Descartes (1596-1650 c.e.) and the Beginning of Modern Philosophy

Aquinas, we saw, tried to reconcile faith and reason. Aquinas began with faith and used reason to support it, so reason, for him, was subordinate to faith. Rene Descartes, our primary philosopher this week, takes a different approach. He uses reason to doubt everything.

A little historical context will help here. We are now beginning what philosophers call “Modern Philosophy.” Modern philosophy begins with the Western enlightenment. The enlightenment was a time that took the world away from a God-centered view of the universe to a reason-centered view. Many of you, I’m sure, know the story of Martin Luther (1483-1546 c.e.). He nailed a list of criticisms of the Catholic Church on its doors. It was events like these that defined this era—a diverging from the authority of the church and turn toward individual experience and exploration.

Man’s supposed place in the universe was also seriously challenged by Copernicus (1473-1543 c.e.), who put forth the idea that the sun, and not the earth, is the center of the solar system. Not only did this place less importance on earth (it’s just another planet) but it placed less importance on those humans on that earth. What are humans but some random lifeform on some random planet in some random solar system in some random universe? While most of us accept the earth as a planet revolving around the sun, try to imagine the psychological impact of that knowledge on the Western medieval world.

People continue to wrestle with the idea that humans are inconsequential aspects of an uncaring universe. When we get closer to the end of the class, a few thinkers will discuss nihilism, or the idea that existence is completely meaningless.

The optimistic attitude of the enlightenment went a long way. People thought that science and reason could help us figure out the mysteries of the universe. Consequently, reason itself was seen as more important than abstract ideas about God and the good life. Remember the distinction between metaphysics and epistemology highlighted earlier with Plato? Modern philosophy began with Descartes, who shifted the focus of philosophy from the more abstract (metaphysics) to more concrete ideas about knowledge and the way we form knowledge (epistemology).

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Descartes was philosopher, mathematician, scientist, and more. (Anyone heard of Cartesian Coordinates? See the image to the right.) He had his hand in all sorts of things. But what was common to all his interests was his rejection of any established way of doing things (like conducting experiments) and his disposition to carry out all his observations and calculations on his own. While many previous Christian philosophers wrote in Latin (the language of the scholars), Descartes wrote in his home-language of French in order to reach a wider audience.

Descartes started the school of philosophy known as rationalism: the belief that reason is the source of all knowledge. He thought a scientific method could be devised with reason as its base, as its foundation. We can learn everything through reason. Reason can reveal to us the truths about everything around us. A common phrase in philosophy, that will likely come up in other classes, is a priori. A priori means “before experience.” The opposite phrase is a posteriori, meaning “after experience.” Descartes believed that truth prior to experience is the ultimate truth. Here’s a common example of an a priori truth: all bachelors are unmarried men. Why is this a priori? Because the definition of “bachelor” is contained in the proposition, making it unnecessary to appeal to experience. It is absolutely certain that, if someone is a bachelor, he is an unmarried man.

Descartes is most famous for his method of doubt. He wanted to apply science to thinking. He wanted to doubt everything he possibly could in a mathematical way. While many previous philosophers focused on ideas and their relations to one another, Descartes felt none had focused on the thing that produces the ideas itself: the mind. By applying methodic doubt to the reasoning apparatus itself (the mind), Descartes could reach the foundation for knowledge. His method was simple: he would doubt everything he possibly could until there was nothing left to doubt. Descartes thought that anything we can possibly doubt should be rejected as uncertain. Thus anything we cannot doubt will be certain. This is Descartes’ method of doubt—to find certainty by doubting everything that can be doubted.

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Supposedly, Descartes came up with the idea for this coordinate system while lying on his back in bed and staring at the ceiling. Mathematics owes Descartes a debt for coming up with a system for placing a point on a plane.



Many of us associate the Matrix with philosophy. Well there's a reason why. There's no doubt that the Wachowski brothers (the creators of the movie franchise) studied philosophy. Check out the video below which intertwines the speech of some academics with clips from the Matrix.





Doubting Perceptions          

What if you’re dreaming right now? What if you’re dreaming that you’re reading these words for your philosophy 101 class? Isn’t it true that sometimes when you’re dreaming, you think you’re awake? Isn’t it possible that, though you think you’re awake, you’re actually dreaming? Can you really doubt the reality of the screen in front of you?

