Home Non-Fiction Philosophy The Cogito Ergo Sum: An Introduction

The Cogito Ergo Sum: An Introduction


In his First Meditation, Descartes sought to eliminate all beliefs that he held in an effort to seek certain knowledge. With the Dreaming Argument, where he determined that sensory perception was fallible due to the possibility of all experiences being only illusions, Descartes proposed that empirical beliefs could not be certain knowledge (Descarte, 1984:13). A priori knowledge, or non-empirical knowledge, was previously held as viable by Descartes but the Evil Demon argument, where Descartes determined the possibility of a ‘great deceiver’ who could implant false knowledge into his mind, put even the most concrete beliefs into question (Descarte, 1984:15). With these arguments, Descartes had succeeded in his goal of demolishing all previously held beliefs as uncertainties, but now he needed to find what was unquestionably true. His solution to this was cogito ergo sum – ‘I think, therefore I am,’ or more precisely, ‘I am thinking, therefore I exist right now’ (Blackburn, 1999:27).With the Cogito, Descartes supposed that our very thinking proves our existence. By proving its necessary premise of ‘existing to think,’ using the premise to disprove the Evil Demon argument and determining the nature of our mind – the Cogito argument can be proven to give us certain knowledge of our existence.

I need to exist in order to think. Like any action, if I am the one to do it, my existence is required in order to do it (Blackburn, 1999:28). My thinking itself cannot be an illusion as the capacity to see illusions requires thinking in itself. There is no action without an actor is a good way of putting it. The actions of others, and even my own actions, are uncertain as they can merely be illusions brought up in the forementioned Dreaming Argument. My action of comprehending said actions, however, is an act of thinking. I may not always be thinking – but when I am, I exist – and as can be presumed by my existence during those times, I exist right now. Someone has to be doing the thinking, and as will be addressed shortly, I have exclusive ability to determine that it is me doing the thinking.

The Evil Demon, as mentioned before, cannot be the one deceiving me into thinking, as acknowledging his deception would be in itself: thinking. The goal of the Evil Demon was to deceive you of all things. As such, your existence should be mere deception by the Evil Demon. But as addressed earlier, we have determined that our existence is certain as we can think and acknowledge our existence. Blackburn (1999) was apt in saying that “the Demon cannot simultaneously” (Blackburn, 1999:28), make you believe that you exist when you do not. The very act of trying to deceive us also proves that we do exist. We have proven that our thinking verifies our existence and that our existence is not a deception by the demon. This refutes the premise of the Evil Demon Argument wherein everything could possibly be a deception of the demon (Descartes, 1984:17). Everything else could very well be a deception, but our existence cannot be.

We are the only ones who can perceive the inner workings of our own minds. Neurology seems to be able to sense the limited activity of our mind but, as we have established, that could merely be an illusion or deception by the Demon. Only our own existence is certain, so it is logical to conclude that only we have access to ourselves. Even if we are to presume that we are watching something else thinking within our own minds, we would still be thinking and our existence would still be certain. So it is sufficient to say that we are the ones thinking within our own minds. As such, it is we who are thinking and therefore, we exist.

We have established that we exist – but not what we (or more precisely, the ‘I’ of ‘we’) is. Descartes grappled with the same problem in his Second Meditation. When we think of ourselves, we picture our faces, our bodies, our interests, our social relations – but none of these things are certain (Blackburn, 1999:29). Our bodies, as physical entities, can just be illusions and so to can our friends and those around us. Then, what are we if not a body or a social entity? We have already determined that our existence is proven by our thinking but what if our existence is thought itself? An abstract proposition it may be but possible. Our entire limit to our engagement with this world is the way we think. We see, hear and perceive – all of which may be illusion – but the fact that we are partaking in the illusion requires our ability to think. Our body and image of ourselves may be illusion and Demonic deception, but our ability to dwell within this image, or to dwell on it, is an act of thinking itself. But, what is thinking? Perhaps, we are the thoughts themselves.

