8/11/2019 Descartes Lesson 3

1/2

1

The Cogito

1. In the First Meditation, everything that Descartes believed was cast into doubt. He supposes

that he does not exist, that his memory is faulty, that he has no senses, no body, that

extension, movement and place are mistaken notions. For Descartes to build his new system

of connected propositions, however, it is necessary that he finds at least one indubitable

proposition, which can serve him as the premise for his system. If he cannot find an

indubitable premise, then he will conclude that nothing is certain.

2. The ancient mathematician Archimedes observed that with a sufficient long lever and a fixed

point off the Earth, he could move the entire globe. Similarly, Descartes reasons, that if he

could find one single indubitable proposition, he would be able to rebuild a new edifice of

knowledge.

3. Descartes concludes that if there is a demon that is employing all his power to deceive him,

he must necessarily exist. In the second Meditation he says

But had I persuaded myself that there is no sky, no earth, no mi nds or bodies; was I not,

therefore, also persuaded that I did not exist? No indeed; I existed without doubt, by the

fact that I thought at all. But there is some deceiver both very powerful and very cunning,

who constantly uses all his wiles to deceive me. There is therefore no doubt that I exist, if

he deceives me; and let him deceive me as much as he likes, he can never cause me to be

nothing, so long as I think I am something. So that, after having scrupulously examined

everything, one must then, in conclusion, take as assured that the proposition: I am, I

exist, is necessarily true, every time I express it or conceive of it in my mind.

4. The argument Cogito ergo sum,(I think, therefore, I am) encapsulates Descartes cogito

argument. However, this argument does not appear in the Meditations (it appears in the

Discourse on Method, written in French, and in the Principles of Philosophy, written in

Latin). In the second Meditation Descartes simply says I am, I exist. Why? TheargumentI think, therefore, I am is a syllogistic reasoning based on two premises:

a. Everything that thinks exists.

b. I think.

c. Therefore I exist.

8/11/2019 Descartes Lesson 3

2/2

2

In the first meditation Descartes had cast everything into doubt. The above argument,

assumes, at least, that the proposition If something thinks, then it exists is true. But

accepting the above proposition as true would breaching the basic rule of his method of

doubt (that nothing should be assumed as true) established in the first Meditation.

5. In his replies to the objections of the Dutch theologian Caterus, Descartes distinguishes

between two operations of the mind inferring something, and knowing it through a simple

intuition of the mind. In this respect, he says:

Now, the dialecticians [= specialists in applied logic]dont usually call awareness of

first principles knowledge.And when we take in that we are thinking things, this is a

basic principle that isnt arrived at through any syllogism.

When someone says I am thinking, therefore I am, or I exist,he isnt inferring existence

from thought by means of a syllogism; rather, a simple intuition of his mind shows it to

him as self-evident. If he had been inferring it through a syllogism, it would have been

this: Everything that thinks is, or exists; I think; therefore I am, or exist. And for this he

would need already to have known the first premise Everything that thinks is, or exists;

but what actually happens is that he learns it by experiencing in his own case that it isnt

possible to think without existing. Constructing general propositions on the basis of our

knowledge of particular ones is something that we just naturally do.

6. If one accepts Descartes distinction between an inference and an intuition of a self-evident

proposition, another problem pops up: is he justified in concluding that an ego, an I exist?

Or perhaps he should have said, thought exists? The eighteenth century German

philosopher Georg Lichtenberg was of this opinion.