PHILOSOPHY - Metaphysics: Paradoxes of Perception [HD]

In this video, Dr Eugen Fischer (UEA) presents the ‘argument from illusion’. This argument appears to refute our common-sense conception of perception (seeing, hearing, etc.). Together with parallel arguments, it raises the problem of perception that has been a lynch-pin of Western philosophy, since the mid-18th century.

(intro music)

Hi! I'm Eugen Fischer, senior lecturer in

philosophy at the University of East Anglia.

Today, we will look at some
paradoxes about perception,

known as "arguments from illusion."

These arguments ask us to consider
cases of non-veridical perception,

where something appears
different than it is.

For example, when we look at round
coins sideways, they appear elliptical.

Similarly, when seen from a
greater distance, a man may

seem less than half as tall as another
man of roughly equal height.

Or consider the phenomenon
known as "refraction."

When a straight straw is partially

immersed in water, it looks bent.

All of these facts are
familiar from daily life.

None of them is normally contested.

But these familiar facts seem to
have a striking consequence.

They seem to imply that
we are cut off from the

physical objects around us by
a veil of experience within us.

The eighteenth-century philosopher David
Hume drew this consequence very swiftly

when reflecting on another relevant fact:

as we all know, the table look
smaller and smaller to people

the further away the move from it.

Hume observes that the
table we see seems to

get smaller as we move away from it, yet
there is no change in the size of the

real table, which is made of wood and
stands in the parlor, regardless of

whether we look at it or not.

Hume immediately infers that
we cannot be aware of this

unchanging, real table, and therefore
must be aware of something else.

He concludes that thing we
see is an image of the table,

whose size does change as we
move away from the table.

This image then is present
to us in our minds.

In other words, when you look at the table,

you are only aware of a mental
image, not of the physical table.

To unpack this rather swift but
historically influential argument,

let's have a closer look at the case of

the round coin that appears elliptical
to you when you look at it sideways.

What exactly are you
aware of in this case?

Describe your experience, rather
than the objects around you.

Describe what you are aware of,

without making any judgment about the
physical object you're facing, without

judging that object's shape, or size,

or color, or any other
property of it.

That the right thing to
say then, it seems,

is that you're aware of an
elliptical, golden patch.

This judgment is often called
the "phenomenal judgment."

The first step the argument elicits such

phenomenal judgments about cases of

non-veridical perception, like that
of the coin or Hume's table.

The second step has us figure out what
kind of thing we're then aware of.

What could that elliptical patch be?

It cannot be the coin, because the
coin is round and not elliptical.

So you're clearly aware of
something other than the coin.

Hume called this other thing an "image."

A now more common, and more
neutral term, is "sense-datum."

Now continue to look in
the direction of the coin.

How many different things do you see?

How many different things
can you direct your

attention at and say
that you are aware of?

Clearly, you cannot first direct your
attention at something elliptical and

then shift your attention elsewhere to

become aware of something
else that could be the coin.

So you are aware only
of one thing, not of two.

We already concluded that you
are aware the sense-datum.

Therefore, you cannot be
aware of the coin too.

At any rate, not in the same way or sense.

But of course you are aware
of the coin in some sense.

You know perfectly well that you are

looking at a coin rather than,
say, a marble or a dice.

Proponents of the argument from illusion
therefore commonly called the cautious

conclusion that the subjective sense-datum
is the only thing you are directly aware of

when looking at the coin sideways.

At the same time, you may be indirectly

aware of the physical object, namely,

in virtue of being directly
aware of the sense-datum.

So far, we have rehearsed the
first half of the argument.

The second half then generalizes from
the particular case of non-veridical

perception to all cases of perception.

This generalizing step builds on the

observation that sense data and physical

objects are the most radically
different kinds of things.

For a start, the sense-datum is
rather less stable than the coin.

The color patch changes its
shape the moment you move,

while the coin retains its shape.

The sense-datum also vanishes the moment
you close your eyes, while the coin vanishes

only the moment it gets melted down,

or some other major physical
mishap occurs to it.

So the sense-datum and its properties
depend upon you, the observer,

in ways in which the physical
object and its properties do not.

Sense data are subjective, ever-changing,

and fleeting, like the flickering
of a candle or its dying smoke.

Physical objects, by contrast, are

objective and stable, like
solid tables and hard coins.

the intuitive key assumption now is

that our awareness of such radically
different things should

constitute qualitatively
different experiences.

We should be able to tell from
the subjective quality of our

experience whether we are aware of a
sense-datum or of a physical object.

But compare.

Have a look at this pencil, which
is partially immersed in water.

To most people, it seems bent.

If you are like them, you are now directly

aware of a sense-datum or color
patch, which actually is bent.

And now look at the pencil in the dry,

when it looks as straight
as it actually is.

Can you tell any difference between the

subjective quality of one
experience and the other?

Does one scene look, say, follier to
you, or less clear, or more vivid?

Philosophers who find they cannot grow
aware of any such difference like to

conclude that we must be aware of
the same kind of thing in both cases.

So, if we are directly aware
of a subjective sense-datum

in the case of non-veridical perception,

such a sense-datum is what
we are directly aware of

also in the case of veridical perception.

When we use our eyes, all we are ever

directly aware of are
subjective sense-data.

By sight, we are never directly
aware of physical objects.

As we look around ourselves, we are cut

off from the physical objects
in our environment

by a veil of subjective sense-data.

Other variants of the argument establish

analogous conclusions about the other
senses: hearing, smell, taste, and touch.

Some other arguments, including
arguments from hallucination,

lead from different premises
to the same conclusions.

These conclusions seem to
clash with common sense.

Surely, when we look at tables and
chairs, we see these public, stable,

physical objects without further ado.

Surely, these objects are not blocked

from view by subjective, ever-changing
objects of awareness.

Surely, we can just see tables and chairs,

without having to infer their
presence around us from

subjective images, sense-data,
or what have you.

By leading to a conclusion that clashes
with our common sense conception

of perception, all these arguments

confront us with what is often simply
called the "problem of perception."

We don't doubt that things sometimes

appear elliptical, yellow,
bitter, or rough

when they actually are round,
white, sweet, or smooth.

The present argument suggests

this implies that we cannot just see

or hear, smell or taste, or
feel the things around us

This raises the problem: how is it
possible for us to just see, or

otherwise perceive, the things
in our physical environment

if these things often appear
different than they are?