Archive | 30 March 2023

The Cartesian Method, Pillar of Modern Philosophy

La version française de l’article est disponible ici.

Note: Reading René Descartes’ Discourse on the Method inspired me to write this article in which I present my thoughts on the content of the treatise. I’ve produced this text study without prior knowledge of his other writings and existing analyses on his work, except the one contained in the Flammarion edition of the Discourse (ISBN : 978-2-0813-9071-3).


René Descartes (1596-1650) is one of the philosophers who had the most influence on science and our current relationship to the physical world. Many still today, especially amongst scientists, define themselves as Cartesian, a qualifier that has become synonymous with logical and methodical.

The Discourse on the Method is his first published text and was released anonymously in Leiden (Holland) in 1637. Its publication took place during a period of intellectual upheaval regarding man’s place in the universe, weakening the Church and its authoritarian dogma. In fact, 1616 was the year of the first condemnation of Galileo for having supported heliocentrism and the movement of the Earth. It was not until 1620 that this hypothesis of the movement of the Earth was allowed.

The aim of the Discourse is to offer a method that allows a universal science, explaining the so-called abstract sciences at the time, such as medicine, with as much rigour as the “hard” sciences, first and foremost mathematics.

By presenting his method, Descartes claims to demonstrate the existence of God and the soul, reveals certain aspects of his morality, and exposes a critical look at the Church’s authoritarian dogma and the intellectual elite in place.

Title page of the first edition of the Discourse on the Method (Leiden, Holland, 1637)

The method

Descartes describes his method concisely and defines it in four rules in the 2nd part of the book: i) carefully avoid “prejudice” (i.e. prevention) and premature conclusions, ii) divide each of the difficulties to be examined into as many parts as necessary to better solve them, iii) order one’s thoughts starting with the simplest objects, iv) and finally omit nothing.

Critical mind

We note the importance of critical thinking in his method, notably in avoiding prejudice and premature conclusions, thus encouraging the fight against all types of biases. Descartes even prevents himself from establishing deductions from his own rules as he’s concerned that some people will use his findings as dogma rather than practising their own critical thinking. He goes so far as to forbid his readers to imitate him in order to ensure that they first take a critical look at his method.

Similarly, he never trusts his first thoughts. This technique of thinking against oneself and of questioning his a priori has led him to rarely be faced with an argument he had not foreseen. Descartes warns, however, that introspection and the exercise of critical thinking against one’s own beliefs is not without danger, advising impatient people, who are devoid of modesty about their own abilities and hasty in their judgments, against discarding all opinions that they have integrated until now at once, at the risk of remaining “lost all their lives”.

Whilst advocating a critical spirit, Descartes encourages human curiosity and reading, activities he holds in high esteem, declaring that “reading good books is like engaging in conversation with the most cultivated minds of past centuries”. Nevertheless, he encourages suspicion and to examine the content of the books rather than to indiscriminately drink the knowledge they contain, “in order to learn their true value and avoid being deceived by them”. He also warns against overinterpreting a text and finding solutions to difficulties posed by it, which the author may not even have considered. This cognitive bias can cause someone to regress and even become less knowledgeable than by refraining from studying at all. He also urges curious people to be as interested in the works and practices of the past as of the current ones, lest be at the risk of being disconnected from the present.

The good sense

For Descartes, a methodical mind must also be equipped with a good intuition to allow the intellect to understand true things, because according to him “things we conceive of very clearly and distinctly are all true.” He calls this capacity “the good sense” and devotes the first sentence of his Discourse to it: “Good sense is the most evenly distributed thing in the world; for everyone believes himself to be so well provided with it that even those who are the hardest to please in every other way do not usually want more of it than they already have”.

Beyond the ironic nature of this introduction, he explains in his treatise the importance of good sense which gives the mind the feeling of ownership and being at the origin of the knowledge that mirrors it. This virtuous psychological cycle comes from the pleasure one has in learning by oneself, a mechanism particularly in use when “proving effects from causes”. He therefore praises the intellectual construction in stages rather than starting from a ready-made truth, because the idea is then “much easier to conceive of” for the mind. Indeed, “we cannot so well grasp something and make it our own when we learn it from someone else as when we discover it ourselves”.

Rigour in sciences

Descartes refers to William Harvey (1578-1657), an English physician who dedicated his work to the heart and blood circulation. He praises Harvey’s work that establishes a more rigorous basis for medicine, which was considered at the time as an abstract science. The physical explanation of complex and abstract phenomena appealed to Descartes who also described in his Discourse the concept of “animal spirits”, particles present in the blood and in the nerves that were considered to be responsible for the movement of the body and to be the link between the senses and the mind. He seeks to apply as much rigour to all reflections on the world and aims to make philosophy a science.

