What Was the Cartesian Revolution?

The Cartesian Revolution describes how Rene Descartes, a 17th-century French mathematician and philosopher, helped shape a shift in thinking to skepticism from blind faith. He is perhaps most recognized for his statement, "I think, therefore I am," but his work in math, science and philosophy -- particularly substance dualism -- helped to move those fields into a more abstract realm.

It is uncertain how reverently Descartes adhered to Catholicism, but it is clear how his religious upbringing affected him. The church's main message was to simply believe in God without question but he could not do this without doubt. After questioning what was left once he doubted everything, Descartes found the existence of himself the only thing that survived. He reasoned that if he could question his own existence, he had to exist because there had to be someone doing the doubting.

This led to the dualism theory, also known as the mind-body problem. Descartes theorized that if he existed, it was in two different ways: as a mind, or a non-physical entity, and as a body, a physical entity. For him, the problem lay in bridging the gap between the two. There was obviously a relationship between the mind and the body's interactions, but it was unclear to him exactly what it was other than the two were separate and distinct. Even philosophers today like Daniel Dennett ("Brain in a Vat" thought experiment) and John Searle ("false dichotomy") still grapple with its implications. There has been no clear conclusion regarding the relationship between the mind and the body -- and the laws that govern it - -the way there has with something like a fever being the result of certain nerve fibers, called C-fibers, in the brain being activated.

Descartes' work in geometry also helped form the Cartesian Revolution. Using analytic geometry, he was able to bridge the gap between abstract algebraic formulas and concrete geometric curved lines. This laid the foundation for modern physics, a field in math that uses Cartesian geometry extensively to solve problems of speed, velocity and force, among many others. A real-life example is using abstract formulas to tell how planets orbit the sun or how to build a bridge.

Another key part of the Cartesian Revolution is Descartes' work in mechanical philosophy, the field of philosophy that reduces things such as heat, taste and weight to physical, measurable properties like size, motion and shape. This was revolutionary thinking because it brought into question the immortality of the soul. The church said that the soul existed both in a living body and once the body had died, but offered no other explanation.

However, despite mechanical philosophy's seemingly antagonistic stance toward the church, it led great physicists like Isaac Newton to discover laws of physics. The work that Newton did led to knowledge in gravity and the planets, the latter of which is important because of space exploration. In turn, Newton's studies indirectly led to Albert Einstein discovering other laws of physics, and it was Descartes who built the theoretical framework for both of them.

Though much of his science was later shown to have errors, Descartes invented the idea of inertia -- the principle of physics that discusses motion and resistance. He wrote his treatise, "The World," at a time when Galileo was being persecuted for going against the church's teaching that all heavenly bodies revolved around the Earth; as a result, Descartes' treatise was published after he died. In it, he described two laws. The first, called The First Law of Nature, states that if an object is still or moved, it continues that way unless something happens to it. The second, called The Second Law of Nature, said that if the object is moved, its motion is in a straight line; but if it is moved in a circular direction, it goes away from the center of the circle.

Although the math in his science may have had errors, the concept of inertia was important because it led to the laws of modern physics. Something like throwing a ball to another person may seem inconsequential, but it was Descartes who laid the groundwork for understanding the physics of this action. The ball, resting in a person's hand, stays still until an outside force -- the person throwing it to a catcher -- acts upon it; further, the ball won't travel in the same direction forever (as it would in space) because gravity forces it in a downward arc and into the receiver's mitt. Descartes' foundation for the modern laws of physics are found everywhere today, from simple acts like throwing a ball to figuring out how to travel outside the solar system.