Rene Descartes’ Cogito and Two Criticisms

French philosopher Rene Descartes (1596-1650) attempted to put knowledge on a firm, indubitable foundation by engaging in a methodology of doubt that rejected as false anything that is conceivably uncertain.

Descartes reasoned to an extreme form of skepticism that made all beliefs he took for granted, such as that there is a physical world of objects, other minds, that he himself has a body, etc., open to doubt. He reasoned, moreover, that although he could doubt these beliefs he could not apply this doubt to his own existence. Descartes concluded that he must himself exist in order to doubt that he exists. This, Descartes argues, is inescapable and he explains it as follows,

“I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I too do not exist? No: if I convinced myself of something then I certainly existed. But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case, I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind” (1).

So, writes Descartes, “I must finally conclude that the proposition, ‘I am,’ ‘I exist,’ is necessarily true whenever it is put forward by me or conceived in my mind”. On this view, the very fact that I am thinking suggests that there must be something engaged in that activity, namely an “I.” Descartes presented this indubitable piece of knowledge in his famous Cogito, ergo sum: “I think, therefore I am.”

Descartes doesn’t stop there as he uses his principle to prove the existence of other things. He jumps from his Cogito to the trustworthiness of intellectual perception and then to the existence of a perfect being in God, which he believed to be an innate idea.

Criticism of the Cogito

Although Descartes’ Cogito seems commonsensical not all philosophers have agreed that it is sound.

A common objection is that Descartes claimed too much when he introduced the “I” (a substantial self) into the equation. Bertrand Russell objected that the word ‘I’ is “illegitimate” and that Descartes should rather have stated his premiss in the form “there are thoughts”. Such would, according to Russell, not presuppose the existence of a unified consciousness having the thoughts before setting out to prove that such a unified consciousness exists. For example, there is a major difference between the statements “There is pain” and “I am in pain.” Equally, there is a significant difference between the statements “There are thoughts” and “I am thinking”. But Descartes, argues Russell, is entitled only to the former and is not warranted to jump from “there are thoughts” to “I think, therefore I am.” Such a criticism suggests that the only indubitable knowledge is that thoughts exist, while the existence of an “ego” or a self is dubitable.

Some have believed that to better understand the flow of logic, the Cogito should be formulated into a syllogism. The following has been proposed:

P1: I think
P2: Whatever has the property of thinking, exists
P3: I exist.

But it is here that a flaw in the argument becomes evident in that it is circular. This fallacy occurs when the premises to argument presume, openly or covertly, the conclusion that is to be demonstrated. How does the Cogito commit this? It does so by assuming that I already exist (P1) in order to conclude in P3 that I exist. Descartes assumes what he attempts to prove, which is that there exists a particular person endowed with the capacity for thought.


  1. Newman, Lex. 1997. Descartes’ Epistemology. Available.

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