Balance between theory and practice

He remarks, “in respect of observations and experiments, that the further we progress in knowledge the more necessary they become”. Effectively, he encourages moving forward by elementary steps, reasoning with chains of causes and consequences, and then demonstrating them through experience, rather than developing a pure intellectual construction. This is a compromise between theory and practice, both essential because, according to him, our reason is corrupted by society, and we cannot completely trust our perception of reality since we can be betrayed by our own senses. Verifying the theory by experience also makes it possible to protect against false principles and beliefs, which is consistent with the idea that he defends in his work of taking intellectual distance from dogmas and laws.

Statue of René Descartes in the city of Descartes, France (Photo: Jean-Charles Guillo, 2008)

His moral code

His moral code, which he calls “provisional”, is described in the 3rd part of the book and consists of a few maxims.

First, obey the laws and customs of the country in which one resides, including the respective religion. He also speaks of “regulating his conduct by that of the people among whom he was to live”. One can notice here a flagrant contradiction with his precept to depart from any influence of society during his reflections. This shows his eminently political character in his relationship to the world, especially in his works, where he must find compromises between diplomacy in society and intellectual integrity.

Second, observe what people do rather than what they say, because true beliefs are seldom expressed consciously. Indeed, he notices that the fact of believing and knowing that one believes are two mechanisms of thought which are mutually exclusive most of the time. This study of mankind also allows one to draw inspiration in order to choose the best path for their own life.

Third, among many “equally widely received” opinions, one should always skew toward the more moderate, because extremes have a propensity to be bad, especially when they take away our freedom.

The fourth maxim is to be as firm and resolute as possible in one’s actions. He hates sceptics and considers them irresolute people who doubt for the sake of doubting. He allows himself to estimate the veracity of opinions according to their probability, but is absolute in his assertiveness when acting: “You must be resolute in your actions even though you remain irresolute in your judgments” (letter to Reneri for Pollot, April or May 1638, AT II, ​​p. 34-36).

And fifth, to question himself when reality contradicts his thoughts, because it is easier to “change his desires rather than to change the order of the world”.

These maxims, as well as the truths related to his faith, constitute the only precepts he cannot question, unlike everything else. It is surprising to notice once again the dichotomy between the prejudice that he seeks to avoid in his logic, and his faith that he presents as the basis of his moral code. Indeed, faith is a truth which by definition is not intended to be questioned. His speech lacks introspection about it, effectively displaying none. We should perhaps take Descartes’ faith here as an assertiveness around a question on which he is not completely fixed, thus respecting his fourth maxim. And if faith is here linked to religion, it is the dogma par excellence! It seems to me that he was able to voluntarily display his faith to protect himself from possible condemnation from the Church when his book was published. This would have been a pledge of allegiance in order to be able to disseminate the seeds of reason to the greatest number, in particular thanks to the use of French rather than Latin, thus avoiding detection. Regarding his personal conviction, it seems, however, that Descartes was a believer since he regularly prayed to God (Adrien Baillet, The Life of Monsieur Des-Cartes, II, I, t.1, p. 81-86).

René Descartes in Amsterdam. Hand-colored woodcut (Photo: North Wind Picture Archives)

Metaphysical aspect

The existence of the soul and God

For Descartes, the perception of the world is achieved through our senses and therefore, as these can betray us, what we call reality can always be debated. It is true that dreams seem so real to us when we are immersed in them. Despite the temptation to think that everything is false, there remains at the same time a truth, which is that we are thinking. From there comes the famous saying “I think, therefore I am” (“ego cogito, ego sum, ego existo”), translating the author’s hypothesis that a being is a substance distinct from the body whose whole essence is to think: he identifies it as our soul. Indeed, we can always doubt the material things, but not our being, therefore our being is not material.

It then follows that our mind, being able to envisage a being more perfect than ourselves, must have been inspired by a superior being, because this idea, “for it was manifestly impossible that we should hold this from nothing”. He is obviously talking here about God, to whom we owe everything we know and on whom we depend. He goes on to argue that our senses would be of no help to us in interpreting the world if we did not have an intellect. Therefore, the fact of “having a body, or there being stars and an earth and suchlike, is in fact less certain” than the existence of God, “a perfect and infinite being”. He defends that the very principle of perfection in the human mind comes from God, written in Descartes’ style as follows: “if we did not know that everything that is real and true in us comes from a perfect and infinite being, then, no matter how clear and distinct our ideas were, we would have no reason to be assured that they possess the perfection of being true”.

