no world
of material objects (as we ordinarily think of them – that is, as physical
objects ‘out there’ in the world and which cause our beliefs, ideas and so
on) to be known. There are only minds and their ideas (and God). Material
objects are to be understood as families of experiences. Historically, it can
be seen as a response to the problems of representative realism, and in
particular the danger that it leads to scepticism. In the words of its key
defender, Berkeley, ‘to be is to be perceived’.
Let’s look in more detail at the motivations and problems faced by these
approaches. 2
2
For the sake of completeness we should mention a fourth theory, Phenomenalism. Like
Idealism this is also a form of anti-realism. One does not perceive a mind independent world,
but the only thing(s) which we can be (directly) aware of (the only possible objects of
awareness) are complexes/combinations of actual experiences (complexes of sense-data or
sensations). Phenomenalism is characteristically understood as a semantic thesis (Ayer).
Statements asserting the existence of physical objects are equivalent in meaning to
statements describing sensations. The phenomenalist claims that to say that a physical object
exists is to say that someone would have certain sequences of sensations were they to have
certain others. To be is not to be perceived, but to be perceivable. Phenomenalism is not
discussed any further here because it is not a feature of the AQA AS syllabus. For some more
on the theory visit the Knowledge of the External World section at www.richmondphilosophy.net or Blackboard.
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Direct Realism
If you find yourself chatting about theories of perception or confronted by an
examination question on the topic, then you might think about structuring a
discussion around key issues.





What do we mean by direct realism?
What motivates it?
What problems does the position face?
How can one respond to those problems?
What commitments does the response(s) entail?
Direct realism: what and why
Why the ‘common-sense’ theory? When we look at an object what we see is
the object, which is directly open to our experience. Our perceptual
experience is direct in that it is unmediated by awareness of or interaction with
any kind of subjective entities (sense data). The things in the world cause our
perceptual experience. The things in the world exist independently of us, and
so continue to exist when being unperceived. Following Jonathan Dancy we
can distinguish between naïve and scientific direct realism. The naïve version
allows that objects retain all their properties when unperceived; the scientific
version that objects retain just their primary or categorical properties (i.e.
basic properties like shape rather than properties like colour or taste. More on
the distinction between primary and secondary properties below). Note – in
the literature ‘direct realism’ is sometimes used interchangeably with ‘naïve
realism’. Don’t worry; just ensure you make clear the terms and distinctions
you are employing.
One can say that a motivation to endorse direct realism is that it accords with
common-sense. Rather more needs to be said to explain the force and merit
of such a claim. After all, one may wonder why common-sense should be
taken to recommend a philosophical position or, indeed, one may just wonder
what counts as common-sense in any case.3 Some points to consider are:
3

Direct realism reflects the sense that the world is (causally) responsible
for our perceptual experiences. At the level of experience we do not
seem to shape the world through our beliefs and desires

The independence of material objects is consistent with the stability of
our perceptual experience. Objects typically do not suddenly change as
I look at them and, crucially, typically do not change when I am not
looking at them. Their independence as material objects explains their
continued unperceived existence. This helps to give a very
straightforward account of the truth conditions for statements such as
‘the television currently in my flat is white and in the front room’ when I
utter that outside of my flat.
The nature and role of common-sense is a matter of longstanding discussion in philosophy.
4

