Cogito, Ergo Sum, or “I think, therefore I am.” This philosophical statement has made Rene Descartes one of the most famous philosophers of all time and the “father of modern philosophy.” Descartes was one of the first notable figures to completely abandon Scholastic Aristotelianism, a school of thought that had dominated European university teaching for centuries. He was also responsible for developing a modern theory of mind-body dualism and promoting a new method of science that was grounded in experiments and scientific observations. However, Descartes is best known among philosophers for his system of methodical doubt, also known as Cartesian doubt. Descartes exercised radical doubt, questioning dogma and philosophical claims to truth and even the reliability of our individual senses and cognitive faculties.
The Origins of “I Think, Therefore I Am: René Descartes’ Life
René Descartes (1596-1650) was a French philosopher, mathematician, and scientist. Born and raised in France, he traveled extensively around Europe and spent most of his working life in the Dutch Republic.
Descartes was well-known during his lifetime for his commitment to open dialogue with other philosophers. He invited other thinkers to publish responses to his work. He then collected them and responded to their reflections in turn. After a successful academic career, Descartes spent the last year of his life in Sweden, tutoring Queen Christina (although apparently the two didn’t get on). Descartes died of pneumonia in February 1650, having earned fame as one of Europe’s most famous philosophers.
Descartes’ Philosophical Writings: Meditations on First Philosophy
In 1641, Descartes published his Meditations on First Philosophy. Written in Latin, it contains critical responses from thinkers including Thomas Hobbes and Pierre Gassendi (as well as Descartes’ replies to them).
The Meditations are important because they set out René Descartes’ epistemology. Descartes seeks a specific kind of knowledge, which some academics have referred to as “perfect knowledge” or “irrefutable knowledge.” Descartes describes this in the Meditations thus: “[As] soon as we think that we correctly perceive something, we are spontaneously convinced that it is true. Now, if this conviction is so firm that it is impossible for us ever to have any reason for doubting what we are convinced of, then there are no further questions for us to ask: we have everything that we could reasonably want” (Cottingham et al, 1984).
Descartes believes that perfect knowledge requires us never to have any reason whatsoever to doubt it. In other words, the absence of doubt is what makes perfect knowledge. This is a very high standard to apply to any given statement of supposed fact. Still, in the Meditations, Descartes persists in trying to establish various items of knowledge that we can rely on with absolute certainty.
Cogito Ergo Sum, or “I Think, Therefore I am”, in the Meditations
Descartes spends much of the first part of the Meditations establishing how and why everything we assume to be true can be doubted. He establishes that all his thoughts might well be mistaken. Fortunately, help is at hand. It comes in his famous formulation, “cogito ergo sum,” often referred to simply as his “Cogito.”
At the start of the Second Meditation, Descartes wrote the following:
“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.”
(Cottingham et al, 1984)
Let’s unpack this passage a little bit. Descartes first asks whether he can even be sure that he exists. But he then realizes this is not in doubt because if he can convince himself of something, then he must exist.
He then argues that even if an all-powerful, evil demon tried to deceive Descartes into thinking that he exists when he actually does not, Descartes must exist in order for the demon to try and deceive him in the first place. Therefore, whenever he thinks, he exists.
Although it’s not spelled out word for word here, Descartes later clarified this position through his famous statement “cogito ergo sum,” i.e. the philosophical saying “I think, therefore I am,” Even though Descartes has previously argued that the existence of his physical body can be doubted, the existence of his thinking cannot. Philosopher Barry Stroud helped to explain this by noting: “A thinker obviously could never be wrong in thinking ‘I think’” and “no one who thinks could think falsely that he exists” (Stroud, 2008).
Of course, there have been plenty of criticisms of Descartes’ Cogito. But this is the basic meaning attached to his most famous and thought-provoking dictum.
Further Points of Discussion Concerning “I Think, Therefore I Am”
What’s most interesting about the Cogito is how personal it is to the interlocutor who speaks it aloud. The phrase has to be in the first-person and falls apart if we change it to the third-person e.g. “Descartes thinks, therefore he is.” We cannot say with any unshakeable certainty that Descartes is thinking. I can only assert my own thinking and my own existence beyond any reasonable doubt.
“Cogito ergo sum” also ceases to function if we change the tense of the phrase. I cannot say: “I existed last weekend, because I was thinking then.” What if I’m misremembering events from last weekend? Doubt instantly floods into this phrase. Cogito is grounded in the idea that we cannot try and think away what we are thinking right now in the present.
How to Define the “I” or the Self in the Cogito Ergo Sum
Many philosophers have discussed what Descartes is referring to when he says “I” in this sentence. Particularly since Descartes himself states: “But I do not yet have a sufficient understanding of what this ‘I’ is, that now necessarily exists” (Cottingham et al, 1984). In other words, Descartes has established that he exists but does not seem to know what he is. He cannot complete the statement “ego sum,” which simply means “I am.”
Pierre Gassendi was one of the first thinkers to point out that we can’t be sure what the “I” means. Therefore, the only thing that Descartes can reliably say is that “thoughts are happening” or “thinking is occurring” because we don’t know from this sentence that an entity is thinking. There is no evidence from “cogito ergo sum” for the existence of a rational thinking thing.
Descartes and the Influence of “I Think, Therefore I Am” on Later Philosophy
Descartes would probably have been surprised by the influence of his Cogito on later thought. However, the Meditations involve a radical shift in the history of philosophy. Rather than debating “what is true,” Descartes asked, “of what can I be certain?”. In doing so, he removed the authority of various bodies (particularly the Church) to claim truth and instead showed how certainty relies on our individual judgments.
In most modern societies, God is not accepted as the ultimate guarantor of truth. Instead, human beings are their own guarantors, equipped with reason and the ability to doubt. Thanks to this shift, Descartes is often credited with inspiring the Enlightenment to look outside religious doctrine for a proper understanding of the world.
Descartes’ Other Philosophical Ideas
While “I think, therefore I am,” has become Descartes’ most famous philosophical idea, he had many highly influential propositions.
Descartes established Cartesian dualism, which postulates that humans have two foundations: the mind and the body. The mind can exist outside the body, in contrast to the material body. The mind is non-physical and non-spatial, an immaterial substance that occupies no physical space.
He suggested that we can have no true knowledge of the physical world but only mental representations of things in the external world. He argued that evidence for the physical world required proof beyond the physical senses.
Descartes then provides proof of the existence of a benevolent God who provided him with a working mind and sensory system to seek truth and that this god is not trying to trick him. This allows Descartes to establish the possibility of acquiring knowledge about the world on the basis of deduction and perception. Consequently, he argues that reason is the only reliable method for attaining knowledge.
Bibliography
Cottingham, J., Stoothoff, R. and Murdoch, D., 1984. The Philosophical Writings of Descartes. 1st ed. Cambridge: Cambridge University Press.
Stroud, Barry, 2008. “Our Debt to Descartes,” in A Companion to Descartes, ed. Janet Broughton and John Carriero, Oxford: Blackwell.
Originally published: October 28, 2022. Last update: February 14, 2025, by Jessica Suess.