This display of proof is astonishing in its conciseness. Indeed, he takes at most five pages to prove the existence of the soul and of God, without even considering any counter-argument. Such an important subject would surely have, from a perfectly honest philosopher, deserved a more elaborated development. As a comparison, he takes about 11 pages to present his point of view on common sense and critical thinking. It is difficult here to judge the honesty of Descartes on such a subject, given the political context and the ideology imposed by the Church at that time.

His view on animals

Soul, thought and reason are the things that separate us from animals. In this sense, Descartes disagrees with Montaigne (letter to Newcastle of the 23rd November 1646, AT IV, p. 573-575). He also refutes the idea shared by “ancient thinkers, that animals speak, although we do not understand their language”. For him, the movements of animals are those “of their fear, their hope or their joy, so that they can do them without any thought”.

To support this reasoning, Descartes imagines machines resembling humans, like complex automatons, which at first glance would not be different from us. However, it would always be possible for him to distinguish humans from machines, and this for two reasons: first “they would never be able to use words or other signs by composing them”, then “it is practically impossible for there to be enough different organs in a machine to cause it to act in all of life’s occurrences in the same way that our reason causes us to act”. One can wonder what Descartes would have to say about the advent of artificial intelligence and its potential future transversality of application with the already announced arrival of 3rd generation AI for 2030 (The War of Intelligences, Dr. Laurent Alexandre).

René Descartes in his workshop (Photo: ©Getty – ©Historical Picture Archive)

A stoicist view

Descartes advocates the use of reason, which he defines as discerning the true from the false and the requirement of certainty. Here, the rationalisation of human knowledge is performed by setting aside emotivity, the imagination turned towards the future and the memory which is the reminiscence of the past. In this sense, the philosophy of Descartes finds links with stoicism, particularly in distancing the imagination by anchoring himself fundamentally in the present, whilst keeping control of reason in the face of the tumult of emotions (Meditations, Marcus Aurelius).

The occasional use of the word pleasure in the Discourse (on three occasions) is noticeable, whilst it is considered an irrational movement of the soul according to Stoic doctrine. Good affection corresponding to pleasure would be the joy here.

A more logical than dialectical truth

For Descartes, it is preferable for a reasoning, a work, a philosophy, to be composed by the hand of a single person rather than the product of several people’s contribution. Man can recognise a tendency towards the purity of an idea by preserving it from external interference. This approach consists of trying to reach an absolute truth, which is a more logical than dialectical approach. Indeed, he speaks of the “knowledge of the truth” as a prerequisite for judging well (letter to Élisabeth of the 15th September 1645, AT IV, p. 291-293), not missing the use of the definite article here. Likewise, he evokes the idea of ​​perfection inspired by a superior being, confirming that he believes in an absolute, which therefore applies logically to the notion of truth.

He rejects in the same way the scholastic method of disputatio (in practice in the Middle Ages), which consisted in testing opinions through controversy, because one is then more concentrated on demonstrating the likelihood of an idea rather than weighing the reasons. Indeed, the best lawyers do not necessarily make the best judges.

Galileo before the Holy Office (painting by Joseph-Nicolas Robert-Fleury, 1847)

Political aspect

Ideological context

In 1633, Descartes abandoned the publication of The World after Galileo’s second condemnation that same year. The Church then exercised intellectual coercion and imposed its vision of the world in an authoritarian manner. In fact, all copies of Galileo’s Dialogue Concerning the Two Chief World Systems were burned in Rome. Descartes rejects this condemnation, considering that this theory of physics is detrimental neither to religion nor to the state. His intellectual proximity to Galileo is confirmed in his private correspondence when he says of the movement of the Earth: “I confess that, if it is false, all the foundations of my philosophy are also false, for it is evidently demonstrated by them” (letter from Descartes to Mesrenne in November 1633). Descartes chooses integrity and refuses to amend his work for the sake of having it published: “I liked it better to delete it than to make it appear crippled” (letter to Mesrenne in November 1633).


The historical context forces Descartes to be cautious, and the Discourse is therefore published anonymously for the first time in 1637 in Holland. At first, he did not want his work to be published during his lifetime as he foresaw the opposition and controversy that it would give rise to. He was aware that this would have taken away precious time from him, which he intended to use to educate himself. Plus, he adds that he hates glory, inasmuch as he considers it the opposite of rest.

Thus, Descartes chooses to reveal only the minimum to explain his method and refuses to make deductions from it or to illustrate it with examples that would lead to controversy: “I thought it was easy for me to choose a few topics which, without being subject to much controversy, nor obliging me to declare more of my principles than I wish…” (letter to Mesrenne in April 1634). He wants to avoid falling out with the learned, and more generally the people who are seen to hold the truth, such as those who are part of the Church. There is a paradox here with the fourth maxim of his moral code consisting in having total assertiveness when the moment comes to act, and that the conviction must be absolute, even though one cannot be completely sure of a hypothesis at the moment of reflection. Indeed, the behaviour he seeks to avoid among the learned is the very one he advocates. We can also note that encouraging absolutism at the time of action is a characteristic feature of the political world, in opposition to the philosophical world which can allow itself a relativism, or question its certainties as Nietzsche will say later (The Gay Science).

