René Descartes, French philosopher and mathematician, is generally regarded as the father of modern philosophy for establishing a beginning point for human existence, states Biography.com. His famous line, "I think; therefore I am" implied that being human requires a distinct core apart from all other matter in the universe and the ability to evaluate situations and concepts mentally.
Descartes' ideas were markedly different from general human understanding during the early 17th century, according to Biography.com. His approach to philosophy was to clear the slate of preconceived beliefs and then add only those things about which it was possible to be certain. The first of these notions was simple human existence.
Biography.com reports that Descartes believed all truths were connected. Using his mathematical background, he sought to prove this was true through rational means.
Sam McNerney of Big Think explains that Descartes highly valued skepticism and reason, both of which he emphasized in his written work "Discourse on the Method." In it, he wrote that truth is available to those who apply both reason and skepticism to reality. At the time, this was not a commonly held belief. In fact, in the early 17th century most Europeans believed consulting with oneself was pointless, as God revealed all.