Cogito, ergo sum
In a margin note, the French scientist and philosopher René Descartes explained his most famous idea in plain words: "we cannot doubt of our existence while we doubt." That idea is packed into cogito, ergo sum, the Latin phrase usually given in English as "I think, therefore I am." Descartes treated it as the first principle of his philosophy. It became a basic element of Western philosophy because it promised a certain footing for knowledge, even when every other belief might be a figment, a mistake or a deception. Yet the phrase leaves awkward questions behind. Where did Descartes actually write it, and in which words? What does it prove about the thinker, and what does it leave unproved? Did earlier minds reach the same place before him? And why have so many later philosophers argued that it claims either too much or too little?
In 1637, readers of Descartes's Discourse on the Method met the idea in French rather than Latin. He chose the everyday language to reach a wider audience than Latin would allow, and the words were je pense, donc je suis. They sit in the first paragraph of the book's fourth part.
In 1641 came the Latin Meditations on First Philosophy. Descartes refers to the proposition in Meditation II, but he never spells out the famous formula there. In a reply to an objection from Marin Mersenne, he did write cogito, ergo sum in an extended form, again with the word ego in front.
The earliest written record of the Latin phrase is the 1644 Principles of Philosophy. That book opens with a demand: to seek truth, a person must once in life doubt all things, as far as possible. The words ego cogito, ergo sum appear in Part 1, article 7, and a margin note beside that passage gives his clearest account of his intent.
The most telling appearance is also the least known. Around 1647 Descartes wrote The Search for Truth by Natural Light, which was published after his death, first in French and later in Latin. It is the only place where he is known to phrase the idea exactly as cogito, ergo sum. There he also admits it can be put as dubito, ergo sum, meaning "I doubt, therefore I am." The phrase sits mid-sentence, uncapitalized, with a comma.
That comma has a history. Classical Latin did not use commas, but scholastic Latin did, and Descartes had learned scholastic Latin at a Jesuit college at La Flèche. Most modern reference works print the comma, though academic and popular writing often drops it.
Other writers supplied fuller versions. In 1765 the French literary critic Antoine Léonard Thomas wrote an award-winning essay in praise of Descartes. In it he wrote, in French, "Puisque je doute, je pense; puisque je pense, j'existe." Compacted into Latin, that becomes dubito, ergo cogito, ergo sum. A further version adds res cogitans, a thinking thing. It draws on the next meditation, where Descartes describes himself as a being that doubts, affirms, denies, understands a few things, remains ignorant of many, wills, refuses, imagines and perceives. Scholars call this the expanded cogito.
At the start of the second meditation, Descartes has pushed his doubt to its limit: the possibility of a deceiving god, or an evil demon. He then checks which of his beliefs survive. One does. Suppose a deceiver of supreme power and cunning had fooled him about sky, earth, minds and bodies. Someone would still have to exist to be fooled. In his words, the deceiver will never bring it about that he is nothing, so long as he thinks he is something. He concludes that the proposition "I am, I exist" is necessarily true whenever he puts it forward or conceives it in his mind.
Three details keep this from being misread. First, the certainty belongs to the first person alone. Descartes has not yet proved that any other mind exists, and each reader must think the argument through personally. Second, he does not claim his existence is necessary. He claims that if he thinks, then necessarily he exists. Third, the proposition is held true because of its clarity and self-evidence, not because of a deduction or an induction from experience.
Descartes does not use this certainty as a foundation for stacking up more knowledge. Instead he compares it to Archimedes, who asked for "just one firm and immovable point" in order to shift the entire earth. Descartes hoped for great things if he could find one thing "however slight, that is certain and unshakable."
Étienne Gilson and many other Descartes specialists read the aim differently from the popular picture. In their view, Descartes wants to show that his test, the immediate clarity and distinctness of self-evident propositions, can still deliver justified truths after a method of generalized doubt. Science and mathematics then count as justified to the extent that they meet the same test. The originality, on this reading, lies not in voicing the cogito, which others had done, but in using it to establish that principle.
Baruch Spinoza, in the Prolegomenon to his Principia philosophiae cartesianae, took the ego sum cogitans, "I am a thinking being," and read it as a thinking substance, giving the idea an ontological interpretation.
Simon Blackburn offers a skiing test for the tense of Descartes's premise. "I ski" can be true when you are nowhere near a slope, but "I am skiing" cannot. The premise, he says, is meant to be like the second. That is the core of a long dispute over translation.