He takes the precaution of showing his humility towards God and religion on several occasions, as a pledge of moral probity towards the Church. In these passages, he generally does not fail to add a touch of irony, which makes their reading particularly rich: “I did not wish to infer from all this that our world was created in the way I suggested; for it is much more plausible that from the beginning God made it as it was to be”.

Criticism of society

Descartes takes a critical look at society in many ways. He claims that its influence perverts our judgement, and that if we had all our reason from birth, our judgements could not be purer. The intellectual paths that society carves for us, so to speak the dogmas, are so taken that it is now easier to practise them than to trace one’s own path in a straight line to one’s destination.

This distrust of dogma converges with his distrust of the established order. He does not take economic wealth as a guarantee of knowledge and even affirms in his private correspondence that “those who are born great and happy [,] have the most opportunities to make mistakes” (letter to Reneri for Pollot, April or May 1638, AT II, ​​p. 36-37).

The detrimental influence of society also leads us to pay more attention to what will be seen by many rather than what we do only for ourselves. It is a tendency of the human being that Blaise Pascal also underlines at the same time in The Thoughts.

Optimism towards the people

Descartes chose to write the Discourse in French, and not in Latin as was customary, to address the people directly, far from dogma and bypassing the scholars of the time: “if I write in French, which is the language of my country, rather than Latin, which is that of my teachers, it is because I hope that those who use only their unalloyed natural reason will be better judges of my opinions than those who swear only by the books of the ancients”. Here, he admonishes an intellectual rigidity among the learned and instead appeals to common sense against authority. Sharing knowledge is not everything, one also has to be able to question it. These two things are foreign to ordinary people, and Descartes sees in the mass of non-scholars a public which will, through its intellectual naivety, have less ingrained defence mechanisms, and which will therefore be more receptive to the merits of his method. He trusts individual common sense, but not any form of popular wisdom, for the paths to truth are sometimes so twisted that it is more likely that a single man has found them than a whole people, despite the plurality of votes.

However, in its style, Descartes is fond of long sentences, with a lot of commas and semicolons, so that his sentences can be an entire page long. Reading them requires a certain intellectual dexterity and this does not seem to be of a skilful pedagogism for someone who claims to address the greatest number, the uneducated popular masses.


At the end of the treatise, Descartes explains that the consequences are demonstrated by the causes, but even more, he considers that the causes are also demonstrated by the effects. This assertion is indicative of a deterministic vision of Descartes. There is nevertheless a dichotomy in supporting determinism and making a distinction in nature between the soul, of a metaphysical order, and the body belonging to the physical world. Indeed, the soul commands the body’s actions and, therefore, it is the cause of its movement which is a physical phenomenon. Determinism, therefore, necessarily applies to the soul, whose manifestations then constitute links in the chain of causes and consequences. Two solutions therefore: either the metaphysical world is subject to determinism in the same way as the physical world, in which case the fundamental distinction that Descartes operates between the two loses its relevance, or the soul is part of the physical world and is therefore constituted of particles like what Lucretius described in On The Nature of Things. The question of the application of determinism to the soul joins the debate on free will, which has occupied so many philosophers of all ages since Saint Augustine.

Finally, we can see that Descartes does not mention miracles in his treatise, even though they are precisely manifestations of a metaphysical order in the physical world. The only occurrence of the word “miracle” in the Discourse refers to the timeless concept of the miracle of creation, suggesting that Descartes was not validating the notion of temporally localised divine intervention. However, he does not openly refute the miracles which were proof of divine power, but mostly the proof of the power of the Church, which claimed to be able to invoke them through rites or prayers. Seeing the risk of discussing miracles, he may have found it best not to broach the subject.

Portrait of René Descartes (painting by Frans Hals, circa 1649-1700)


The Discourse on the Method is the first book published by Descartes, in a context of intellectual coercion applied on philosophers by the Church. In opposition to authoritative religious dogma, Descartes was led to take precautions as to the content of the treatise and its mode of publication.

By publishing his method, he aims to offer a universal tool to reason, both for the study of the physical and metaphysical domains, with the aim of making philosophy a science as rigorous as mathematics. This is the foundation stone of Cartesian philosophy, and his work will influence the most eminent philosophers, including Immanuel Kant, Thomas Hobbes and Blaise Pascal. His scientific and philosophical aura over the centuries earned him the emeritus nickname of “father of modern philosophy”.