What Descartes wants you to see is that, although it may be unlikely that you’re dreaming right now, it is possible. Does this sound familiar—remember The Matrix? In the move The Matrix, Morphius asks Neo how he knows his senses aren’t deceiving him. Neo knows what his senses are telling him is real, but is that real?

Isn’t it also true that our senses deceive us all the time? Things in the distance look different than they do up close. A stick half in and half out of water looks bent, yet we know it’s straight. Here is a webpage that illustrates the deception of our senses: (

The Evil Genius (or Demon)

Descartes goes even further with his methodic doubt. He has established that it’s at least possible for our senses to deceive us. But could we be deceived about a priori ideas like 2+2=4? Can I doubt basic mathematical truths? Yes, says Descartes, if there were an evil, powerful genius who devoted himself to deceiving me. He could deceive me about all sorts of things from mathematical truths to my entire existence! (Weren’t Neo and the majority of other humans deceived about their existence in The Matrix? They thought they were living in cities and towns, but really they were hooked up to wires and electrodes.)

Now, if the evil genius were in control and hell-bent on deceiving us, is there anything we could be certain of? Yes, says Descartes. And now we reach one of the most famous phrases of philosophy: “I think, therefore I am.” This is also known as the “Cogito” since the Latin phrasing of the statement looks like this: “Cogito Ergo Sum.”

So even with the Evil Genius, Descartes can at least be certain of his existence. What Descartes means is that every time he thinks, “I exist,” he is at least certain that it is true. But what exactly is he certain of? He is certain that he is a thing that is thinking. That is Descartes’ foundation, the ultimate certain truth. He is a thinking thing.

I Can Conceive of God, Therefore He Exists

If the external world can be doubted but the mind cannot, we can see why Descartes placed so much significance on the mind. But where does he go from here? Now that he’s found a ground for certainty, what’s the next step? God. The next important issue for Descartes is God.

Descartes first establishes that he has an idea of God as a perfect being. He then reasons that, since he is imperfect, he could not possibly have an idea of perfection. Thus, God must have given him the idea of perfection. Descartes goes on to discuss what’s called “The Ontological Argument”: the idea of a perfect being entails the existence of that being. This is tricky to see at first, so think about it for a second. Part of being a perfect being, is existing—imagine a pizza with one slice missing; that slice is analogous to existence for God. God cannot be a pizza with a piece missing (this sentence probably shouldn’t be taken out of context...).

Descartes reasons further that, since a perfect being like God exists, this perfect being would not allow him to be deceived. Therefore, even though it’s possible to doubt his senses as he established, he can trust them because God exists and God would not deceive him. Sound like a cop-out for Descartes, a bad end to a good start? Many other philosophers have thought so (unfortunately we don’t have the space to go into this debate).

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Cartesian Dualism

Cartesian dualism refers to the idea that human beings are divided into two substances: body and soul. This is a view that, I’m sure, many of you take. Another view is materialism: the idea that there is no soul and that even the complex motions of our minds can be understood and explained scientifically. Undoubtedly, some of you also believe this. Notice that Cartesian dualism does not necessitate interaction between body and soul; they exist independently of each other. Thus, this view of the world allows you to study the material body while simultaneously believing in an eternal soul that lives on after the body. As we will see, however, other philosophers don’t always look kindly on this sort of dualism.

This also introduces something called the “mind-body problem.” Basically, this is the problem of how the mind or soul interacts with the body. Throughout the years there have been many different interpretations. Some philosophers try to salvage the notion of that there exist body and mind. Other philosophers try to show that there is only one substance. Some of these attempts are very complex. The Russian philosopher and mystic, P.D. Ouspensky, argued that mental processes were a special case of physical substance, so alien to the way other aspects of the physical world function that he thought it was a different phenomenon.

Another reason why Cartesian dualism continues to be so popular is that it seems to be true on introspection. When we think, it seems to us that there is this separate place where the thoughts are taking place, and it seems distinct from our bodies.

Cartesian Dualism says that there is a world of mind or soul as well as a world of physical stuff. The mind-body problem asks how these two substances interact. How does mind influence body and body influence mind? Particular answers to this question have led some to say that there is no mind at all, and only body.

Copyright © Luke Cuddy 2008