Think: A Compelling Introduction to Philosophy (33 page)

COLOURS, SMELLS, SOUNDS,
FEELS, AND TASTES

Here is Descartes's great contemporary, the physicist Galileo
Galilei (1564-1642):

Now I say that whenever I conceive any material or corporeal
substance, I immediately feel the need to think of it as
bounded, and as having this or that shape; as being large or
small in relation to other things, and in some specific place at
any given time; as being in motion or at rest; as touching or
not touching some other body; and as being one in number, or
few, or many. From these conditions I cannot separate such it
substance by any stretch of my imagination. But that it must
he white or red, bitter or sweet, noisy or silent, and of sweet or
foul odor, mny mind does not feel compelled to bring in as
necessary accompaniments. Without the senses as ourguides,
reason or imagination unaided would probably never arrive
at qualities like these. Hence I think that tastes, odors, colors,
and so on are no more than mere names so far as the object in
which we place them is concerned, and that they reside only in
the consciousness. Hence if the living creature were removed,
all these qualities would be wiped away and annihilated.

Galileo is here expressing what has become called the distinction
between the primaryand the secondaryqualitiesof material things.
The secondary qualities are the immediate objects of the senses:
colours, tastes, sounds, odors, feels. According to Galileo they'hold
their residence' only in the sensitive (i.e. perceiving) animal. Moreover, according to Descartes, there is no reason for supposing them
to `resemble' whatever in nature causes them-the arrival of photons at the eye, in the case of colour, for example.

Descartes similarly had a poor view of the senses as vehicles of
truth (remember the ball of wax in Chapter i):

For the proper purpose of the sensory perceptions given me by
nature is simply to inform the mind of what is benficial or
harmful for the composite of which the mind is a part ... but I misuse them by treating them as reliable touchstones for immediate judgments abut the essential nature of the bodies located outside us.

An example he liked was the perception of a pain as being in the
foot, after the'animal spirits' had conducted their energy, their'jet
of flame', up the nerves and into the brain. God devised it that the
mind receives the best sensation that it could (God's good pleasure, again). The particular motion of the brain could have conveyed something else to the mind. However, there is'nothing else
which would have been so conducive to the continued well-being
of the body'. In other words, if God had brought it about that I interpreted the motions in the brain as, for instance, just signalling a
perturbation of my brain, then I would be slow to move my foot,
which is being injured, out of harm's way. We might notice that
Descartes's position here contains a denial of epiphenomenalism.
It is because the mental events are one thing or another that we
move our foot quickly. If the mental were inert, God could let it fall
out however he wants without affecting our well-being.

I)escartes's quaint language conceals a surprisingly modern
point. If we substitute evolution for God, we can put it like this. For
a creature to flourish, it must get information from the environment that tallies with its actual needs. All that is necessary for this
is that the information stimulates it to action in the right way. For
instance, if a predator is coming, it needs some information that
stimulates flight. However, for this function, it does not matter
what experience it gets. If the predator treads on a twig, then the
`motions' this induces in the ear could result in the creature hearing a loud sound, or a discordant sound, or a harmony, or a high pitch, or a low pitch, or they could result in just a bad smell, but so
long as it senses something that frightens it, its senses are doing
their job. The senses provide us only'confused' (as opposed to clear
and distinct) data.

This also lets God off the hook. If we ask why the senses sometimes deceive us, making us think that colours lie outside us when
they do not, then the answer conies in two parts. First, he created
the'best system that could be devised' for producing a sensation
especially conducive to the preservation of the healthy person. The
senses, as we have seen, can deceive us. But Descartes insists that it
is we, not nature or God's design, who are at fault if we misinterpret
the data of the senses, uncorrected by use of intelligence. We
should not treat the data of the senses as straightforwardly conveying information about the real properties of things.'I'his would be
to treat confused data as if they were clear and distinct.

When we do use our intellects, abstracting away from the data of
the senses, what kind of world are we left with? Descartes, the
mathematician, believed that the real property of'res extensa' was,
as the name suggests, spatial extension. Everything else was the
possibly illusory, sensory 'filling' of spatial volume by things like
colours and feels-things that, like Galileo, he believed to have
their real residence only in the mind. So as well as opening up dualism of mind and body Descartes and his contemporaries open up
a dualism between the world as it is for us (sometimes called the
'manifest image')-the coloured, warn, smelly, noisy, comfortable, familiar world-and the world as it is objectively or absolutely (the `scientific image')-the world that contains nothing but physical particles and forces spread out across the boundless
spaces of the cosmos.

Why is science thought to drive colours and the rest into the
mind? The most compelling argument seems to be one from perceptual relativity. People are apt to think of `relativism' as a particular threat, or temptation, in moral philosophy, where we are
uncomfortably familiar with the way situations strike different
people differently. But a more general relativism is here raising its
head. We can present an argument from relativity concerning
tastes, odours, colours, sounds, and `feels' like this:

Suppose a part of the world or an object in the world displays a certain smell, etc. to one observer O. How it smells,
etc. will be a function of O's particular sensory structures.
So, there will be or could be another creature O' with different sensory structures, to whom the same part of the
world or the same object would smell, etc. quite differently.
0 and O" may each live equally efficient, adapted lives. So,
there is no reason for saying that just one of 0 or O' has got
the smells, etc. right. So, there is no one correct distribution
of smells, etc. in the world. So, smells, etc. are better thought
of as entirely mind-dependent.