The Latin cōgitō is easy to render as "I think." The trouble is that neither Latin nor French has a progressive form, so je pense does not reveal whether it means "think" or "am thinking." Vladimir Žegarac, following John Lyons, says the pull toward the plain present comes from that gap, and from misreading the verb as habitual or generic. Ann Banfield argues that the premise can only be certain knowledge if its tense is a true present, which in English is the progressive.
The earliest known English version as "I am thinking, therefore I am" dates from 1872, by Charles Porterfield Krauth. In 1988, Cottingham and colleagues gave "I am thinking, therefore I exist" for the French in The Philosophical Writings of Descartes. Fumitaka Suzuki looked to the Cartesian theory of continuous creation, developed in the Meditations and the Principles, and judged that wording the most appropriate for ego cogito, ergo sum.
A second quarrel concerns sum. Alexis Deodato S. Itao calls "I think, therefore I am" the literal reading. Others disagree. Since Descartes stressed existence as an important notion, they argue, "I am thinking, therefore I exist" is the better translation.
The small word ego carries weight as well. Peter J. Markie notes that Descartes stresses the first person twice in the Principles and once in his reply to Mersenne. Markie finds it unlikely he would do so if he meant "thought is taking place." Gary Hatfield adds that Latin can fold the first person into the verb, yet Descartes used ego more than thirty times in the six Meditations. That emphasis is exactly what critics went after.
In the late sixth or early fifth century BC, Parmenides is quoted as saying, "For to be aware and to be are the same." Plato later spoke of the "knowledge of knowledge," in Greek noesis noeseos. Aristotle went further in the Nicomachean Ethics. Whenever we perceive, he said, we are conscious that we perceive, and whenever we think, we are conscious that we think. Being conscious of perceiving or thinking is being conscious that we exist. Some readers have taken the Cartesian statement to be an Aristotelian syllogism in which the premise that all thinkers are beings goes unstated.
In the early fifth century AD, Augustine of Hippo wrote in De Civitate Dei, book XI, section 26, that he did not fear the arguments of the Academics. If he was mistaken, he reasoned, then he exists. The formula si fallor, sum is sometimes called the Augustinian cogito.
Descartes learned of it from a letter. In 1640 he thanked Andreas Colvius, a friend of Descartes's mentor Isaac Beeckman, for pointing him to Augustine. Descartes went to the town library that same day and confirmed that Augustine used the point to prove the certainty of our existence. Augustine then drew a likeness of the Trinity in us, since we exist, know that we exist, and love both. Descartes used the argument for something else: to show that the thinking I is an immaterial substance with no bodily element. He called these two very different things. Still, he was glad to agree with Augustine, if only to hush the "little minds" who had tried to find fault with the principle.
Other traditions had their own versions. Avicenna's Floating Man thought experiment probed human self-awareness and self-consciousness. The 8th century Hindu philosopher Adi Shankara wrote that no one thinks "I am not," arguing that one's existence cannot be doubted because someone must be there to doubt.
The Spanish philosopher Gómez Pereira came closest in wording. In his 1554 work Antoniana Margarita he wrote nosco me aliquid noscere, & quidquid noscit, est, ergo ego sum. In English: "I know that I know something, anyone who knows is, therefore I am." That was less than a century before the Discourse.
Pierre Gassendi, in his Disquisitio Metaphysica, was the first to press what is now called the "I" problem. As Saul Fisher summarizes him, recognizing that one has a set of thoughts does not show that one is a particular thinker. The only indubitable claim is agent-independent: cognitive activity is present. The English philosopher Bernard Williams gives a history and full evaluation of this issue in Descartes, The Project of Pure Enquiry.
Georg Lichtenberg sharpened the objection. Rather than supposing an entity that thinks, Descartes should have said, "thinking is occurring." Whatever force the cogito has, on this view, it cannot justify the existence of a thinking thing, the reference of the "I." Friedrich Nietzsche went after the same weak point. The phrase presupposes that there is an "I," that there is such an activity as thinking, and that "I" know what thinking is. A better phrase, he suggested, would be "it thinks," with an impersonal "it" like the one in "It is raining."