The view that material objects are independent of us explains why error
and disputes occur. It also points to an account of how such mistakes
can be corrected and disputes resolved. We need to attend to how the
world is with greater care and accuracy.
Challenges
The reasons to be a direct realist may just be reasons to be a realist.
However, the directness of direct realism gives rise to worries concerning the
connection or relationship between the perceiver and the world.
The gap between perceiver and the world invites the sceptical challenge. How
can I know that the object I am looking at really is like that? Hmm, well isn’t
that a problem for realism? We’ll return to the challenge of scepticism in the
final part of the course.
A second kind of challenge relies on the view that there is a time lag between
my perception of an object and the object actually having the properties I
perceive it to possess. This is the Time-Lag Argument.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
there is a time lag between my
perception of an object and the object
actually having the properties I
perceive it to possess.On a clear night,
I see the three stars of Orion's belt:
Alnitak, Alnilam and Mintaka.
Alnitak is 800 light years away, Alnilam
1300 light years away and Mintaka is
900 light years away.
This means the light has taken 800,
1300 and 900 years respectively to
reach me.
So, in principle, they could have
ceased to exist some 500 years ago.
But I see something now.
So, how can I be seeing the stars directly if they could not actually
exist?
There must be a difference between the immediate (direct) objection of
my perception, the sense-datum or idea, and the mediate (indirect)
object of perception, the stars themselves.
So, direct realism must be false.
This is a well-known objection to direct realism but one that is easily
answered. It trades on a confusion between two senses of immediate.
Immediate #1: without delay
Immediate #2: direct, without anything coming between.
5
Now, it is of course true that the light from the stars does not reach me
immediately. The light from everything takes some time to reach me. I see the
sun as it was about eight minutes ago. Thirty metres up at my desk, the
horizon is about 20km away and I see it as it was about 70 microseconds ago.
In a sense, you never see the world as it is right at that moment.
But this doesn't mean that anything gets between you and what you see. It
just takes time to see what you see.
Here's a comparison. Looking at this picture, I see a young
woman's face. I am told that there is also an old woman's face. I
can't see it for a few seconds – and then I see it. It took time to
process the data and ‘find’ the image but nothing got between me
and the image. It was immediate in one sense, but not in another.
Here's another comparison. I look outside the window and form the
belief that it is raining. My belief represents the world just like a
perception does. There is nothing ‘between’ my belief and the world
– and equally nothing between my perception of the world and the
world. Now, that belief was immediate in the sense of taking no
time. Suppose now I pass a house on the street with the door open. I hear
footsteps inside and furniture being moved. I notice the ‘For Sale’ sign lying
on the ground and that there is an unsorted pile of stuff in the front room. After
a couple of seconds' thinking, I form the belief that someone is moving in. My
belief was not immediate in the sense of taking time but immediate in the
sense of there being nothing between me and the world. My forming the belief
here is like my perceiving the star. There is a ‘time-gap’ between what's
happening in the world and my representing it. But there is no intermediary
entity in either case.
Misperception and Illusion
While the time lag argument trades on a misunderstanding there remain
problems for direct realism in explaining misperceptions. For example, a
round coin can appear elliptical from certain angles, a straight stick bent when
in water, parallel lines convergent as they move into the distance, a nonexistent limb can feel painful to an amputee4 (the argument from illusion). The
basic problem is how to explain why an apparently direct relationship with the
world can give rise to such errors.
In the last case we’ll set aside difficulties about something that’s not there hurting. The point
is that it seems to the amputee that there is a limb with a pain; yet she knows there is not.
4
6
A related problem emerges when we consider the possibility of hallucinations.
I may have an experience as of seeing a small green man standing before me
when there is no such man. In such a case the perceptual experience is nonveridical. It may seem easy enough to explain the cause of the experience for example, the drug I had just ingested. However, the feel or
phenomenology of the experience is indistinguishable from a veridical one
(i.e. when there is a small green man standing before me). The challenge is
to explain what it is that forms the object of one’s perceptual experience such
that the qualitative experience is the same. One suggestion is that perceptual
experience is experience of the way the world seems. The way the world
seems is revealed to us in our experience of sense-data via which we do
experience a world of independent objects (indirect realism).
For the moment we can add a further problem. Physics tells us how the world
really is. Yet we do not experience the world as it is described in our best
physical theory, even though according to direct realism it is with the world as
such that I have direct contact.
In the final section we shall consider how direct realism might address its
problems. Next, we shall examine one historically influential response to the
problems faced by the realist - Representative Realism.
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Indirect or Representative Realism
Faced by the challenges to direct realism, particularly the view that the realist
struggles to explain the obvious fact that we do suffer misperceptions and
illusions, the realist can suggest that our direct awareness is of inner, mental
objects representing the thing out there in the world. That is, we preserve
realism by introducing sense data.
This is an indirect form of realism. It is realist in holding that world of mindindependent object exists; that there is a real world out there. It is indirect in
explaining that our perception of objects is through one’s being directly aware
of an inner, mental representation of the object. That inner mental
representation is caused by the object out there in the world. So, my seeing
the computer on my desk is not a direct visual experience of the thing on my
desk, but my being directly aware of the representation in my mind of that
object. This kind of analysis of perception was endorsed by Descartes, Locke
(see next section) and Hume.5
The inner mental objects of which one is directly aware in perceptual
experience are combinations of (our old friends) sense-data. Our knowledge
of objective (mind-independent) reality consists in knowledge of facts about
one’s own subjective experience. Let’s spell out in a bit more detail what
philosophers have meant by the concept of a sense-datum (sense-data is the
plural) and why it has figured importantly in indirect realism and anti-realist
approaches. After considering this issue we shall investigate in more detail
the motivations for representative realism.
Sense-Data
What are they?
If I see a dagger or hallucinate one, it looks the same. There is a daggershaped object in my visual field. This object is called a (visual) sense-datum.
A visual sense-datum is a two-dimensional object with a certain shape and
coloured a certain way.
My current visual experience is mosaic of such objects – of sense-data. As I
look at the white disc before me, there is a white circular sense-datum as part
of my visual experience. As I tilt the disc, it is replaced by a white elliptical
sense-datum.
Notice therefore that there is a distinction between the three-dimensional
object in the world that remains the same and the two-dimensional sense-data
that exist only so long as my visual experience does not change.
5
For the first half of the twentieth century indirect realism and phenomenalism were perhaps
the dominant philosophical theories of perception. There has subsequently been a shift in
favour of direct realism. For why one should be a direct realist see the final section. Note that
a shift in favour is not in itself an argument for the truth a theory.
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Why believe in them?






