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C H A P T E R  15

R e n é  D e s c a r t e s

Modern Philosophy



René Descartes   





René Descartes L’homme





R e n é  D e s c a r t e s

  ( 1596 - 1650 )


He was born in La Haye France.

He studies Scholasticism and law at La Fleche - a Jesuit college.

Descartes invented analytic geometry.

Did some work in optics and science.

In 1633 Galileo was condemned for supporting Copernicus.

Descartes moved to Holland to avoid condemnation in 1629.

He wanted to support Galileo's theory of indirect realism.

This theory has a problem:

Material objects are perceived indirectly by ideas.

We can never compare our ideas with physical objects.

We can not know that our ideas resemble physical objects.

He wanted to persuade the church to accept modern physics.

Cardinal de Berulle tells him it's easier to do it with Augustine.



Augustine's method begins with doubt.

The senses cannot obtain absolute truth.

I doubt, therefore I exist.

This truth is certain and eternal.

I cannot be the author of an eternal truth, for

the effect cannot be greater than the cause; therefore,
God exists.


In An Historical Introduction to Philosophical Thinking, Perelman says:  

The idea of literary property is in fact a modern one; until the time of the romantics the truth of an idea was more important than its originality. Novelty was a sign of error, and therefore no one was afraid of Plagiarism. On the contrary, it was better to present a new idea as a form of a very old one, (86).


Descartes became the tutor to the Queen of Sweden.

He died of pneumonia in 1650.



CH. Perelman, Trnaslated by Kenneth A Brown,  An Historical Introduction to Philosophical Thinking, Random House, New York.




1). The foundation of knowledge is certainty.
     Certainty is what is impossible to doubt.
     Check all beliefs by examining their foundations.

2). We can doubt our senses.
     Distant things,
insanity, dreams, and memory are unreliable.
Wax Example

3). We can doubt our inferences.
     I could be insane.
     There could be an
Evil Demon deceiving me.

4). But if I doubt, then I exist.
     I think therefore I am; Cogito Ergo Sum is an inference.
     All inferences can be doubted because of #3. (see above)
     I think, I am. This is an identity statement. (I think = I am.)
     This is self evident, clear, and distinct.

5). Only God could cause my concept of God.

6). Experiences are accurate representations of reality.

7). Physical objects are different from minds.
     Color, odor, taste, and texture don't belong to matter.
     Extension, movement, shape, and location belong to matter.
     Minds are self-moving, thinking, not extended, or in a place.






If I can't think of something as divided, then it's not extended.

I can't think of mind as divided; therefore, mind is not extended.



If I cannot think of something as divided, then it's either not an extended thing, or it is an infinitely extended thing.

Mind cannot be thought as being divided; therefore, mind is not an extended thing, or it's an infinitely extended thing.


1.         (X) {~Tx > [ ~Ex V Ix ]}

2.         ~Tm            /            ~Em V Im





1. If wax is understood, then it's understood by our senses or (imagination or judgment).

2. Wax is understood.

3. It is not understood by our  senses.

4. It is not understood by our imagination. / Therefore

5. Wax is understood by our judgment.


1. W > [ S V ( I V J ) ]

2. W

3. ~S

4. ~I         /         J

5. S V ( I V J )      1, 2 mp

6. I V J                3, 5 ds

7. J                     4, 6 ds


To demonstrates the limitations of our senses with his wax example. Consider a piece of wax; your senses detect a color, smell, taste, texture, sound, and so forth. All these properties change, when introduced to heat. By what faculty do we know that this is the same object? Certainly not the senses. You can imagine infinite changes. Descartes concludes:

“ And so something which I thought I was seeing with my eyes is in fact grasped solely by the faculty of judgment which is in my mind."




Meditations on First Philosophy

Discourse on the Method of Rightly Conducting One’s Reason and of Seeking Truth in the Sciences



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