Descartes – “I think, therefore I am”

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French philosopher Descartes is most famous for the infamous “Cogito ergo sum” and “Sum res cogito” argument. Translation: “I think, therefore I am” and “I am a thinking thing.”

Meaning that I must exists in so far that I have the ability to think or even doubt my own existence. And more specifically while I do so I exists.

It important to keep in mind that Descartes lived during a time where the Italian astronomer Galileo Galilei had been condemned in Rome for publishing the view that the Earth revolves around the Sun. Up until this point the world believed that the sun revolved around the earth. (This would later be referred to as the Copernican revolution)

Imagine believing something your entire life, something which has been taught in schools, and studied so meticulously with such great importance has now all of a sudden been proven as false. Would you be able to go on without doubting every other piece of knowledge you once took as true? I think It is safe to say that this fundamentally and drastically changed the way we think about our place in the universe.


So lets break down how Descartes initially got to this famous statement by analyzing the first chapter from his book “The Meditations”.


Throughout the first chapter, Descartes puts forward three crucial arguments to then which later build on.  He wants to understand our foundations of knowledge and ask how we come to know the things we know. His goal and aim in using these three arguments are to start fresh and find what he can only actually be certain of. Throughout this post, I will analyze and will delve deeper into these three skeptical arguments. 1. The senses argument 2. The dream argument and 3. The deceiving g-d argument. Along with analyzing all three arguments, I will then explain why when used systematically, Descartes is successful in achieving the aim of rendering all prior beliefs doubtful.

In the first meditation, Descartes contemplates how that many of the previous opinions which he held turned out to be false. Opinions which he held from childhood up until the time of this mediation. This means that knowledge up until this point has been built on a shaky foundation, containing certain cracks and thus leads Descartes to realize that he must build a new foundation for knowledge. One which is unshakable, built on only the things of which we can be sure of. In doing so, he must use the method of doubt to seek out the truth. This concept of doubt becomes central, where the crucial modern question is: Can I doubt my opinions and my former opinions as in all the things I was previously taught, or is there anything that I may know beyond doubt? And in using the method of doubt, this is a way to look for things beyond what we know, where the philosophical goal is in fact knowledge by doubting until you reach something which is beyond the scope of doubt.

Descartes comes to find out that he has previously accepted as fully true all that has come from the senses or through them. However, he discovers that either what we have learned from the senses or through them, has failed him in that some were false. As a result, his caution now dictates that he should never fully trust them once realized that they had deceived him. And so, this leads him to his very first argument in the meditations of whether or not he can truly trust his sense perception.

He begins this argument by stating that in the past his senses have misled him and so for this very reason he cannot fully trust his all of his sensory beliefs. For example, if the conditions are poor, such as dim lighting, objects are far in the distance, and so on, then he cannot trust those sense perceptions as he cannot always be certain that what he is seeing is in fact true.  For example, imagine a cup under water, we are unable to observe its dimensions or details accurately. It is also possible for us mishear people and mistake things in the distance for other things. The senses argument specifically tackles the empirical knowledge and school of thought. However, the argument is not very strong considering that even Descartes himself acknowledges that although the senses sometimes deceive us about things that are in poor perceptual conditions, there are still things which although learned from the sense possess no doubt. Such as, I know that I am sitting at my table writing this post. What reason would there be to doubt this?  We could compare ourselves to madmen who say they are made of candy for example, but they are just that, madmen. And Descartes notes that we should not follow their example. (This point is weak, considering he does not give us any real explanation and so could be seen as a soft spot for this argument)