The Primary/Secondary Quality Distinction. Objects don’t really have
colours or tastes, according to science. They are features of my ideas or
sense-data. More on this soon.
Perceptual relativity. There is a distinction between an object and its
appearance: the circular disc may appear elliptical. We need to account for
the fact that there is a circular thing in my visual experience.
They explain misperception: the stick is not really bent but the sticksense-datum is.
They explain hallucination: in normal perception, a real dagger causes a
dagger-sense-datum in my visual experience.
They explain how we can ‘see’ stars that may now be dead: the star’s
light emitted millions of years ago causes a star-sense-datum when it
reaches me.
They fit in with modern physics: nothing is really coloured – colours are
the properties of sense-data caused by the interaction of objects, light, my
eyes and my brain.
So, granting for the moment that there is reason to accept sense-data why
endorse Representative Realism? As noted above the motivations for
representative realism can be seen as ways of responding to the problems of
the direct form of realism.
Hallucinations, Dreams and Illusions.
When I see a small white horse I have a
certain perceptual experience. I may have
just the same perceptual experience if I
have a dream or hallucination of a small
white horse. From my subjective point of
view the perceptual experiences are
indistinguishable. The only difference
between really seeing a small white horse
(veridical perception) and hallucinating one is the cause of the sensation. In
veridical perception, the effect (the internal image of which one is directly
aware) represents the cause - the small white horse - in some more or less
accurate way. In the case of hallucination the cause - drugs in the
bloodstream, maybe - is misrepresented.
The Fallibility of One’s Knowledge of the External World
We know that we can be mistaken about how things are in the world. Our
perceptual experience may not always deliver true beliefs about the state of
the world. That there is a gap between perception – how things appear – and
the world – the way things are – has been identified as a something direct
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realism struggles to explain. This is not a problem for indirect realism. One’s
perceptual experiences are typically a reliable guide to how things are in the
world. However, things can go wrong in many ways – a breakdown in the
causal links between the world and me, unusual circumstances, the
stimulation of the mind by, say, drugs. For the representative realist the
formation of false beliefs about the world can be explained by appeal to our
direct awareness of sense data that have been produced in some deviant or
unusual way. The explanation of our knowledge of ‘external’ or physical reality
as based on our more certain knowledge of one’s subjective experience – our
knowledge of how things appear – is thus consistent with the explanation of
how we can come to form false beliefs about reality.
Hmm. One might still worry that there is a gap between our experience and
the world. Why think that my perceptual experience is a good guide to how
the world is. This gap prompts the sceptical worry that knowledge about the
external world may not be attainable. More on this concern when we look at
Berkeley.
The Appeal To Introspection
Here the argument holds that each person knows from his own case that
when he is aware of an object his perceptual experience or state has its own
nature. There’s something that it’s like for you to see the table or hold the
cup. Two people aware of the same object will be in different perceptual
states, a difference that can be described as a difference in content. The
different states have different perceptual content. Peter and Paul may be
looking at the same painting, but each is in a distinct perceptual state. Each
has its own content, and what can the content of a person’s awareness (e.g.
Paul’s of that painting) be other than an object of awareness? A person is
aware of the content and it is in virtue of this that each person is able to be
aware indirectly of the material objects of the world.
Just as direct realism divides into naïve and scientific so too does indirect
realism. The naïve form maintains that the inner object of awareness has
properties of all the kinds that the physical object has. Scientific indirect
realism (much the commoner view and the one associated with e.g. Locke)
holds that the (indirect) object out in the world has only the primary qualities,
and that the sensory (secondary) properties feature only in one’s experience
of that object As Locke put it: there is nothing like the sensory properties in
the indirect object. Primary qualities are supposed on this view supposed to
be the ones that are shared by the mental representation and the physical
object it represents.
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Primary and Secondary Properties
Along with his contemporary philosophical and scientific peers Locke notes a
distinction between the kinds of properties any object possesses. The
distinction is between primary and secondary properties.

