Rene Descartes (1596-1650 CE) was a French mathematician, natural scientist, and philosopher, best known by the phrase 'Cogito ergo sum' ('I think therefore I am'). He published works on optics, coordinate geometry, physiology, and cosmology, however, he is mostly remembered as the "father of modern philosophy". He lived in a time preceding the Age of Enlightenment that flourished in Europe in the late 17th and throughout the 18th century CE, a period of revolutionary ideas in government, individual freedom, and religious beliefs. While not a direct participant in the Enlightenment, Descartes' legacy would be his influence on those who contributed to the scientific, political, and social changes throughout this age, an age of reason.

“I suppose therefore that all things I see are illusions; I believe that nothing has ever existed of everything my lying memory tells me. I think I have no senses. I believe that body, shape, extension, motion, location are functions. What is there then that can be taken as true? Perhaps only this one thing, that nothing at all is certain.”

― Rene Descartes