René Descartes was a French philosopher, who lived from 1596 until 1650. He is considered to be one of the strongest influences on the Enlightenment movement. His most important quote is usually cited in Latin: cogito, ergo sum. This translates into English as “I think, therefore I am.”

Through this quote, Descartes is arguing the independence and uniqueness of the human mind and of humans in general. To him, the ability to think is proof of existence. In order to contradict Descartes, one could argue that not all thinking is necessarily free and therefore does not always prove independent cognitive ability. For example, if a person merely copies the thoughts of other people, simply making them their own rather than contemplating and developing them further, then their thinking is not free or independent, but merely a copy of others'. In fact, one could argue that in this instance no thinking at all is taking place. But does this then, following Descartes' philosophy, question someone’s existence?

However, this was not really what concerned Descartes. Descartes wanted to point out and prove individual existence, which was quite revolutionary at the time. Rather than simply following the doctrines of the Church and religion without questioning anything, as it had been promoted widely throughout the medieval centuries, Descartes found it important that humans should think on their own. To him, doubt is not necessarily negative, as doubt in itself is evidence of thinking. Thinking, in return, gives evidence of self and existence, as if a person didn’t exist, then they wouldn’t be able to think.