A primary property is basically a property that is completely inseparable
from an object. These are properties of shape and size, solidity, motion
or rest, location, number.

Secondary properties are those such as colours, tastes, smells, feel
and sounds.
That an object has its primary properties (and that we perceive them if our
senses are working) does not depend on the observer. The shape and
location of the small horse that I observe are entirely dependent on the horse.
By contrast the secondary properties of an object, such as the colour and
smell of the small horse, are dependent on the perceiver. To put matters
crudely the primary properties of shape and so on are entirely in the world
while the secondary properties are in part a feature of the observer.
Why make this distinction?
1.
Consider your experience of a red flower. You see it as red. That is,
your perceptual experience has a certain qualitative feel. It is like
something to perceive redness. In non-defective or impaired cases that
something for creatures like us is to be explained in terms of the ways
in which our sensory apparatus is stimulated the environment. Light
waves reflect off the surface of the flower at a wavelength that
stimulates a red sensation in creatures like us. In a dog or Martian the
sensation need not be as it is for us. Of course the way in which the
flower is perceived is in part down to the structure of its surface and its
reflective properties,6 but the perceiver makes a vital contribution to the
way in which it is experienced.
2.
The dependence of secondary properties on the nature of the observer
is further supported by the way in which sensible properties (colours,
tastes and the like) of an object can vary according to the context or
perspective of the observer. A white cube in different lighting conditions
will appear various colours while remaining the same shape. Also, the
6
A different enough structure and we experience the surface as possessing a different colour.
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sensible properties one perceives depends on the sense modalities
that one possesses. A blind person can perceive no colours. However,
he can perceive its primary qualities of shape, size, position and so on
through touch. A more general moral can be drawn from this kind of
example. Our perception of primary properties is not restricted to any
one particular sense. A blind person can not see shapes and sizes but
can nonetheless perceive these properties through touch. The
perception of secondary properties, though, does require the perceiver
to possess the particular sense. I need to be able to see and smell to
experience the colour and scent of the rose as coloured and
possessed of odour.
3.
The most important motivation for the distinction was the scientific
understanding of the nature of the physical world that emerged from
the advances of the scientific revolution of the 17th century. The natural
world was constituted by ‘bits’ of basic matter or physical substance.
These atoms possessed the basic properties of size and motion. In
themselves such corpuscles (the commitment to this atomistic physics
was known as ‘corpuscularianism’) did not have any colours, smell,
taste and so on. Instead, they possessed the power to cause ideas of
secondary properties in suitably equipped perceivers. Or more
accurately, when atoms are arranged in certain configurations they
have the power or disposition to produce certain kinds of sensation in
certain kinds of perceivers. Thus, when atoms are organised in a
pattern constitutive of a red rose they produce in a creature like me the
sensation of redness.
When we perceive an object, according to Locke, our ideas of its primary
properties resemble the properties in the object itself. The object does actually
– on its own, so to speak – have those qualities. Our ideas of secondary
properties do not resemble any quality an object has, but are rather the
product of the ways in which we interact with the object.
Before moving on let’s take a closer look at some of Locke’s arguments in his
Essay On Human Understanding for the primary/secondary quality distinction.
1. ‘Divide a grain of wheat into ever smaller parts. Each part will still have
extension, shape and solidity but we will destroy the taste, feel and smell
of the wheat.’ (II, viii, §9)
2. ‘We are inconsistent in how we think about sensory qualities. If I draw near
a fire, I experience warmth, which I think is a quality of the fire. But if I
draw closer, I experience pain, which I don’t think is something ‘in’ the fire.
We should think that neither warmth or pain are in the fire but ideas in me
produced by the fire.’ (II, viii, §16)
3. ‘Take some porphyry (a purply-white rock). Turn the lights off. You can no
longer see the colours. Have we changed the porphyry? No. So, the
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change is in us: we no longer have the ideas of purple and white.’ (II, viii,
§19)
4. ‘Pound an almond and you change the colour from white to grey and the
taste from sweet to oily. Yet all we have done is re-organised the matter in
the almond.’ (II, viii, §20)
5. ‘Put one hand on the radiator and the other on ice then plunge both hands
into the same bucket of warm water. One hand will feel warm and the
other cold. Is the water both hot and cold? No. Warmth and coldness are
in us, not in the water.’ (II, viii, §21)
6. ‘If we had better senses – or if we used a powerful microscope – we would
see that things change their appearance. For example, under a
microscope, blood is no longer red but red discs floating in a transparent
liquid.’ (II, xxiii, §11)

In sum:
o By altering any object, you can destroy secondary qualities
but you cannot destroy primary qualities.
o Primary qualities are not dependent on having a certain
sense-organ but are common to all senses.

