["Portrait of Rene Descartes," by Franz Hals, taken from Wikipedia.Com; this image is in the public domain.]
Reposted from Quora
It is impossible to overestimate Rene Descartes' contribution to the modern mind. As the US left the Bretton Woods agreement, Then-President Richard Nixon was reported to have remarked,“We're all Keynsians now.” Well, in the centuries following Descartes' life and work, one might as well remark “We're all Cartesian now.”
After having attended University, Descartes spent his youth traveling and engaging in military service and eventually chose to take some time in solitude to apply his education and life experience toward determining what could be said to be undeniable truth. This period of solace led him to apply a process of radical doubt to what he believed to be true. In this process, what he came up with as the standard for knowledge was the underlying basis for the scientific method.
Science, as we know it today, is a Cartesian project, as is the field of statistics, and most other modern intellectual fields. Nearly every major philosopher of the next two centuries accepted the Cartesian premises about what is required for knowledge (although the rationalists and empiricists took different emphases in the application of those premises). It wasn't until the post-modern movement that any serious challenge was posed to the Cartesian method.
This approach towards knowledge has become so ubiquitous, that most people apply it without having any understanding of where it comes from. Any time you hear someone ask for someone to produce data to support their point, understand that they are appealing to the Cartesian method. Any time someone invokes modern science, remember that that comes from Descartes. Anytime anyone invokes radical doubt as an intellectual starting point, remember that they are invoking Descartes.
Descartes is easily one of the most important philosophers of all time, and most people don't even have any idea the extent to which they continue to be influenced by his work.