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Cogito, ergo sum

Cogito, ergo sum is a Latin phrase meaning “I think, therefore I am”. Used by the philosopher and mathematician René Descartes in the Discourse on the Method (1637), the formula has a variant in his work in 1641, in the Meditations on First Philosophy: ego sum, ego existo (“I am, I exist” ); then, he returns to that of 1637 again in 1644, in the Principles of Philosophy (ego cogito, ergo sum). For the philosopher, it expresses the first certainty which resists to a methodical doubt. Seeking to completely rebuild knowledge, Descartes wishes to find a solid foundation for it, absolutely certain. This research leads him to the conclusion that only his own existence, as a “thing that thinks”, is initially certain. It is this discovery that the “cogito” expresses. Regardless of the formulations, the cogito constitutes a major element of Cartesian thought. There is a certainty on the basis of which Descartes will attempt to rebuild all knowledge. It consists of an intuition which is not limited to a logical deduction.

In philosophical vocabulary, the expression is frequently shortened and substantiated. We simply speak of the cogito, to express the intuition acquired by the subject thanks to his consciousness of himself. The cogito is then taken as a discovery which is no longer always linked to Descartes himself. We thus speak of the Augustinian cogito, before Descartes, or of the Husserlian cogito, after him.

Cartesian cogito


The context of the 17th century is that of a questioning of the physical structure of the world. In 1633, Galileo was condemned by the Inquisition for having published the Dialogue Concerning the Two Chief World Systems, in which he took sides in favor of the heliocentric model of Copernicus; this is what we call today the Ptolemeo-Copernican controversy. In November 1633, Descartes, who himself also favored the heliocentric model, learned that Galileo had been condemned. He therefore cautiously gave up publishing the Treatise on the Light where he set out heliocentric theses (it would not appear until 1664), and preferred to publish a philosophical work, the famous Discourse on the Method (1637). Descartes knew Mersenne from 1637. He exchanged correspondence with him, within the framework of the networks of scientists of that time. In 1641, it was Mersenne that Descartes asked to collect the objections on the Meditations on First Philosophy.

Cogito ergo sum can therefore be understood as the attitude of a man who claims a form of thought contrary to that of the authorities of the Church, and proclaims his right to exist through thought.


The cogito is initially exposed in French by Descartes in the Discourse on the Method (1637), fourth part.

Descartes reiterates this reasoning, in Latin this time, in the Meditations on First Philosophy (1641):

Sed est deceptor nescio quis, summe potens, summe callidus, qui de industriâ me semper fallit. Haud dubie igitur ego etiam sum, si me fallit; & fallat quantum potest, nunquam tamen efficiet, ut nihil sim quamdiu me aliquid esse cogitabo. Adeo ut, omnibus satis superque pensitatis, denique statuendum sit hoc pronuntiatum, Ego sum, ego existo, quoties a me profertur, vel mente concipitur, necessario esse verum.

“But there is one je ne sais quoi, very powerful and very cunning, who uses all his industry to always deceive me. There is therefore no doubt that I am, if he deceives me; and that he deceives me as much as he wants, he could never make me be nothing, as long as I think I am something. So that after having thought about it well, and having carefully examined all things, finally it is necessary to conclude, and to hold as constant that this proposition: I am, I exist, is necessarily true, whenever I pronounce it, or that I conceive it in my mind.”

However, it was not until 1644, in the Principles of Philosophy (first part, article 7) that the word “cogito” (within the meaning of this article) appeared for the first time in the work of Descartes:

Ac proinde haec cognitio, ego cogito, ergo sum, est omnium prima & certissima, quae cuilibet ordine philosophanti occurrat.

“This thought, I think, therefore I exist, is the first and most certain which presents itself to the one who leads his thoughts in order.”

In the philosophy of Descartes

Descartes, who was involved in scientific research at the time, sought to leave to posterity a scientific method, based on methodical doubt, in order to lead to the search for truths.

Despite his practice of radical doubt, Descartes stands out from the skeptics. With these Greek thinkers, the epoche consists of a definitive suspension of judgment which aims to achieve ataraxia. This doubt should not be confused with Descartes’ methodical doubt, which is provisional and which is established with a view to the discovery of an unmistakable truth. The 17th century is a time of enrichment of thought. Many discoveries come to destroy the political, religious … unity of Europe. Man is therefore lost in an uncertain world where nothing is certain except error. But for Descartes, man cannot renounce “the assurance of judgment”. Skepticism is not a viable attitude. His methodical doubt is therefore a voluntary, reasoned and active doubt, which aims to achieve certainty, on which a safe and certain world can be reconstructed.

In the Discourse on the Method, it is a question of methodical doubt. Thinking requires the introduction of a method.

It is on the thinking subject that knowledge, morals and law are now based. To be a subject is to make sense of things and of oneself, it is to assert oneself as a free and responsible human being.

Descartes comes to want to prove also the existence of God, by the only fact that he thinks his existence. We read in fact important developments in the Meditations on First Philosophy in this direction (third Meditation: of God that he exists, fifth Meditation: of the essence of material things, and again of God, that he exists).


