Philosophy: Descartes' Cogito Argument

(intro music)

Hi, I'm Stephan Schmid.

I'm teaching at the Humboldt
University in Berlin in Germany,

and today, I want to talk about

Descartes's famous cogito argument.

Even if you have never heard of the name

"cogito argument" before, or of Descartes,

you might have encountered
the argument itself.

It is nothing other than the
famous philosophical insight

"I think, therefore, I am,"

or in Latin, "cogito ergo sum."

This argument has become so popular

that it has even become
the subject of jokes.

Consider this one.

Descartes walks into a bar.

The bartender walks up to him and says,

"Hey, would you care for a drink?"

Descartes replies, "Hmm, I think not."

And poof!

He disappears.

Now, I admit that this
joke is probably not

the best joke ever, but
Descartes's cogito argument,

to which this joke appeals,
is definitely pretty cool.

The most exciting feature of
Descartes's cogito argument

is not the argument itself, though.

It can actually already be found

in Aristotle and Saint Augustine.

It is rather the philosophical
question that Descartes

tried to answer with it.

But who was this guy Descartes, anyway?

And what is this question
that the cogito argument

is supposed to answer?

Rene Descartes was a French
philosopher of the seventeenth century.

He was dissatisfied with
the philosophy of his time,

which was dominated by
scholastic philosophy.

The scholastics saw to
answer highly abstract

philosophical questions
mainly on the basis

of Aristotle's teaching.

Descartes was dissatisfied
with this kind of philosophy

because he considered their
highly abstract disputes

pointless and futile, and
also unable to accommodate

the results of the rising
mechanistic physics,

which sought to account
for natural phenomena

in mathematical terms.

On account of his dissatisfaction
with the philosophy of his day,

Descartes came to think

that the philosophy was in
need of a fundamental reboot,

a completely fresh start.

This is surely a nice idea,

but how do you build a
new philosophical system?

Well, maybe it's just in
a way we usually build

new and stable things, such
as houses and monuments:

just by building them up on a
strong and stable foundation.

Yet, what would serve as an
appropriate firm foundation

upon which to build a
new philosophical theory?

Descartes was convinced that
nothing could do the job

better than our most certain beliefs

that is, the things that we
can really be sure are true.

Let us now finally turn
to Descartes's attempt

to establish a firm foundation
for his new philosophy.

He carries out his attempt
most extensively

in his "Meditations On First Philosophy."

As we said, he wants to
find absolutely certain

and unshakable beliefs that he can build

his new philosophy upon.

The method that Descartes suggests

has become known as
"Descartes' radical doubt."

The main idea is to
subject all our beliefs

to radical doubt, and
then see which of them

can withstand such doubt
and hence be accepted

as absolutely certain.

As the application of this method reveals,

there is indeed a huge
difference between the things

that we in fact take
ourselves to be certain about

and the things we may justifiably do so.

Just consider the following examples.

You're doubtlessly pretty certain

that you're watching a video right now,

or that you have brushed
your teeth this morning,

or that two plus two equals four.

Yet are you really justified
in being so certain?

Descartes thinks that after
having employed his method

of radical doubt, you will
have to admit that you are not.

Indeed, there are only very few beliefs

that pass Descartes's
test of radical doubt.

Can you be really certain

that you are watching a video right now?

No, you cannot.

After all you could just
as well be dreaming.

The same holds about your beliefs

that you brushed your teeth this morning.

And most shockingly, perhaps,
not even mathematical beliefs

escape Descartes's radical doubt,

for how can we be sure that two plus two

equals four, say?

True, we have often convinced ourselves

that we get a collection of four objects

if we unite two collections
of two objects,

but what ensures that we
did not err every time

we convinced ourselves of this?

Perhaps there is an evil demon,
or a wicked neuroscientist,

who constantly manipulates our thoughts

by systematically distracting
us when we try to verify

our mathematical beliefs.

As these considerations show,

Descartes's method of radical doubt

leaves hardly any belief unaffected.

But there is hope.