Descartes (1984) said, in his Second Meditation, that thought is inseperable from the soul  (Descartes, 1984:18). It is only a small step from being inseperable to being “it.” Descartes believed in a concept that has come to be called “mind-body dualism” – a concept that the mind is distinct from the body (Skirry, 2005). In this idea, he argued that the mind exists outside of the body and not as an extension of it. Descartes used this discinction as a premise for his Trademark Argument where he attempted to prove the existence of God (Skirry, 2005). Descartes views of God can be seen as a result of the Cogito but not necessary in understanding it, so I will not digress. What we can determine is that our existence is separate from what we would deem our “physical reality” – it is independent of the illusions of our dreams and the deceptions of the Demon.

Lichtenberg (1742-1799) is one such philosopher who criticised the Cogito. His famous statement was that “I think” should be “it thinks” – to the same degree that we would say, as he said it, “it thunders” (Blackburn, 1999:30). Lichtenberg argued that merely thinking is not a justification that we are the ones thinking. All we can prove is that thinking is going on itself – and that an entity known as ‘thinking’ exists.

Earlier, we argued that thinking, as an action, required something to do it. Lichtenberg seems to be arguing that that is not necessarily the case. Blackburn (1999) quite appropriately stated that you cannot have dents floating around without a surface – thoughts had to have an origin  (Blackburn, 1999:31). Thoughts originate from a thinker and do not occure independently of said thinker. As I am the only one with exclusive access to my own mind, and thus the thinker, it is suitable to say that Lichtenberg’s objection can be refuted. A thought must have a thinker, I am thinking that thought, therefore – I am the thinker, and therefore, I exist.

Descartes has found an example of certain knowledge. The “I” exists. For all people who think, to ourselves, we can be certain that we exist. But many would say that the Cogito was pointless. Yes, we exist – but in a “sea of doubt” (Blackburn, 1999:32). The existence of illusions and dreams calls our empirical knowledge into question, while the Evil Demon argument brings doubt to all our a priori and given truths. How can we exist when nothing else certainly does too? I, for one, don’t see the clarification of universal knowledge to be the real goal of the Cogito. Rather, the Cogito’s only goal was to create a life boat for us to stay afloat, so that we may find the vestiges of other truths that may exist. If we can be assured of our own existence, it gives us pause to seek out other truths. Additionally, living in a world of illusion may not be terribly unpleasant. A worthy example would be from the film ‘The Matrix,’ where Cypher comments on a steak, that it does not matter if the steak is actually an illusion – it tastes great to him  (The Matrix, 1999). Descartes, too, was not perturbed by this destruction of certainty that he had created. On the other hand, Descartes was confident of his ‘clear and distinct’ perception which he had formed with the Cogito (Blackburn, 1999:33). As a skilled mathemtician, he saw the world through reason. If he could find one truth, he could find more. It just so happens that that truth was his own existence – giving him the ability to trust in his own existence and, therefore, start building up from the ruins of the beliefs he had previously destroyed.

Descartes sought to destroy all his beliefs – leaving himself with the ability to seek out only certain knowledge. In doing so, he probably succeeded more in creating doubt than clarity. He left his previous views of the world scattered like rubble. With the creation of the Dream argument and the Evil Demon, he had destroyed all his beliefs. But he had no foundation to find certain knowledge when not even his own existence was certain. With the Cogito, Descartes gave himself the foundation he needed. We cannot prove the existence of our world, our actions or those around us, but we can have certain knowledge that we exist. Some may call this a lonely world where we can only be certain of our own selves – but Descartes’ goal was never to achieve a state of happiness. He wanted to determine truth and, with his meditations, he came as close as we can determine truth to be. Our world can still be an illusion, there may still be an Evil Demon but my presence in this deception is proof enough of my existence. I perceive, I think – therefore, I am.


Blackburn, S. 1999. Knowledge. In: Think. New York: Oxford. 15-48.

Descarte, R. 1984. First Meditation. In: The Philosophical Writings of Descartes. Cottingham: Cambridge University Press. 12-15.

Descartes, R. 1984. Second Meditation. In: Stoothoff & Murdoch, eds. The Philosophical Writings of Descartes. Cottingham: Cambridge University Press. 16-23.

Skirry, J. 2005. René Descartes: The Mind-Body Distinction. [Online]
Available at: http://www.iep.utm.edu/descmind/
[Accessed 26 March 2015].

The Matrix. 1999. [Film] Directed by The Wachowski Brothers. United States: Village Roadshow Pictures.

(This article was originally written as a first year Philosophy essay at the University of Cape Town)