The distinction has been questioned by philosophers ever since.

Berkeley argued that we can only conceive of things in terms of secondary
qualities and hence that there were no good reasons for thinking that there
were primary qualities as well.
Locke’s notion of resemblance is extremely unclear. If I look at a tennis ball, I
have a circular idea of a spherical object. A two-dimensional circle does not
resemble a three-dimensional sphere. Only another three-dimensional sphere
can resemble a sphere.
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Idealism
George Berkeley (1685-1753)
Idealism is thesis that all our experiences are
experiences of mental representations. There is no
world of material objects as we ordinarily think of them
– that is, as physical objects ‘out there’ in the world and
which cause our beliefs, perceptions, feels and so on.
Material objects are to be understood as families of
experiences. There exist no objects independent of the
mind. Moreover, nor could we know them if they did.
What exists are minds and their ideas (in the broad
sense common among philosophers in the seventeenth and eighteenth
centuries which includes beliefs, thoughts, sensations, feelings and so on). In
Berkeley’s phrase ‘to be is to be perceived’. Idealism is an anti-realist theory
of perception. Our perceptual experience and knowledge is not analysed as
being caused by a mind independent reality which is at least in part (causally)
responsible for our perceptual states.
On its face Idealism is a crazy view. Its most influential advocate, George
Berkeley was widely criticised by his contemporaries and subsequent
philosophers. However, neither Berkeley nor his thesis are crazy and certain
criticisms can be dismissed as simply resting on misunderstanding the
arguments he had advanced. This is not to say that we should agree with
Berkeley, but we do need to understand the motivations for his claim and the
argument offered in support of them. Only then will we be in a position to
evaluate the merits of Idealism.
Why Idealism? Let’s see where Berkeley begins.
1. He is responding to Descartes and Locke. Berkeley has the broad aim of
attacking scepticism and defending common sense; he also sought to
attack atheism and so to defend religion.
2. Berkeley agrees with Descartes and Locke that we experience directly the
contents of our mind – it is ideas (sense data) of which we are immediately
or directly aware in experience.
3. The danger of scepticism arises once we acknowledge that there is a gap
between the contents of our experience and the claim that our experience
is of a world beyond or independent of our senses. There is a gap between
me as a subject of experience and the real world. That is just the gap which
exists on the Lockean account of perception. The objects in the world
cause in us a perceptual experience. On the basis of that experience we
judge the object to exist and to possess certain properties.
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4. According to Locke objects really possess their primary properties like
shape and location while they possess the power to cause in observers like
us the experience of secondary properties like colour or sound.
Now, Berkeley is committed to an empiricist account of knowledge. If we are
to have knowledge of the world (of the things in it) we need to close the gap
between reality and experience (or appearance). This leads Berkeley to the
view that:

It is only if physical objects are conceived as collections of ideas
which hang together in experience that we have any empirical
evidence for their existence.
Further, the distinction drawn between primary and secondary properties
cannot support the view that there are mind independent objects. Remember
Locke maintained that the primary properties of an object belong to it
independently of any act of perception while its secondary properties only
exist in the act of perception. On this picture of the world and our relation to it
objects possess properties or qualities in virtue of which we have perceptual
experiences. The primary properties represent how the object really is – the
properties it possesses independently of anyone perceiving it.
However, the reasons for thinking that secondary properties are minddependent also apply to our perception of primary properties. The colour or
smell of an object can vary depending on the observer. So too can primary
qualities like shape. Moreover, it seems impossible to conceive of primary
properties existing apart from secondary properties. Try to think of an object
without shape or colour. The qualities of an object taken all together seem to
be equally mind-dependent. So, Berkeley holds that:

