Rene Descartes: I Think, Therefore I Am
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Rene Descartes: I Think, Therefore I Am

Rene Descartes is most famous for his line "I think, therefore I am". Descartes was, however, also able to dissect that thought by using an exhaustive list of subjects including mathematics, physics, astronomy, anatomy, physiology, psychology, metaphysics, epistemology, ethics, and theology.

Joachim and Jeanne Brochard lived in La Haye, in the Touraine region of France. Jeanne gave birth to Rene Descartes on March 31, 1596. Unfortunately, Jeanne died a few days later of tuberculosis. Rene Descartes inherited the disease from his mother, exhibiting pale skin and weak behavior. The physician gave Descartes no chance for survival.

Fortunately for the world, Rene Descartes lived. Descartes received a Jesuit education at Jesuit College of La Fleche. At age seventeen Descartes went to the University of Poitiers. Descartes received degrees in civil and canon law. In 1618, Descartes became healthy enough to enlist in the army of Prince Maurice of Nassau.

During a campaign on November 10, 1619 Descartes escaped the cold weather by shutting himself in a heated room. In this heated room Descartes had visions. Descartes described flashes of light and thunder, leading to the formation of analytical geometry and the method of applying mathematical modeling to philosophy.

The Stanford Encyclopedia of Philosophy includes an entry by Gary Hartfield titled Rene Descartes. Hartfield writes the following concerning Descartes, “During the course of his (Descartes) life, he was a mathematician first, a natural scientist or ‘natural philosopher’ second, and a metaphysician third.” However, it was plain to see that Descartes played a bit in an exhaustive list of studies including mathematics, physics, astronomy, anatomy, physiology, psychology, metaphysics, epistemology, ethics, and theology. In the pursuit of knowledge, Descartes thought he should start with a clean slate. Descartes stated, “The chief cause of our errors is to be found in the prejudice of our childhood.” To avoid this, Descartes started out by doubting everything. Robert C. Solomon, author of Introducing Philosophy, states that Descartes “would accept as true only those things that were demonstrably true to him.”

Descartes needed to find one proposition that was beyond doubt. Descartes could not doubt his own existence, so he exclaimed one of the most famous thoughts in philosophy, “Je pense, donc je suis.” (I think, therefore I am.) He reasoned that doubt was a thought, and thought could not take place without someone to think it. This led to a century long Great Debate in Western Europe between faith and reason.

Descartes published many important works on geometry, philosophy, metaphysics, and more. These works include:

• the Discourse on the Method (in French, 1637)

• with its essays, the Dioptrics, Meteorology, and Geometry

• the Meditations on First Philosophy (i.e., on metaphysics)

• with its Objections and Replies (in Latin, 1641)

• the Principles of Philosophy, metaphysics and philosophy (in Latin, 1644

• Passions of the Soul, on the emotions (in French, 1649)

• Letters (in Latin and French, 1657–67)

• World, or Treatise on Light, containing the core of his natural philosophy (in French, 1664);

• Treatise on Man (in French, 1664 physiology and mechanistic psychology

• the Rules for the Direction of the Mind (in Latin, 1704

Descartes worked with techniques describing lines and mathematical equations of their ratios. This proved to be a powerful tool for calculations that were too complex for solving with compass and ruler systems. The algebraic geometry coordinates are now called Cartesian coordinates in recognition of Descartes. Descartes gave information to all on how to solve more intricate problems. His advice is simple. He suggested breaking large problems into smaller steps that can be completely understood.

Descartes accomplished unbelievable amounts of discovery for a single lifetime. He solved the problems of doubling the cube and trisecting the angle. He was the first to use the first letters of the alphabet for known identities, and he used the last letters in the alphabet for unknowns. He discovered the law of refraction. Descartes made detailed studies of great forces being exerted by small efforts. Examples of these exchanges in force are the pulley, lever, vise, and wedge. He had impact with Pascal and the principle of decreasing atmospheric pressure with increasing altitude.

The accomplishments go on and on. He had successes with animal dissections. Descartes had experiments with reflex action including eye winks. He studied human emotions including the fight or flight response. He calculated the angle of refraction for optics. “He solved the problem of spherical aberrations in telescopes, and designed lenses with elliptical or hyperbolic curvature free from such aberration.”

In 1629 Descartes worked on a set of parhelia, false suns. He explained that they were images created by a large ice-ring in the sky. The ice-ring acted as a lens to form the parhelia image. Upon reporting this discovery, Descartes decided to explain all phenomena of nature. The work would be in three parts: light, man, and the soul. The first two: Treatise on Light and Treatise on Man were completed. It is unknown if Treatise on the Soul was ever written. The soul involving areas of religion would have been very controversial. At this time, in 1633, Galileo had been condemned by the Catholic Church for his “heretical” works.