The cogito ergo sum developed in these three works therefore has considerable and timeless significance. Descartes affirms that he is a thinking being, and he asks the question of the existence of God, affirming that he exists.

Some then speak of a hyperbolic doubt: Descartes, pursuing his ideas already set out in the Rules for the direction of the mind, seeks a first principle, that is to say a foundation of all knowledge. It is about thinking: cogito, ergo sum (“I think, therefore I exist”).

In doing so, this principle becomes a certainty which replaces the conception of a first cause which was that of scholasticism, and which resulted from the reconciliation between Christianity and the philosophy of Aristotle, made by Thomas Aquinas in the Theological sum.

This principle is the basis of a new morality (the Principles of Philosophy).


A principle to be placed in its context

As we have seen, the context of the 17th century is that of a questioning of the physical structure of the world and the appearance of the heliocentric model.

It should be noted that Descartes himself contested the syllogistic character of the cogito, even if it maintains a deductive element in it. The “donc” of the French formula attests it. But as doubt puts reasoning in suspense, the deduction can be called into question here, at least when it is no longer intuitioned and when “reasons to doubt” flow. This difficulty, which Descartes points out and deals with, will occupy his readers as much as the specialists of Descartes in the years 1950-1970.

Posterity has often retained the formula: cogito ergo sum (“I think therefore I am”) contained in the Discourse on the Method (1637), detached from its context. The Discourse on the Method, easily readable because it was written in French, conveyed the concept of the cogito in the 18th century, then teaching in France popularized it. The successors of Descartes sometimes imagined that it was enough to think scientifically to arrive at certainty.

A forgotten metaphysics?

Posterity sometimes forgot the philosophical developments contained in the Meditations on First Philosophy. Descartes used the concept of the cogito, not only on the level of the scientific method (Discourse on the Method), but he gave it a metaphysical formulation: in the Meditations on First Philosophy, the main place is given to the thinking subject.

Many nineteenth-century philosophers claimed to be Descartes’ successors, even though they refused any value to metaphysics.

In fact, Descartes had a conception of metaphysics different from that of the scholastic school, which took Aristotle for reference, interpreting it in the tradition of Saint Thomas Aquinas.

Aristotle retained Ptolemy’s theory of geocentrism, hence the difference of opinion.

We read in the Principles of Philosophy:

“So all philosophy is like a tree, whose roots are metaphysics, the trunk is physics and the branches which come out of this trunk are all the other sciences which are reduced to three main ones, namely medicine, mechanics and morality, I mean the highest and most perfect morality, which, presupposing an entire knowledge of other sciences, is the last degree of wisdom. Now, as it is not from the roots, nor from the trunks of trees, that fruits are picked, but only from the ends of their branches, so the main utility of philosophy depends on those of its parts that cannot be learned. than the last ones.”

We see that, contrary to the teaching of the time, which was based on a reconciliation between the Bible and the philosophy of Aristotle (scholastic school), Descartes does not put metaphysics and morality on the same level. Indeed, on the basis of Aristotle’s work, philosophy was considered to include three major branches: logic, metaphysics, and ethics.


Kant has often referred to Descartes’ concept of the cogito, in particular in the Critique of Pure Reason. Kant shows the illusions that reason produces when it claims to know the noumena (God, freedom, the soul). Reason “thinks” by principle and when the application of principles takes place outside of experience, that is to say in the field of noumena (as opposed to phenomena), this risks being manifested by antinomies, paralogisms, etc. Kant thus criticizes the application that can be made of Descartes’ cogito in the service of a metaphysical pseudo-knowledge of the soul as substance, and the risk that certain applications lead to fallacious reasoning.

Auguste Comte

Auguste Comte does not explicitly take up this principle of Descartes. Like Descartes, Comte rejects first causes, but he goes further: there is no longer a first principle. He no longer uses the term metaphysics, he considers this branch of philosophy to be outdated, humanity having passed to a positive stage (law of the three states).

We find in Comte the idea of ​​subjectivity.

As an atheist, Auguste Comte ignores metaphysics. He therefore departs from Descartes on this point, even if he claims to be his successor.

Nietzsche, structuralists

Certain philosophical traditions severely criticize the cogito as the first principle, and this is, in general, to derive it itself from structures which precede it.

For example, Nietzsche or the structuralists denounce the cogito as being only a historically constituted illusion, and in no case as a universal invariant.


Edmund Husserl, after having worked on meditations, will attempt to found phenomenology. He is inspired by the cogito, more particularly by methodical doubt, to develop his épochè, the first movement of phenomenological reduction. Contrary to Descartes’ doubt, he does not deny the sensitive world, but leaves the question in suspense, moreover, the epochè is not a tool from which we separate ourselves once the first truth is posed. He rejects the immediate “reification” (“Quid enim sum? Res cogitans.” / “What am I then? A thinking thing”) that Descartes immediately induces in the Mediations.

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