If knowledge is grounded in experience (empiricism), then we
have no perceptual experience which grounds the claim that there
exist mind-independent objects. We have no epistemological
access to the underlying matter or substance (in the world) which
would be the bearer of the properties we experience. Such a
substance is empirically undetectable and so cannot figure in a
proper understanding of the world.
The mistake we make which leads to the view that trees and houses exist
independently arises from our habit of making abstractions. This is defined by
Berkeley as the practice of treating as (really) separate things concepts which
can only be separated in thought. We have already seen one example above
in the case of taking something’s shape to be separable in reality from its
colour.7 In our perceptual experience we abstract from our experience of
certain combinations of ideas the mind-independent existence of those
7
Of course a thing could have a different shape and/or colour. Here, though, the point is that
it cannot just have shape and no colour. Nor can a patch of colour just be coloured. It must
have a shape. If in doubt try to imagine a blotch of red without the blotch possessing a shape.
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objects. But this is a contradiction. Let me explain with reference to Berkeley’s
line of argument in his Principles of Human Knowledge (1710).
From our experience we are compelled to recognise that:
(a)
We immediately or directly perceive ideas. The content of our
experience is grounded in our perception of qualities or properties.
Collections of sensory perceptions occur with regularity and stability so
that they come to be named, ‘and so reputed to be one thing’, such as
an apple or tree (Principles 1).
(b)
There is something distinct from what is perceived. This is the mind or
soul or myself. (Principles 2)
(c)
One’s ideas (e.g. beliefs) cannot exist except in the mind perceiving
them. (Principles 3)
(d)
It now follows that if objects are collections of qualities and qualities are
sensible ideas, then objects are sensible ideas. Their essence is to be
perceived: esse est percipi. Nor is it possible that they should have any
existence out of the minds or thinking things that perceive them.
(Principles 3)
(e)
This claim may appear shocking, but there is no scope to allow that
objects have a perception-independent experience. ‘For what are the
aforementioned objects but the things we perceive by sense, and what
do we perceive besides our own ideas or sensations; and is it not plainly
repugnant [i.e. illogical] that any of these or combination of them should
exist unperceived?’ (Principles 4)
(f)
Now since things are bundles of ideas and ideas only exist if
perceived by minds, the notion of ‘absolute existence without [i.e.
without reference to or independent of] the mind’ is a contradiction.
(Principles 5)
Berkeley recognises that Idealism maintains that an object only exists if
perceived. Of objects it is true that ‘so long as they are not perceived by me,
or do not exist in my mind or that of any created spirit, they must have either
no existence at all, or else subsist in the mind of some eternal spirit’
(Principles 6). That spirit is God. My desk persists when there is no-one in the
room because it remains an idea in the infinite mind of God.
Berkeley develops an account of knowledge which closes the gap between
how things appear in perception and reality. In his Three Dialogues (1713)
Berkeley spells out why we should endorse Idealism. In his Master Argument
Berkeley explains that the very act of conceiving of something means that its
existence is necessarily mind-dependent.8 While we do of course make
8
See Appendix, The Master Argument in the Three Dialogues
16
perceptual errors, the threat of a generalised sceptical worry is refuted
according to Berkeley because there is no gap between our experience of the
world and reality. We are not minded subjects in a world of a physical world of
substance. Rather, the nature of reality is mental. What we typically label as
physical objects are bundles of ideas. To be a perceiver is to be a mind. The
constituents of reality are minds and their ideas. Beginning from a concern
about what we can claim to know Berkeley arrives at a monistic picture of the
nature of the universe – its ultimate nature is mind.
Some Challenges to Idealism

It is absurd. Samuel Johnson, author of the first English dictionary, was
arguing with his friend and biographer, James Boswell about Berkeley’s
idealism (then known as ‘immaterialism’). Johnson said it was obviously
false that there was no matter and just ideas but there was no way to
disprove the thesis. Johnson kicked a nearby stone and said, ‘I refute it
thus!’ Of course, while it is absurd to doubt that there is a stone there upon
kicking it, there is nothing in the experience that can show Idealism to be
false. Simply pointing to the evident absurdity of the position is, then, no
real argument against it. Perhaps, it just shows the need to reconsider
what we consider absurd.

It is expensive. Instead of the world being the source of our experiences,
we have to suppose God is. How can I be sure God exists? Is it enough to
say that something must keep things in existence when we are not looking
at them? If it is, why does this have to be God? Could it be the joint work
of the minds of a number of lesser Gods? Note that the objection is not
motivated by atheism. Rather, the appeal to God to explain our perceptual
knowledge looks desperate as a feature of an epistemological theory.

It is confused. Berkeley’s Master Argument is that everything is minddependent because the very attempt to conceive of something mindindependent is impossible: in conceiving of it, you involve your mind. This
is a confusion of two thoughts:
o You cannot conceive of anything without conceiving of it.
o You cannot conceive of anything unconceived.

The first is trivially true. To think of anything I have to think and hence
there’s a mind involved.

