Descartes and dualism"I think therefore I am", the famous quote by René Descartes, is the basis of his theory known as dualism. The mixture of mind and body or res extensa (extended substance) and res cogitans (thinking substance) shows Descartes' ideas of a "true human being" (Cottingham 7). Known as the father of modern philosophy, Descartes realized that you could not simply analyze a problem at the level of common sense, but that you had to “probe at the micro level” (Cottingham 4). Through his technique of doubting everything he believed to exist and establishing a new philosophy, Descartes discovered that without a doubt the only thing he could truly believe existed was his own mind. Then he supposed that a demon was deceiving him into believing what he saw. With this idea, he concluded that "all external things are merely the delusions of dreams" (Descartes' Meditations, quoted in Cottingham 23) that the demon has devised. Being able to convince oneself of one's own ideas and being able to allow oneself to be deceived b...