Rene Descartes, 1596 - 1650, French.
Born into an aristocratic family.
Throughout his life, Descartes was a devout Roman Catholic committed to the authority of the church.
As a child, he earned the name "little philosopher" because he was continually inquiring about the ways of the world, why was this, and what's that.
After he turned 6 years old, he was sent to a Jesuit College, for sons of the nobility.
He was not known as an early riser in the mornings and had a special privilege, as was appropriate for the son of a nobleman; he was allowed to stay in bed in the mornings.
Younger Rene Descartes
At the college, he had a memorable experience that he will never forget: the college received the heart of the assassinated Henry IV.
For the first 5 years of college, students studied the humanities, followed by mathematics in the last year.
After he left school, he devoted his time to learning the essential skills of horse riding and fencing, as required of a son of a nobleman.
Travelling was also a priority, and for a number of years, he visited many countries in Europe, especially the Netherlands, where he stayed for long periods and visited frequently, he enjoyed the liberal social conventions and relative freedom as compared to Europe. He had a liking for the Netherlands in particular and joined the army and trained as a military engineer.
Descarte's Europe
From his school days, he knew that the languages he had studied at college would enable him to read the thoughts and dreams of some of the greatest ancient authors. There was a need to read about the myths to understand their meaning, to study their histories, to understand their motivations and aspirations.
Eventually, in 1629, Descartes started to ponder the world about him, by studying astronomy and optics, and his deliberations were recorded in his book "Monde" (world).
His brother Pierre was not impressed with Rene. Pierre considered it a disgrace for Rene, the son of a nobleman, to be besmirching the good name of the family by associating with activities like science, mathematics, and philosophy. There was even an attempt to disinherit him.
His grandchildren became reconciled because G'Dad brought great honor to the family.
Nevertheless, in spite of the disapproval of his brother, Descartes continued his work and study of science and Mathematics.
But Descartes was living at a time of significant turmoil, at the dividing line between medieval and modern Europe. Old understandings and authorities were being challenged, and scientific and mathematical ideas proliferating across Europe as never before, to the deep concern of the Church. The Inquisition would endeavor to staunch the flow of this material, but eventually, it was overwhelmed. Galileo's views on the place of the earth in the system of stars were declared blasphemous and heresy, and the Church refuted them by appealing to Pythagoras (500 BC).
Rene Descartes
By 1632 Descartes had developed his ideas on the principles of physics and astronomy and was contemplating having his book "Monde" published.
He intended to publish it anonymously, perhaps so that he could deny ownership if it did not meet the requirements of the inquisition.
Fortunately, before committing to the printing, he became aware of the proceedings against Galileo.
Galileo was teaching and writing under the protection of the Duke of Tuscany.
After Galileo had published his book "Spots on the Sun", suggesting the earth moved about the sun, the congregation of the Inquisition denounced it as absurd and false and drew on the teachings of Pythagoras to refute the ideas.
Under threat, Galileo withdrew his claims of the earth moving around the sun, and a formal decree was passed by the Inquisition, which was greeted with ridicule internationally.
Later, Galileo decided to withdraw his compliance, and recklessly published his "Dialogues on the System of the world, according to Ptolemy and Copernicus". It was received with applause by the wider public, but the Inquisition did not like it.
Galileo was arrested and charged with heresy.
The Grand Duke was able to protect him from the worst excesses of the Inquisition, but he was imprisoned for 3 years, and after his release, banished to the country.
All these proceedings caused Descartes to reconsider his position, He decided he would not publish his findings that the earth revolved around the sun, if it was against the authority of the church.
Sometime later he was given a copy of Galileo's book and found similar conclusions to his own.
Subsequently, he published his "Principles" in which he still will not say the earth revolves around the sun, but is carried along by a larger vessel, similar to a person on a boat; the person is stationary but the boat moves.
Descartes was a man of many parts, and perhaps foremost, he was a philosopher well known for the one-liner "I think, therefore I am".
He also made a study of light, and one of his books, "The Treatise on Light" shows the extent of his studies. He revealed the laws of reflection and refraction of light. He made drawings of how the lens in the eye refracts the light. The rainbow was also thought to be a result of the light of the sun being reflected and refracted through the water drops.
In Mathematics he unified the methods of algebra and geometry, into what is now known as Analytical Geometry.
Analytical Geometry
This graphical picture was vital for the development of differential calculus, as presented by Newton and Leibniz.Also significant in mathematics was his notation; he used x,y,z, etc., as the unknown and a,b,c, as the knowns.
Another notation was the practice of using a superscript to indicate a power. For example, instead of writing x square, he would write x² and instead of y cubed, y³
All these innovations are standard practices in modern mathematics.