Descartes had a daughter, Francine, in 1635. The mother was Helena Jans, Descartes housekeeper. Francine died in 1640. Descartes paid a wedding dowry for Helena in 1644. Descartes was working on his principles of physics. In November 1639, Descartes sent a copy of Meditations to Mersenne and asked for twenty to thirty of the top theologians for objections. Descartes published this work with the objections and his replies.

After Meditations, Descartes worked on Principles. The Principles was a complete works on physics. Descartes related the various parts of philosophy using the form of a tree:

Thus the whole of philosophy is like a tree. The roots are metaphysics, the trunk is physics, and the branches emerging from the trunk are all the other sciences, which may be reduced to three principal ones, namely medicine, mechanics and morals. By “morals” I understand the highest and most perfect moral system, which presupposes a complete knowledge of the other sciences and is the ultimate level of wisdom.

Descartes work Discourse on the Method contained three parts. The third part of this work is La Geometrie. This work introduced modern algebra notation. The work was perhaps the first to use both positive and negative quantities. Modern exponential notations are introduced through this work. Burton writes, “Descartes broke with Greek tradition by divorcing numbers from a reference to physical quantity.” Descartes devised an algebraic method for obtaining the normal.

In closing, the total sum of Descartes works in incredible. There is a descriptive saying of a dabbler “jack of all trades and master of none.” Descartes was a master of all trades that he sought to work with. Descartes is one of the greatest mathematicians, philosophers, physicists, and more of all times. Descartes had no doubt that he existed. The world, no doubt, is better for it.

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The Scientific Revolution Changed the Way Europe Viewed the Universe Medicine and Thinking...

Picture Sources

Descartes Painting

Illustration in Latin: Brain

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Comments (16)

Descartes once walked into a bar and the barman asked him if he wanted a drink. "I think not" said Descartes before vanishing instantly. lol (sorry about that joke - couldn't resist) Very interesting write about a truly remarkable man. :)

Fascinating article; I'm not so sure I like Descartes for devising algebra, though! Cute joke, Alistair.

Another finely written article of history Lauren. Very thorough narrative of the facts on a true genius. Great work.

Ranked #1 in Philosophy

I like Rene Descartes. It's the art of thinking that differ human beings to each other.

"Je pense donc je suis". A great tribute to a great man. Bravo Lauren.

Ranked #7 in Philosophy

A philosopher indeed. Good write Lauren. SU'd.

Very nice work.

Not Descartes

"He solved the problems of doubling the cube and trisecting the angle."

If you mean doubling the cube and trisecting the angle using ruler and compass, then this is not true. Mathematicians proved much later (19th century) that this is impossible.

Otherwise a great article!

The satnav principle teaches oneself direction to avoid hazardous roads in all aspects without that direction all roads will lead to nowhere when you dont know what direction your journey needs to be heading we encounter hazordous roads barriers etc my question is this is it possible to focus on all of mother nature without allowing viruses by way of suggestion to penartrate the fathers purity and clarity free from suggestion to the mentaly challenged

Thanks for the fascinating read! The whole "doubling the cube and trisecting the angle" thing is lost on this mathophobe. Descartes, as well as great Renaissance thinkers like Da Vinci, amaze me with their cross-discipline genius. Maybe it was their curiosity about everything in life, as well as ignorance of the whole left-brain / right-brain thing we're so hung up on these days, that made them so brilliant.

Ranked #3 in Philosophy

@Not Descartes I wasn't implying using a compass or ruler, which is why it's not stated within that paragraph.


Descartes was not actually the first to say "I think, therefore I am." The phrase itself was introduced in a response to his meditations. Descartes original wording is (pardon me, I don't have access to the french right now)

"and here I discover what properly belongs to myself. This alone is inseparable from me. I am--I exist: this is certain"

In the published responses often found at the end of editions of his meditations you can find the first use of the phrase.


You forgot to mention how his dualism (which was based on the presupposition of a god existing) infected philosophy for 400 years...

Seen as graffiti on a table at Lovejoy Library, Southern Illinois University - Edwardsville. "I drink, therefore I am."

Rene' Descartes

The root mening of the word consciousness is cogito, so,

I am consciously aware, therefore I am.

I should know, I wrote it, and I know what I mean.


Excellent. Sorry, I'm out of votes