Discourse on Method

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The Discourse on the Method is a philosophical treatise published by René Descartes in 1637. Its full name is Discourse on the Method of Rightly Conducting the Reason in the Search for Truth in the Sciences (French title: Discours de la méthode pour bien conduire sa raison, et chercher la verité dans les sciences). The Discourse is best known as the source of the quotation "Je pense, donc je suis" ("I think, therefore I am"), which occurs in Part IV of the work. (The similar statement in Latin, Cogito ergo sum, is in §7 of Principles of Philosophy.) In addition, one of the works published with it, La Géométrie, contains Descartes' introduction of the Cartesian coordinate system.

The Discourse on the Method is one of the most influential works in the history of philosophy and science. It is a method which gives a solid platform from which all natural sciences could evolve. In this work, Descartes tackles the problem of skepticism which had been revived from the ancients such as Sextus Empiricus by authors such as Michel de Montaigne. Descartes modified it to account for a truth that he found to be incontrovertible. Descartes began his line of reasoning by doubting everything, so as to assess the world from a fresh perspective, free of any preconceived notions.

The book was first published in Leiden in French, together with his works "Dioptrique, Météores e Géométrie". Later, it was translated into Latin and published in 1656 in Amsterdam. With Meditations on First Philosophy (Meditationes de Prima Philosophia), Principles of Philosophy (Principia philosophiae) and Rules for the Direction of the Mind (Regulae ad directionem ingenii), it forms the basis of the Epistemology known as Cartesianism.


  1. How to think correctly
  2. The Method of Science
  3. Morals Maxims deduced from this Method
  4. Proof of God and the Soul
  5. Physics, the heart, the soul of man and animals
  6. Experiments

How to think correctly

"Good sense is, of all things among men, the most equally distributed ... the diversity of our opinions, consequently, does not arise from some being endowed with a larger share of reason than others, but solely from this, that we conduct our thoughts along different ways, and do not fix our attention on the same objects. For to be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it."

In the 'building metaphor' used by Descartes, our opinions and thoughts are the ground upon which our perceptions are built. Descartes remarks on the sedentary nature of ideas and opinions, saying “I firmly believed that in this way I should much better succeed in the conduct of my life, than if I built only upon old foundations, and leaned upon principles which, in my youth, I had taken upon trust.” In other words, the core principle is that one must not seek to build on old foundations of knowledge, but should look for other fertile land to build knowledge upon.

The Method of Science

Descartes Discourse on Method fits in a long row of scientific methods in the history of scientific method.

The four precepts

The following quote from Discourse on Method presents the four precepts that characterise the Method:

1. "The first was never to accept anything for true which I did not clearly know to be such; that is to say, carefully to avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of doubt.
2. The second, to divide each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution.
3. The third, to conduct my thoughts in such order that, by commencing with objects the simplest and easiest to know, I might ascend by little and little, and, as it were, step by step, to the knowledge of the more complex; assigning in thought a certain order even to those objects which in their own nature do not stand in a relation of antecedence and sequence.
4. And the last, in every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted."

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The first step comes from realizing that everything you know might be wrong. After all, he notes, a man can have lost his arm and still feel it. Could it be that we are all deceived about everything? The first step then is to doubt everything, and only trust that which you can not rationally doubt. Originally, the only thing he decided to believe was "I think, therefore I am". After this, he decided that at least the evidence of the senses is clear and distinct and rich in detail in a way that dreams and illusions seem not to be. Even if he could feel the arm, he could rely on a wealth of other information to realize that the arm was gone.

The belief that remains after the first step is what we can work with in step two.

The enumerations in step 4 have developed into many forms. He suggested drawing boxes on a paper, and connecting them. This idea has led to many graphic thinking aids that we use today, for example diagrams, cartesion coordinates, and a wealth of methods that derive from using coordinates and Bayesian charts.

Morals, and Maxims accepted while conducting Method

The following three maxims were adopted by Descartes so that he could effectively function in the 'real world' while experimenting with his method of radical doubt. They formed a rudimentary belief system from which to act before he developed a new system based on the truths he discovered using his method.

  1. Obey the laws and customs of my country and religion
  2. Be as firm and resolute in my actions as I was able
  3. Endeavor always to conquer myself rather than fortune, and change my desires rather than the order of the world, and in general, accustom myself to the persuasion that, except our own thoughts, there is nothing absolutely in our power; so that when we have done our best in things external to us, all wherein we fail of success is to be held, as regards us, absolutely impossible.

Descartes uses the analogy of tearing down the house to its foundation in order to build a secure edifice; he even extends the analogy to move next door into a house of morality, while his own house is being rebuilt.

Proof of God and the Soul

Applying the method to itself, Descartes challenges his own reasoning and reason itself. But Descartes believes that three things are not susceptible to doubt, and these three support each other to form a stable foundation for the method. He cannot doubt that something has to be there to do the doubting (I think, therefore I am). The method of doubt cannot doubt reason as it is based on reason itself. By reason there exists a God, and God is the guarantor that reason is not misguided.

Perhaps the most strained part of the argument is the reasoned proof of the existence of God, and indeed Descartes seems to realise this as he gives three different 'proofs' including what is now referred to as the negotiable ontological proof of the existence of God. Some argue that Descartes inserted his statement on the existence of God in the Discourse on Method to appease censors of the time; a very serious concern, as within Discourse Descartes points out that he was at first reluctant to publish the work because of the recent show trial of Galileo by the Roman Catholic Church in 1633, just four years earlier.

Physics, the heart, the soul of man and animals

Here Descartes describes how he in other writings discusses the idea of laws of nature, of the sun and stars, the idea of the moon being the cause of ebb and flood, on gravitation, going to examine light and fire, and goes on to medicine, the motion of the blood in the heart and arteries. He describes that these motions seem to be totally independent of what we think, and concludes that our bodies are separate from our soul.

He does not seem to distinguish between mind, spirit and soul, which are identified as our faculty for rational thinking. Hence the term "I am thinking , therefore I am." All three of these words (particularly 'mind' and 'soul') can be identified by the single French term âme.


"Experiments, that they become always more necessary the more one is advanced in knowledge; for, at the commencement, it is better to make use only of what is spontaneously presented to our senses"

"First, I have essayed to find in general the principles, or first causes of all that is or can be in the world"

Secure on these foundation stones, Descartes shows the practical application of 'The Method' in Mathematics and the Sciences.

Influencing future Science

One practical method was to order the objects in different ways on paper to make them easy to see clearly. This became the basis of the Cartesian coordinate system, the Histogram and Analytic geometry. These ideas influenced Isaac Newton and Gottfried Leibniz in their development of calculus.

The most important influence, however, was the first precept, stated by Descartes as "[To]never to accept anything for true which I did not clearly know to be such". This new idea of skepticism influenced many to start finding out things for themselves rather than relying solely on authority. This idea might be considered to be the starting point for the development of modern science.

This skepticism not only influenced the 'hard' sciences, but is also considered the start of modern philosophy. Later philosophers adopted Descartes' doubt with a vengeance. Most prominently, David Hume doubted the concept of causality and was unable to "clearly know" it to be true.

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