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  • (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.

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PHILOSOPHY - 歴史。デカルトのコギト論争 [HD] (PHILOSOPHY - History: Descartes' Cogito Argument [HD])

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    耀梅林 に公開 2021 年 01 月 14 日
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