I Think Therefore I Am: Descartes’ Cogito Ergo Sum Explained | Philosophy Break
17th-century philosopher Descartes’ exultant declaration — “I think, therefore I am” — is his defining philosophical statement. This article explores its meaning, significance, and how it altered the course of philosophy forever.
It’s a cool 1640 night in Leiden, Netherlands, and French philosopher René Descartes picks up his pen… “I am here quite alone,” he writes, “and at last I will devote myself sincerely and without reservation to the general demolition of my opinions.”
What better way to spend the night?
But Descartes was not without reason: in his work as a mathematician, he worried that if the foundations of knowledge were not completely solid, anything built upon them would inevitably collapse. He thus decided that if there was reason to doubt the truth of something — no matter how slim the doubt — then it should be discarded as false.
René Descartes, meaning business.
With this strict criteria for truth in mind, it’s not long before — as depicted with masterful drama in his Meditations on First Philosophy — Descartes struggles to feel convinced by the existence or reliability of, well, anything.
The fact we dream and hallucinate means, for Descartes, our senses aren’t always trustworthy. Indeed, have you ever woken from a dream and thought, “but my God, that seemed so real”? Have you ever hallucinated your socks off? Have you ever sworn to have witnessed something when someone else swears to have witnessed something else?
When our perception of the world fails us, it can be jarring. We take it for granted that our experience is authentic, so when it proves to be false it’s like a bucket of ice water to the face: “oh right,” you think, “my perception is not infallible — maybe I don’t always experience the real, true world.”
Are the dots above black or white? Optical illusions reveal just how easily our brains can be tricked or misled by everyday patterns.
But, according to Descartes’s strict criteria for truth outlined above, where does that leave us? If the authenticity of our experience can occasionally be doubted, then that is enough for Descartes to dismiss it as absolutely unreliable: that our senses can sometimes mislead us without our knowing suggests that they could mislead us all the time.
And, if we cannot trust information obtained from our senses, then how can we confirm the existence of an external world?
Maybe our brains are just in vats somewhere, hooked up to a load of computers, and all this ‘experience’ is mere simulation. Or maybe nothing physical exists at all and this is all just one big hallucination — everything is an illusion, a figment of the mental realm, or even the conjurings of an Evil Demon determined to mislead us about the true nature of reality…
Can we ever know for certain if the world we perceive is actually reality, rather than, say, a computer simulation?
And it’s not just our sensory capabilities that can be thrown into doubt: our ability to reason could also be hopelessly impaired. If we have reasoned incorrectly before, Descartes notes, how can we ever know for sure that we are reasoning correctly now?
Maybe 2 + 2 really equals 5, not 4, and it is again the workings of an Evil Demon that makes us think differently.
Poor old Descartes got himself into a right state over all this:
So serious are the doubts into which I have been thrown as a result of yesterday’s meditations that I can neither put them out of my mind nor see any way of resolving them. It feels as if I have fallen unexpectedly into a deep whirlpool which tumbles me around so that I can neither stand on the bottom nor swim up to the top.
By this point frantic with worry, Descartes seeks to repair some of the damage caused by his relentless doubting by groping around for something — anything — we can be absolutely certain of. And, after a while, he finds it.
Mục Lục
I think, therefore I am
A clearer translation of Descartes’ definitive statement might be, “I am thinking, therefore I exist.” Regardless, in his exultant declaration — cogito ergo sum! — Descartes assures himself of his own existence.
Phew. Mop that brow, eh René: at last, here is something we can be absolutely certain of. It is impossible to doubt the existence of your own thoughts, because in the act of doubting, you are thinking.
Life’s Big Questions: Your Concise Guide to Philosophy’s Most Important Wisdom
★★★★★ (50+ reviews for our courses)
Unlock philosophy’s best answers to life’s big questions with just one concise, 30-minute read per day.
Sign Up Now
Descartes believed his discovery of the Cogito to be hugely significant, for it withstands all the skepticism you can throw at it.
Indeed, even if you doubt the reliability of your senses, and even if you doubt the reliability of your reason (i.e. the two main sources for knowledge), the Cogito remains true. For, however wrong you are in your estimation of reality, you can never be wrong about the fact of your own existence, for in order to think you are wrong about something, there has to be a you that exists to be wrong.
So, Descartes establishes his base, his solid foundation for certain, indubitable knowledge: a thinking mind must exist.
From this point on in his Meditations on First Philosophy, Descartes attempts to rebuild all human knowledge and establish proofs for the existence of, among other things, God.
Alas, his work here is generally acknowledged to not quite make up for his initial demolition job. We may have certainty with the Cogito, but the possible unreliability of our senses and reason doesn’t leave much else.
Through absolutely bulldozing our confidence in the existence of anything but our thoughts, Descartes inadvertently created two separate realms: the mental and the physical. The mental we can be sure exists (however deceived or deluded that existence may be); the physical world needs to, somehow, be linked to it.
Believe it or not, philosophers have been trying to bridge this explanatory gap ever since.
Is there an answer to Descartes’ skepticism?
Descartes’ doubting leaves us with a rather alarming concern: that perception might not be reality, that our reasoning abilities are not necessarily reliable, and that our experience is not infallible and has no bearing on the existence of an external world. Of course, this state of affairs has prompted a vast literature on whether the skepticism expressed by Descartes is actually anything to worry about — including by the 17th-century philosophers John Locke and George Berkeley — which has in turn spawned commentaries on the limits to what we can know, as well as just how our existences are tied to that of the world around us.
There are a number of deep epistemological and metaphysical issues exposed by Descartes’ Meditations on First Philosophy, which is why it’s perceived to mark the beginning of modern philosophy in the Western tradition. Combine that with its highly accessible, dramatized style, and it’s no wonder that this short text is still pored over by undergraduate students to this day. It’s essential reading for anyone interested in philosophy.
Beyond reading Descartes’ Meditations on First Philosophy in full, to further explore the theme of what constitutes the ultimate nature of reality, touched on by Descartes’ pondering, check out our 5-day introductory philosophy course, Life’s Big Questions, in which you can unlock philosophy’s best answers to life’s big questions with just one thoughtful, 30-minute read per day. If you’re intrigued by philosophy, but don’t have time to wade through lots of books and secondary literature, this is the ideal place to start.
Life’s Big Questions: Your Concise Guide to Philosophy’s Most Important Wisdom
★★★★★ (50+ reviews for our courses)
Unlock philosophy’s best answers to life’s big questions with just one concise, 30-minute read per day.
Sign Up Now