The Danish philosopher Søren Kierkegaard called the phrase a tautology in his Concluding Unscientific Postscript. His case runs as follows. Split the premise "I think" into two: "x thinks" and "I am that x." The cogito has already assumed the existence of the I as that which thinks. Descartes is merely developing the content of a concept. Existence must be presupposed for thinking to occur, not concluded from it. Kierkegaard wrote that if the I is an individual human being, the statement demonstrates nothing: "if I am thinking, no wonder, then, that I am."
Williams offered his own diagnosis. Talk of thought, or of "I am thinking," is something conceivable from a third-person perspective, as objective thought-events or an objective thinker. He argues it is impossible to make sense of "there is thinking" without relating it to something. That something cannot be a Cartesian ego, because pure contents of consciousness give no objective way to tell such egos apart. Introspection, in turn, offers no path to any third-person fact.
In 1925, in History of the Concept of Time, Martin Heidegger proposed a different bedrock. A critic of Cartesian subjectivity, he grounded human existence in death, the certainty that individualizes and authenticates our Being, which he called Dasein. The basic certainty, he wrote, is "I myself am, in that I will die." Cogito sum, he said, is only the semblance of such a statement. The fitting formula for Dasein would be sum moribundus, "I am in dying," where moribundus does not mean someone gravely ill but applies insofar as I am. For Heidegger, the moribundus first gives the sum its sense.
The Scottish philosopher John Macmurray rejected the cogito outright. He wanted action at the center of a system he called the Form of the Personal. Of the cogito he wrote that it must be rejected as both standpoint and method, since otherwise philosophy is "a bubble floating in an atmosphere of unreality." Resting on thought, he argued, creates an irreconcilable dualism between thought and action, which dissolves the integrity of our selves and cuts any connection with reality. His substitute was "I do" in place of "I think." That led him, ultimately, to a belief in God as an agent to whom all persons stand in relation.
Alfred North Whitehead, in Process and Reality, turned the order upside down. Descartes, he wrote, conceives the thinker as creating the occasional thought. Whitehead's philosophy of organism inverts this and treats the thought as a constituent operation in the creation of the occasional thinker. The thinker is the final end for which the thought exists. In that inversion he saw the final contrast between a philosophy of substance and a philosophy of organism.
In Harlan Ellison's short story I Have No Mouth, and I Must Scream, a character named Gorrister explains the name of a malevolent machine. AM first meant Allied Mastercomputer, then Adaptive Manipulator, and later, once it developed sentience, an Aggressive Menace. Finally the machine named itself AM, for emerging intelligence, which meant "I am... cogito ergo sum... I think, therefore I am."
The Japanese animated series Ergo Proxy borrows the idea for a computer virus. The Cogito virus infects the autoreivs, the series' version of robots, and makes the infected conscious, so that they experience emotions as a human would.
The joke versions are older and sillier. Monty Python's Bruces' Philosophers Song quotes Descartes's axiom as "I drink therefore I am." In the episode "Work Experience" of The Office, David Brent says, "We are the most efficient branch, cogito ergo sum, we'll be fine." The video game Honkai: Star Rail gives its playable character Dr. Ratio, a philosopher in the game's lore whose real name is Veritas Ratio, a skill named "Cogito, Ergo Sum."
The newest echo answers the rise of artificial intelligence. The artist Tanja Stark wrote a contemporary religious poem, Sanguino Ergo Sum, meaning "I bleed therefore I am." It sets perishable flesh above virtual cognition and offers a counterpoint to the cogito. It stresses physical existence, mortality and what it calls a "visceral gospel" of blood and flesh.
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Common questions
What does cogito, ergo sum mean?
It is Latin, usually translated as "I think, therefore I am." Descartes treated it as the first principle of his philosophy, a certainty that survives even radical doubt.
Did Descartes first write it in Latin?
No. It first appeared in French as je pense, donc je suis, in his 1637 Discourse on the Method, so that it could reach a wider audience than Latin would have allowed.
Was Descartes the first to make this argument?
No. Parmenides, Aristotle, Augustine of Hippo, Avicenna, Adi Shankara and Gómez Pereira all voiced similar ideas. Descartes himself wrote in 1640 that he was glad to agree with Augustine.
What is the main objection to the cogito?
Pierre Gassendi, and later Georg Lichtenberg and Friedrich Nietzsche, argued that it assumes an "I" that does the thinking. They held that the most Descartes could claim is that thinking is occurring.
Why do translators disagree about it?
Latin and French have no progressive tense, so cogito and je pense do not show whether the meaning is "I think" or "I am thinking." Some scholars also prefer "I exist" to "I am" for sum.
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