This argument was familiar in the ancient world, before returning
to prominence in the seventeenth century. There are a number of
points to notice about it.

First, it does not depend on the actual existence of the different
creature O". It is enough that we can see how there could be such a
creature: one whose colour receptivity is quite different, or whose
auditory apparatus sensitizes it to different frequencies of sound, or to different kinds of energy altogether. Of course the argument
becomes more graphic when we come across striking instances.
Nobody who keeps a dog can believe that the world of smells that
dogs inhabit hears much resemblance to our own. And some of us
can remember, for instance, how differently beer or dry wine first
tasted before we got used to it. Different sensitivities clearly exist:
for a start, all mammals except some primates are colour-blind.
There are substances (phenol thio-urea is an example) that have a
pronounced bitter taste to a high proportion of human beings, but
no taste at all to others. And so on.

But quite apart from such actual cases, we can easily see how
there could be forms of life that get by perfectly well with quite different sensory `fillings: Some people tune their TV sets so that the
colours seem garish and glaring to others, but they see the same
scenes as a result.

The second premise too seems incontestable. It represents a
piece of knowledge we have about the world. We know that certain
kinds of condition, for instance, can lead us to taste things very differently. With colds, we lose much of our sense of smell. We know
a good deal about how colour vision depends upon the particular
sensitivities of three different kinds of receptors in the eye, as described in Chapter 2. We know that bats navigate by acoustic
means that are closed to us.

So the initial conclusion seems inevitable. Compare this: two
different television sets may receive the same signal. However,
what picture appears depends on the particular structure of the
television. Hence, there could he televisions that deliver different
outputs from the same signal (and of course there are).

The next premise is crucial, and one that is often forgotten in
discussions of relativism in other areas, such as ethics. Any argument aiming at something like the final conclusion needs to go via
this. It is no good just pointing out that different creatures perceive
the world differently, if that allows the interpretation that just one
set of them has got the world right. The analogy with the televisions
makes the point. Sure, someone might say, the way in which a television set shows a picture in response to a signal may vary. If the
television is the wrong kind for that signal, then it just shows snowstorms, for instance. But that just means that the television misses
information that exists, that is objectively there, carried by the signal. It is no kind of argument that the information is not really
there, independently of the receiver, in the first place. If the transmitter is beaming the inaugural speech, a television showing a
snowstorm is doing worse than one showing the speech. It is not
doing just as well, but in a different way. But that is what this argument from relativity is aiming to show. So, there is a hole in it.

There would be if it were not for premise that the different creatures might live equally well-functioning, adapted lives. This plugs
this gap, by asking us to see the different observers as potentially
equally well adapted to their worlds. For Descartes, that would
have been a belief with theological backing. For us, it may have an
evolutionary explanation. Creatures that cannot receive the kind
of information they need to live their lives die out. So, unlike the
televisions, 0 and 0* may be doing as well as each other, but living
lives with different sensory experiences: seeing, smelling, hearing,
tasting, and feeling differently. It is this equality that suggests, as Russell later put it, that it would he `favouritism' to say that the
world is better represented in one of these ways than in any other.

The premise about equal adaptation may not be enough however. We may want to think like this. Certainly, dogs, for instance,
are adapted creatures, with sensory systems that meet their natural
needs. But let us distinguish the different dimensions of sensory
experience. Dogs have marvellous noses. So, let us admit that they
can smell smells that we cannot. They are the `authorities' on the
distribution of smells. On the other hand, dogs are colour-blind.
Therefore, they are not `authorities' on the distribution of colours.
We can make finer visual discriminations amongst objects in a
whole variety of different lights than dogs can. That is what our
colour vision is for. So why not say that the real colours are the ones
that the creatures best adapted for colour see? And the real smells
the ones that creatures best adapted for smell sense? And if we can
say this, then the subsequent conclusions will not follow.

This certainly points to a hole in the argument as it is stated. To
repair the hole we would need some stronger premise. A repair that
would do the job might he to aim for each sensory dimension D
(vision, touch, smell, sound, taste), one at a time. There would he
five different arguments, and in each of them the crucial premise
would read:

O and O" may each live equally efficient, adapted lives in
respect of sensory dimension D.

If this is accepted, the rest of the argument looks like plain sailing.
The rationale for the final move is obvious enough. Consider phenol thio-urea. It cannot in itself be both tasty and tasteless. Simi larly, the world cannot be thought of as containing as many smells
as there are possible sensory apparatuses, adapted for registering
just some molecules (or their absence) in some combinations and
concentrations. Such a world would contain an infinite number of
coexisting smells, since there is no limit to the possible varieties of
detector.

The upshot of the argument is called `secondary quality idealism'. It gives us Galileo's result that the qualities that are the immediate objects of sensory experience are driven `back into the mind'.

GOOD SOLID SENSE