The second is not true. I can think of a world in which there are no minds.
Just because I am thinking of it, I am not involved in it.
o Compare: I can’t paint a painting without painting. But I can paint
a painting that doesn’t contain me, the painter, in it.
17

It leads to solipsism. How can I be sure that there are other minds if all I
experience are ideas?
Direct Realism Revsited
So, where does this leave us? The apparently obvious problems of the
common-sense theory motivated the appeal to sense-data and the emphasis
on the inner domain of appearances. However, the move away from direct
realism has produced theories which face serious problems of their own. One
problem which we have left lurking in the shadows is worth spelling out in a
little more detail. This is the claim that we have little reason to accept the
existence of sense-data. Absent sense-data and indirect and anti-realist
approaches face a major problem. In pointing to the difficulties faced by
alternative theories the defender of direct realism may be said to be poisoning
the wells of his rivals. Having investigated the poison we shall see what can
be said more positively in defence of direct realism.
Why reject sense-data?

The object/appearance argument is mistaken. To take an example from
Austin:
o “If … a church were cunningly camouflaged so that it looked like
a barn, [then we] see, of course, a church that now looks like a
barn. We do not see an immaterial barn, an immaterial church,
or an immaterial anything else. And what in this case could
seriously tempt us to say that we do?”9
o In general, if X looks to have the property P, then it is a mistake
to think that there must be something else that is P.
o Just because “appearance” is a noun, it does not mean it refers
to a thing: “lap” is a noun but laps aren’t things.

Where are they? Sense-data are not part of the external world. They are
mental entities. Most philosophers and scientists believe that the mind is
the brain. If so, then sense-data are in my brain. But you will not find any
coloured two-dimensional objects in my brain.
o If you believe that the mind is something distinct from the brain –
a non-physical thing – then you do not have this problem.
o It is often argued that sense-data aren’t really in my brain as
shaped, coloured objects. They are identical with brain-states.
When neurons in my visual cortex behave in such-and-such a
way, I have a red square sensation.
o If so, then you no longer believe in sense-data because there
are no longer objects that bear the properties we experience –
no square object that has the property of being red.
9
Austin (1962), Sense and Sensibilia, p. 30
18

Scepticism. If I can only directly perceive my sense-data, how can I be
sure that they properly portray the world beyond? It seems I cannot. I am
trapped behind a “veil of perception”. This is surely not a consequence we
want to draw from a theory of perception.

The Speckled Hen. I see a speckled hen for a moment and I am unsure
how many speckles it had. I experienced a speckled-hen sense-datum.
The sense-datum is meant to have just the appearance properties I
experience.
o It follows that the sense-datum had an indeterminate number of
speckles. But a sense-datum can’t be indeterminate. It is a
complete appearance.
o So, we’d have to say that I simply didn’t see the sense-datum
clearly enough to determine how many speckles it had. But this
can’t be right: there is no “gap” between the sense-datum and
my experiencing it.

Private objects. Sense-data are private entities. My sense-data exist in
my mind alone. Only I can talk about how things seem to me. According to
Wittgenstein, the idea of a private language is incoherent. If so, so are the
private sense-data the language is about.
Perhaps we should see if the direct theory can be articulated in a way that
allows us to dissolve the illusion problems and allow an account of how error
is possible.
There may be no knock-down argument for direct realism but the plausibility
of the view can be supported by the way it deals with the criticisms it faces.
Some points to consider:

It is part of a common-sense realism to allow that there can be
variation in the way things look. Objects are perceived in different
contexts and that may explain why the very same object can be
experienced differently. Furthermore, we do not say that the world just
looks or seems a certain way. Rather, we maintain that it is a certain
way and it is only if we adopt this approach that we can account for
error and settle disputes. This kind of approach may not convince,
though. The appeal to common-sense may just appear to beg the
question.

John McDowell (1942-) argues that
there is a difference between the
experience of a person having a
veridical perceptual experience and
one who is having a non-veridical
experience purportedly of the same
object. There may be no difference
19
from the inside, but the key distinction is the absence of the object in
one of the cases. In the case of really perceiving a tree, the tree is
present in the experience of the perceiver. We have no reason to think
that she is experiencing sense-data rather than the tree itself.
McDowell appeals to external factors (of which the person having the
non-veridical experience is not going to be aware) in order to show that
there is no (relevant) common factor between the cases.

Perceptual states are belief states or a mixture of belief states and
sensations. The problem of misperception or hallucination becomes a
species of the problem of false beliefs. There is sometimes a mismatch
between our beliefs and the world in virtue of which a belief turns out to
be false. This is a general problem in epistemology, so the direct realist
need not feel any particular embarrassment when confronted by the
problem of misperception.

