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Alex Peak

René Descartes


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“René Descartes” may look like an odd name.  Because the name is French, the pronunciation is different from how we pronounce things in English.  The correct pronunciation of his name is “reh-NAY day-KART.”


Descartes, who lived from 1596 to 1650, is often called the “Father of Modern Philosophy.”

In addition to being a philosopher, René Descartes was a scientist and mathematician during the Renaissance period.  He is famous for saying “Je pense donc je suis,” which is French for “I am thinking, therefore I exist.”


Descartes wanted to know how we know things.  How, for example, do you know you are sitting in front of a computer and reading this web-page?

You can see the computer with your eyes.  You can reach out and touch it with your hands.  Maybe you can even hear the hum of the computer with your ears.  However, this wasn’t enough for Descartes.  For example, you could be asleep, and only dreaming that you are reading this web-page.

So, Descartes asked himself if there are any things that remain real whether he was awake or not.  He concluded that although he might only be dreaming that he is doing this or that activity, mathematical principles remain the same.

For example, whether you are dreaming or awake, a square always has four equal sides and a circle is always round.  Whether you are dreaming or awake, you know that 2+2=4.

Still, Descartes was not satisfied.  For he asked himself, “What if there is an silly dæmon who is just tricking me into thinking that squares have four equal sides?  What if this silly dæmon is also tricking me into thinking that 2+2=4?  What if circles don’t really exist at all, and the silly dæmon is just tricking me into thinking they do?”

Descartes was in a jam.  Could he prove anything at all?

Then Descartes had an idea!  He decided there was something he could prove to himself.  He decided that he had proven to himself that he, René Descartes, must exist!

How did he come to this conclusion?  He decided that even if it were true that some silly dæmon were tricking him into believing things that weren’t true, he himself at least had to exist.  After all, if he didn’t exist, there would be no one there for the silly dæmon to trick!

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