A tree falls in a forest but there is no one to hear
it, does it make a sound?
An Introduction to Perception
• Epistemology is the theory of knowledge i.e. how do we know
what is real or not real?
• We will focus on three theories of perception:
– Direct Realism
– Indirect (or Representative) Realism
– Idealism.
How we become aware of, identify or know something.
Imagine you met an alien who does not perceive the
frequencies of light as we do. Instead the alien perceives
a whole set of higher ones, such as ultra violet and
beyond. The alien represents these waves in a range of
colours just as we do.
In pairs discuss:
Who sees the true colours of
the world: humans or aliens?
But if neither does, does
that mean that no colours
are the real colours?
Thinking questions……
• Do you think your favourite food tastes the
same to a dog as it does to you?
• Do you think dog food tastes the same to you
as to a dog?
• Who has a truer perception of the world: dogs
or humans?
Realism vs Idealism
Central question in debate on perception:
How much of what we perceive is really a feature of
the external world, and how much is a feature of our
minds?
2 theories on this:
– Realism: At least some of what we perceive is a feature of
the external world, & exists independently of our minds.
– Idealism: None of what we perceive is a feature of the
external world: it is all just a feature of our minds.
Consider whether the object or topic is real or not. For this
exercise take ‘real’ to mean ‘has an existence independent of
minds – human or otherwise’.
REAL
Numbers i.e. 5,6,7
Your reflection in a mirror
Colours i.e. blue
Smells
Morality
Electrons
Scientific laws e.g. law of gravity
Ghosts
Matter i.e. what makes up the material
universe
Beauty
NOT REAL
DON’T KNOW
Two forms of realism
• Direct Realism (aka ‘common-sense’ or ‘naïve’ realism):
– We see things in the external world immediately and directly.
– We don’t see them by seeing anything else.
What does this mean?
All objects are composed of matter: they occupy space, have properties
such as smell, texture, size etc. We perceive these properties directly.
Therefore the senses provide us with direct awareness of the external
world! These objects continue to observe the laws of physics & retain their
properties whether or not there is present anyone to observe them doing
so.
A tree falls in a forest, but no one is there to witness it. Does it
make a sound according to direct realism?
• The naïve realist theory may be characterized as the acceptance of
the following five beliefs:
• There exists a world of material objects.
• Some statements about these objects can be known to be true
through sense-experience.
• These objects exist not only when they are being perceived but also
when they are not perceived. The objects of perception are
largely perception-independent.
• These objects are also able to retain properties of the types we
perceive them as having, even when they are not being perceived.
Their properties are perception-independent.
• By means of our senses, we perceive the world directly, and pretty
much as it is. In the main, our claims to have knowledge of it are
justified."
Two forms of realism
• Indirect realism (aka representative realism):
– We see things in the external world indirectly, by seeing mental
representations of them.
– When I look at a table, I see the appearance of it – a mental image,
which represents it to me.
– Philosophers call this mental image a sense datum (sense data).
– Indirect realists say that we see physical objects by seeing their
sense data (just as we might see a celebrity by seeing their image
on a TV screen).
For the indirect realist, there is a distinction between the way the object
appears to the observer and the object as it is in reality. Sense data or
sensations are a representation or image of the world.
It’s as if we had pictures in our minds which represent to us the real world
outside of our minds.
In simpler terms….
Both claim that the physical world exists independently of
perceivers and that the world is as science says it is.
But…..
• Direct realism claims that what we perceive is really the
external world.
Whereas….
• Indirect realism claims that what we immediately or
directly perceive are sense-data , rather than the physical
world itself, which can only be perceived indirectly.
Crux of the matter: they disagree over whether we perceive the
properties of matter directly and as they are.
Activity
• Draw a diagram, using words/lines/
pictures etc., to illustrate the difference
between the direct and indirect realists’
theories of how we perceive physical
objects.
Three illusions
1. The thumb and the moon:
– If you hold your thumb up to the moon, your thumb looks
bigger – even though it obviously isn’t.
2. The rose under sodium light:
– Under sodium street lamps, a red rose will look grey,
even though it hasn’t changed colour.
3. The stick in water
– If you half-submerge a straight stick in water, and
look at it from the side, it looks bent, even though
it isn’t.
Activity
How could someone use these 3 illusions to
argue against direct realism?
• Set your argument out in ‘standard form’
The argument from illusion - 1
One way of stating this:
P1. If direct realism is true, then the world must
always be exactly the way it appears to us.
P2. The 3 illusions show that the world isn’t always
exactly the way it appears to us.
C. So the 3 illusions show that direct realism is false.
The argument from illusion - 2
Another way of stating it:
P1. When I look at a stick in water, I see something
that is bent.
P2. The bent thing cannot be the stick itself.
IC.
So it must be a mental image of the stick – a
sense-datum.
C.
But this means I see the stick indirectly, by
seeing its sense-datum – in which case
direct realism is false.
Brainstorm the strengths and
weaknesses of direct and indirect
realism.
Put down as many as you can – be
speculative!
What do you see?
• Read Bertrand Russell’s Chp 1 (pp 1 - 4).
Answer the comprehension and evaluation
questions.