Moving on to the second argument called “The Dream Argument.” In this argument, Descartes calls into questions all our sensory knowledge by stating that we can never actually be positively sure that when we are awake, we are not in fact in a dream. When we dream we feel as if everything around us is real and for this reason the doubt which this implies in enough for us to doubt our senses completely and fully. Descartes finds that when in his dreams he has all the same experiences as these madmen when they are awake. When he has been asleep, he has the same experiences of those familiar things we all know, such as me sitting at this table writing this post. When in fact I could be in a dream and be none the wiser. He has had very distinct things in his experiences of dreaming before, just as distinct or real as when he was awake. When he thinks clearly on the difference between dreaming and being awake, he finds that he can never fully distinguish between dreaming and being awake by any clear criteria. This is important because it means he cannot be sure if he even has a body or not. And these everyday types of perceptions, such as me sitting at the table writing this post cannot escape the dream argument as it passed the senses argument. The dream argument calls not only calls into doubt our sensory knowledge but all our a-posteriori knowledge. This argument specifically attacks the natural sciences which rely on experience, experimentation and observation. Descartes thinks that mathematical knowledge is not doubted in this argument because mathematics does not rely on any a-posteriori knowledge. Mathematics remains true even if everything else is false. Whether I am on mars on earth or in a dream mathematics remains valid. Regardless if there is no body or world. 4+4 will remain 8 here on earth or on mars. Since mathematics is about ideas, it is self-evident and does not rely on my sense experience or sensory perceptions, such as in the way the natural sciences do.


The final argument of the three skeptical arguments is the deceiving g-d or evil genius argument. The most radical of the three skeptical arguments. All the things that Descartes raised to escape the previous arguments cannot escape this argument. This argument gives him enough evidence to doubt the general principles that he believed as true from youth till the time of these meditations. He explains that there is a very slight possibility that a deceiving g-d or demon exists which plays with my mind, to the point that I cannot even trust my mathematical calculations or a-priori knowledge. (I know what you’re thinking, a deceiving g-d really? but keep in mind that Descartes is using the method of doubt. Meaning that anything which has even a .01% chance of falsehood is enough to doubt it entirely so stay with me on this one) So, this  deceiving g-d may mess with my psychological states and cognitive capabilities which may lead me to believe that these mathematical calculations are true when they may actually be false. That perhaps my mental faculty is built in such a way that it prevents me from recognizing truths as true and prevents me form having the capability from seeing falsehoods as false. Meaning That this evil genius or deceiving g-d created my mind in in such a way that it should be faulty.  This argument is crucial since it shows how a-priori knowledge such as mathematics which only requires reason without experience can be called into doubt, something the dream argument could not do. Here we see a clear distinction between the natural sciences where the evidence for validity rely on the physical where they experiment and observe, and mathematics, which is all about ideas. Mathematics remains true regardless if everything else is false. Whether I am dreaming, or in bad perceptual conditions, it will remain true. And so, does not depend on my sense perception as in the way that the dreaming argument does. Ultimately the deceiving g-d arguments leaves us with the ability to even doubt our reason. And in using the deceiving g-d argument after the dream argument, Descartes successfully tears apart both empirical and rational schools of knowledge where both our a-posteriori and a-priori knowledge has been cast into doubt. And according to this method, the slight possibility of doubt is enough to rule out that knowledge as a whole.

Ultimately the aim in using these arguments was successful in the sense that by using them from weakest to strongest Descartes was able to build his case rationally by using only his reason. It is important to remember that what he is in fact after is the truth. He is looking for something unshakeable, something that cannot be called into doubt in even the slightest as to later use and be able to build on what we can know for sure. As or the validity and success of the three skeptical arguments he only needs something sufficient, not certain, to break down the false beliefs that he once held. Since once the foundation is weakened the rest of his beliefs collapses.

He ruled out both the empirical school of thought and rational school of thought by method of skepticism. And in doing so, is left with a clean slate to build on, one that cannot be broken down in the attainment of truth and knowledge.

So what remains with Descartes after going through these arguments?

Drummmmm roll please………


Let just say we are in our worst case scenario of an evil genius or deceiving g-d and that everything I think and experience is false. Even when I am convinced of things that are not true I must exists in order for those things to not be true. The fact I am even doubting means that I am having psychological states to doubt, and so, I must exists in order to do so.

This argument Is  intended at a simple intuition of the mind, but remember that this insight is something one can only make about oneself not anyone else.


So what do I know about myself? I need to peel away all the things I thought I knew. Such as, I have a body or any physical things, nutrition, eating or drinking etc, because I don’t know if it’s real or that my accurate sense perceptions are even real. So then what am I left with that I am certain of? That I am a thing that thinks.

He continues on this point that I know that I exists as a thinking thing and that I exist when I think and elaborates; Thinking is not just one thing but a bunch of different things that are different from one another which can possibly be: doubting, understanding, affirming, denying, willing, unwilling. imagining, and having sensory perceptions. 

Here Descartes has now created the first layer to a new edifice of knowledge.


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