Your perceptual states are caused by the objects in the world. The
mechanisms through which this causal relation is to be unpacked are
the subject of e.g. physics and neuroscience. If there is a causal
connection between our internal (brain) states and the world, then
misperception and non-veridical experience can be explained in terms
of how one is connected to the world and how particular states in the
world affect the individual. This is a direct connection which permits
error and misperception. Moreover, our physical and neurological
structure is such that in experiencing the world directly that experience
has a certain character and feel. If I see a brown chair on fire (and
there really is a chair on fire ), then to experience it directly is, inter alia,
to have certain colour, shape and olfactory sensations through the
proper functioning of my cognitive and perceptual mechanisms. Hence,
there is no need to appeal to any inner sense-data.

A rather different form of response is that our conceptual framework
presupposes a world of objects of which we have direct knowledge.
The work to be done here is to show that both realism and direct
perceptual knowledge must go together.
The attempt to defend realism leaves one committed to addressing or
diffusing sceptical worries. One will also have to ensure that an endorsement
of realism is consistent with one’s views on the source and nature of
knowledge.
20
The Master Argument in the Three Dialogues
PHILONOUS: But (to pass by all that has been hitherto said, and reckon it
for nothing, if you will have it so) I am content to put the whole upon this
issue. If you can conceive it possible for any mixture or combination of
qualities, or any sensible object whatever, to exist without the mind, then I will
grant it actually to be so.
HYLAS: If it comes to that, the point will soon be decided. What more easy
than to conceive a tree or house existing by itself, independent of, and
unperceived by any mind whatsoever? I do at this present time conceive
them existing after that manner.
PHILONOUS: How say you, Hylas, can you see a thing which is at the
same time unseen?
HYLAS:
No, that were a contradiction.
PHILONOUS: Is it not as great a contradiction to talk of conceiving a thing
which is unconceived?
HYLAS
It is.
PHILONOUS:
by you?
HYLAS
How should it be otherwise?
PHILONOUS:
HYLAS:
The tree or house therefore which you think of, is conceived
And what is conceived, is surely in the mind?
Without question, that which is conceived is in the mind.
PHILONOUS: How then came you to say, you conceived a house or tree
existing independent and out of all minds whatsoever?
HYLAS: That was I agree an oversight; but stay, let me consider what led
me into it. - It is a pleasant mistake enough. As I was thinking of a tree in a
solitary place, where no one was present to see it, I thought that was to
conceive a tree as existing unperceived or unthought of, not considering that I
myself conceived it all the while. But now I plainly see, that all I can do is to
frame ideas in my own mind. I may indeed conceive in my own thoughts the
idea of a tree, or a house, or a mountain, but that is all. And this is far from
proving, that I can conceive them existing out of the minds of all spirits.
PHILONOUS: You acknowledge then that you cannot possibly conceive,
how any one corporeal sensible thing should exist otherwise than in a mind.
HYLAS:
I do.
21
Examination Questions
2007
(a) Briefly explain what philosophers mean by sense-data. (6 marks)
(b) Explain and illustrate one criticism of representative realism. (15
marks)
(c) Assess phenomenalism. (24 marks)
2006
(a) Briefly explain what philosophers mean by the primary qualities of an
object. (6 marks)
(b) Outline and illustrate how illusion creates a problem concerning
perceptual knowledge. (15 marks)
(c) Assess representative realism. (24 marks)
2005
(a) Briefly explain one difference between idealism and
phenomenalism. (6 marks)
(b) Explain and illustrate why dreaming may lead to scepticism about
our perceptual knowledge. (15 marks)
(c) Assess naïve realism. (24 marks)
2004
(a) Identify one similarity and one difference between idealism and
naïve realism. (6 marks)
(b) Explain and illustrate one criticism of phenomenalism. (15 marks)
(c) Assess idealism. (24 marks)
2003
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(a) Identify two differences between naïve realism and representative
realism. (6 marks)
(b) Explain and illustrate one criticism of naïve realism. (15 marks)
(c) Assess representative realism. (24 marks)
2002
(a) Identify two ways in which sense data differ from physical objects. (6
marks)
(b) Explain and illustrate the distinction, made for example in
representative realism, between the primary and secondary qualities of
objects. (15 marks)
(c) Assess phenomenalism. (24 marks)
2001
(a) Identify two differences between idealism and representative
realism. (6 marks)
(b) Explain and illustrate how an idealist might distinguish between ‘real’
and ‘hallucinatory’ experience. (15 marks)
(c) Assess the view that only minds and their ideas exist. (24 marks)
Specimen Paper (2000)
(a) Briefly explain the view that our senses only inform us of how things
seem. (6 marks)
(b) Outline and illustrate two arguments which might be used to support
a representative theory of perception. (15 marks)
(c) Assess the case for naïve realism. (24 marks)
23