The Philosophy Book

166

went on to counter this sceptical

point of view with an argument

that claims to prove the existence

of God, and therefore the reality of

an outside world. However, many

philosophers (including Kant) have

not found Descartes’ proof of God

to be valid in its reasoning.

Berkeley, on the other hand,

argued that knowledge is indeed

possible—but that it comes from

experiences our consciousness

perceives. We have no justification

for believing that these experiences

have any external existence outside

our own minds.

Time and consciousness

Kant wants to demonstrate that

there is an external, material world,

and that its existence cannot be

doubted. His argument begins as

follows: in order for something to

exist, it must be determinable in

time—that is, we must be able to

say when it exists and for how long.

But how does this work in the case

of my own consciousness?

Although consciousness seems

to be constantly changing with a

continuous flow of sensations and

thoughts, we can use the word

“now” to refer to what is currently

happening in our consciousness.

But “now” is not a determinate time

or date. Every time I say “now”,

consciousness is different.

Here lies the problem: what

makes it possible to specify the

“when” of my own existence? We

cannot experience time itself,

directly; rather, we experience time

through things that move, change,

or stay the same. Consider the

hands of a clock, constantly moving

slowly around. The moving hands

are useless for determining time on

their own—they need something

against which they change, such as

the numbers on a clock face. Every

resource I have for measuring my

IN CONTEXT

BRANCH

Metaphysics

APPROACH

Transcendental idealism

BEFORE

1641 René Descartes

publishes his Meditations, in

which he doubts all knowledge

apart from the knowledge of

his own consciousness.

1739 David Hume publishes

his Treatise of Human Nature,

which suggests limitations

on how the human mind

perceives reality.

AFTER

19th century The German

idealist movement develops in

response to Kant’s philosophy.

1900s Edmund Husserl

develops phenomenology, the

study of objects of experience,

using Kant’s understanding

of consciousness.

IMMANUEL KANT

According to Kant, we can only

experience time through things in the

world that move or change, such as

the hands of a clock. So time is only

ever experienced by us indirectly.

constantly changing “now” is found

in material objects outside me in

space (including my own physical

body). Saying that I exist requires

a determinate point in time, and

this, in turn, requires an actually

existing outside world in which

time takes place. My level of

certainty about the existence of the

external world is thus precisely the

same as my level of certainty about

the existence of consciousness,

which Descartes believed was

absolutely certain.

The problem of science

Kant also looked at how science

understood the exterior world. He

admired the awesome progress

that the natural sciences had made

over the previous two centuries,

compared with the relative

stagnation in the subject from

ancient times until that point. Kant,

along with other philosophers,

wondered what was suddenly being

done correctly in scientific research.

The answer given by many thinkers

of the period was empiricism. The

empiricists, such as John Locke

and David Hume, argued that there

is no knowledge except that which

I

mmanuel Kant thought it was
“scandalous” that in more than
2,000 years of philosophical
thought, nobody had been able to
produce an argument to prove that
there really is a world out there,
external to us. He particularly had
in mind the theories of René
Descartes and George Berkeley,
who both entertained doubts about
the existence of an external world.
At the start of his Meditations,
Descartes argued that we must
doubt all knowledge except that
of our own existence as thinking
beings—even the knowledge that
there is an external world. He then