Key Concepts of the Philosophy of René Descartes

Updated on February 10, 2017

René Descartes was a 17th century French mathematician and philosopher who is now considered the father of modern philosophy. As a mathematician, Descartes is responsible for the Cartesian coordinate system and as a philosopher he moved the concerns of the medieval philosophers, which were chiefly concentrated on theology, forward toward a philosophy that had interests that went outside the church. This is sometimes overlooked by modern readers of Descartes because so much of his work is interested in ideas such as the existence of God and the presence of a soul that obsessed other philosophers before him but unlike the medieval theologians, Descartes did not take the existence of God or the soul for granted. He instead developed a complex metaphysical system that forced every major philosopher until at least Kant to respond to it.

Descartes is credited at beginning the school of thought called rationalism which asserted that there was important knowledge that could be gained without the senses through reason alone. As a mathematician, Descartes would use the rules and language of math as examples of how this was true. His philosophy is a response to the skepticism that he saw becoming prominent after the scientific advancements of the enlightenment. Some have contended in recent years that Descartes was not in fact a Christian, or more accurately, that he was a believer in God but had a radically different idea of God than that of mainstream Christianity. I cannot say for certain whether this is true but Descartes did spend a big portion of his life examining cadavers looking for the soul, something that seems to indicate belief in the soul but being in opposition to Christian views of the time that considered such practices blasphemy.

Cartesian Doubt

Descartes begins his Meditation on First Philosophy by “doubting everything there was to doubt.” The purpose of this exercise was to strip away all knowledge that could possible held in doubt as genuine in order to arrive at something that could be determined to be known at absolute certainty. Descartes determines that because his senses can be fooled, he has no reason to believe in the findings of science, the existence of the external world or even that his own body exists. He postulates that reality may be a dream and that he would have no way of knowing whether he was dreaming.

Descartes also uses a thought experiment called the “evil demon” (sometimes evil genius or other phrases are used for the concept) which consists of a being that exists only to fool his senses. Descartes uses other analogies, such as a piece of wax that changes shape to appear to be something different but remains a piece of wax and of people walking across the square that he can’t be sure that they are not automations. Descartes realizes that he cannot be sure that even other minds exist but he comes to a conclusion that he can know one thing and that is that he doubts.

Because he doubts he knows that he is a doubting thing. In order to doubt there must be something to do the doubting and that doubting thing is Descartes himself. Descartes conclusion is, “I think therefore I am.” Now that Descartes has established the one thing that he can be absolutely certain of he begins to construct other things that he believes he can know based on that single certainty.

The Ontological Argument

Descartes goal with the Meditations of First Philosophy was to make an argument for the existence of God. I feel that in order to do this justice I must give the argument a little background. Descartes was not the first to propose an ontological argument for the existence of God. His just happens to be the best one that has ever been proposed. There is an essential misunderstanding of the argument that nearly every modern reader of Descartes makes and that is a misunderstanding of what he means by the term “perfect” and “perfection.” Descartes does not mean “perfect” the way that we mean perfect today, as in the absence of flaws, but he means it in a context of a medieval definition.

When Descartes says perfection he means a “positive trait.” For instance, intelligence is a perfection while ignorance is not a perfection because it is merely the absence of intelligence. A perfect being would be a being that had all perfections, meaning all positive traits. Another concept that was widely believed during Descartes time was that in order for something of complexity to exist it must have come from something more complex. So if a human could have intelligence (a perfection) then he must have been created by something of even greater intelligence. (That would be God.) When most people look at Descartes argument they look at in from a modern perspective that has evolutionary biology as explanations for human complexity and a different definition of perfection so they often completely miss what the argument is saying.

After Descartes had established that he is a thinking thing he begins to try to extract other certainties from that concept. Descartes makes the next step that ideas are real and they come from him because he is a thinking thing. Certain ideas, he claims, are innate and those ideas include the ideas of mathematics. He needs no outside information to come to the conclusion that 2+2=4. This is true and he can be certain without any use of his senses. He goes on to say that ideas that are true by definition must be true. A triangle is a three sided figure. It is this by definition and therefore a triangle must exist because he can conceive of such an idea. A perfection, like Intelligence exists because he can conceive of such a thing. (so far so good.) God is by definition a being of all perfections. Existence is perfection because non-existence is merely the lack of existence therefore God must exist. (Here is where we have issues.)

Many philosophers tried to beat up on Descartes argument for a long time but it is a testament to how strong it was, based on the premises that people accepted at the time, that nobody ever really killed it completely until Immanuel Kant. Kant pointed out that existence is not a predicate. When you say that something exists because it must exist, this is true of anything that has any trait. A thinking thing must exist. An intelligent thing must exist. A strong thing must exist. Even a weak or ignorant or non-thinking thing must exist. Saying that something must exist because existence is necessary is redundant and proves nothing. Descartes definition of “perfection” was what was essentially flawed about the argument. Kant’s argument is considered the absolute death blow to Descartes Ontological Argument but even now we are still talking about it.


Descartes went on to accept that because God existed he could not necessarily be a deceiver and because God had created his mind, body and senses then the external world must exist. Satisfied that he had settled the whole matter, something he was completely wrong about, he dedicated a lot of time to defining the existence of the soul and how it worked. Descartes came to the conclusion that the mind was completely separate from the body. In philosophy of mind, what constitutes the “Mind Body Problem” is that the experience of consciousness and the physical processes of the brain and body seem so at odds with each other. Descartes came to the conclusion that this was because they interacted but were at the same time completely separate from each other.

In an effort to try and find some biological evidence for this, Descartes came to the conclusion that the mind and the body interacted in the pineal gland. His reasoning for this was that the gland was located at the base of the brain and while most human body parts came in twos, there was only one pineal gland. In reality, even Descartes was dissatisfied with this explanation and he struggled to come up with an answer to this problem for the rest of his life.


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    • profile image


      7 months ago

      This is so bad

    • profile image


      24 months ago

      great and awesome

    • profile image


      2 years ago

      nice thoughts

    • Amy Naylor profile image

      Amy Naylor 

      6 years ago from England

      Great hub. I've never actually read up on his argument for the existence of God so that proved a good overview for me. Thanks for sharing!

    • profile image


      6 years ago

      With ultimate team(UT) anaywy, more player position cards. I haven't played in awhile so perhaps they have added this in a recent update but I doubt it. To be able to change a LM to a CAM, a fullback to a L/RM etc because currently some of us can't truly have our UT when the game restricts us this way.


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