René Descartes (1596–1650) was a French philosopher, mathematician and natural scientist. During his lifetime Descartes came up with a completely new way of studying philosophy which broke with the old traditions of the ancient Greek philosophers. For the first time, it set out a method for working out which things were certain, using a process of reasoning which left no room for doubt. His way of thinking became known as Cartesian philosophy, and it changed the way people studied philosophy and natural sciences forever. Because of this, Descartes is considered to be the first modern philosopher in the West. In mathematics, his work laid the foundations for the study of calculus, and linked algebra and geometry for the first time.​​​​​​

Early life

René Descartes was born on 31st March 1596 in the small French town of La Haye en Touraine. His mother died when he was born, and his father was a member of parliament. As a child, he suffered from ill health and did not start school until he was 10 or 11 years old. His father wanted him to become a lawyer, and after school, Descartes went on to study law at university. But afterwards he moved to Paris, where instead of starting work as a lawyer he spent time meeting people, gaining new experiences and learning about the world.

Dreams

After two years Descartes joined the Dutch army, where he studied military engineering, specializing in mathematics and physics. One night in 1619 he had three dreams, in which a “divine spirit” seemed to reveal to him a new approach to studying philosophy. He realized that some of the methods used to tackle mathematical problems could also be used to answer philosophical questions. Descartes suddenly saw that all the certain things—truths—we could discover about the world were linked back to a few basic truths. If these basic truths could be worked out, then they would form a foundation for others to be worked out using logic, and answered for the first time with certainty.

Reason

This was an entirely new way of doing philosophy. At the time, philosophers followed the method of the ancient Greek philosopher Aristotle, believing that the best way to explain things about the world was by making observations with the senses. Descartes thought that this was an unreliable way of doing philosophy, because everyone’s senses are different; it meant that everyone could argue different things. He wanted to replace it with an orderly, systematic method, based on things which could be proved without doubt. This was the beginning of using reason, and it would change the study of philosophy and natural sciences forever.

"I think, therefore I am"

Descartes left the military and worked on his ideas, taking classes in mathematics and astronomy, and travelling across Europe to meet other mathematicians and philosophers. In 1628 he settled in the Netherlands, where he began work on his first major book, setting out the “rules” for his new method of doing philosophy. He knew these ideas would be unpopular, and fearing persecution from the Catholic Church, he did not publish them until 1637.​​​​
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Later life and death

Over the next ten years, Descartes went on to rewrite almost everything that was already known about philosophy. In 1644 he published his major work Principia Philosophiae (Principles of Philosophy), which described how the entire Universe could be studied using mechanics: a method used in mathematics. By 1649 he was one of the most famous scientists in Europe.

​​​​​​​​​​​​​​His final work The Passions of the Soul (1649) was about the part that emotions played in philosophy. It was inspired by letters exchanged with a felllow philosopher, Elisabeth of Bohemia. Descartes then took up a job in Sweden, where he worked in the court of Queen Christina. Here, he died from pneumonia within weeks, perhaps because of the cold or the Queen’s demanding daily schedule.