Descartes argues that
there is at least one thing

that we cannot doubt and which we can be

absolutely certain about.

This is the fact that when we doubt,

we cannot doubt that we doubt or think,

for doubting is just a form of thinking.

But when we can be sure that we think,

we can be equally sure that
we exist while we are thinking,

for if indeed we can be
sure that we are thinking,

there has to be something
that does the thinking,

and we are the something, you and I.

It is, hence, here that we finally arrive

at Descartes' famous cogito argument,

"I think, therefore, I am."

The cogito argument then
assures us of the fact

that there is at least one thing

that is impossible to doubt

and is thus absolutely certain.

This is the fact that
we exist while we think.

And this is precisely
the unquestionable fact

that can figure as the
unshakable and firm foundation

which Descartes has been looking for

in order to build his new
philosophical system upon.

The prospect of building
a whole world view

upon the certainly that
we exist while we think

must strike you as not very promising.

Given that we can only
be certain that we exist

while we think, how can
we ever know, as we seem to,

that we live on a planet
we share with human beings

and other animals and
which orbits the sun.

And how can you know that
two plus two equals four,

or that you are watching a video?

It is indeed a long road
for Descartes to restore

our certainly in our common sense beliefs,

and many of these beliefs have
to be abandoned along the way.

Amongst those are our
commonly accepted beliefs

that materials things are really colored

or have other sensory
properties like tastes,

smells, and sounds.

It takes Descartes the whole
rest of his six meditations

to walk down this road
and restore our confidence

in our beliefs of mathematical truths

and the existence of the outer world.

It would take us hours to
carefully reenact all the steps.

However, in order to get a rough grasp

of Descartes's procedure,
it will be worthwhile

to reconstruct just one
step that Descartes takes

in order to extend the stock of beliefs

that we can justifiably be certain about.

The method Descartes employs for extending

our certain beliefs
consists in squeezing out

the certainties he has already arrived at.

Actually, we have already
encountered this method,

for Descartes's cogito
argument is such a way

of squeezing out a certain
belief or idea from another.

After all, the cogito
argument is an argument,

that is, a transition or an inference

from one belief to another.

The unshakable belief that
this argument starts out from

is the belief that we are
thinking when we are doubting,

and we arrive at this
certainty just by observing

that whatever we might
doubt, we cannot doubt

that we doubt when we doubt.

Now, the cogito argument
takes this certainty

and squeezes out the new
certainty that we cannot

only be sure that we think when we doubt

but also that we exist when we think.

And it is exactly this
newly gained certainty

of our existence which the
cogito argument provides us

that Descartes squeezes next.

In a famous passage of his
second meditation, he writes,

"I am, I exist - that is certain.

"But for how long?

"For as long as I am thinking.

"I am, then, in the strict sense only a thing

"that thinks; that is, I
am a mind, or intelligence

"or intellect or reason.

"But for all that, I am
a thing which is real

"and which truly exists.

"But what kind of a thing?

"As I have just said - a thinking thing."

As becomes plain here, Descartes
immediately squeezes out

further information about his nature

from the certain belief that
he exists while he thinks.

As a result, Descartes cannot
only know with certainty

that he exists, but also
that he is a thinking thing,

a thing capable of thinking.

This is still not a lot, though.

At this stage, Descartes can
only be ensured of the fact

that he is a thinking thing,

and it is still an open question
whether he also has a body,

as we usually suppose.

If you are puzzled now, or even afraid

that you cannot know whether
you really have a body,

that you really are watching this video,

or that you really have brushed
your teeth this morning,

the only comfort I can give you

is that Descartes at least
thought that it can be proved

that we can be certain that we have a body

and that our senses, by
and large, assure us

of the existence of other
corporeal things, even

though they systematically
deceive us about their nature.

And this can be proved by further
squeezing out our clear

and distinct idea of
ourselves as a thinking thing.

If this promise is not
enough to give you comfort,

then there is only one
last advice I can give you.

Go and get a copy of Descartes's

"Meditations On First Philosophy,"

and start reading his third meditation.