Rene Descartes purposely identifies his work as "a meditation" and presents his thoughts using the first person. He doubts everything that he has admitted to up until this point because he feels that the senses can be deceiving. The senses, according to Descartes, were bad indicators to what is real because one, there is the chance of error and two; the actual experience of dreaming is misleading. Descartes thought that by doubting everything and anything, he could erase all other knowledge and begin to build from the base up. This idea is like an architects", being that they must have a solid foundation before they can proceed. His ideas were very systematic, similar to those used by scientists and rational simply because he did not want to just add to things done earlier by others. .
He began with the determination to doubt all and take nothing for granted. While doing so, he stumbled across one proposition that he could not doubt. And that was his own existence. He stated that after all, the simple act of doubting presupposed something, which was engaging in doubt. This famous proposition is known as "cogito, ergo sum": I think, therefore I am. .
Descartes concluded from this that at least one existential truth existed that we can claim to know. This was, that we, as individual persons, exist as thinking beings. It is on this premise that he attempts to base anything else because he felt that any secure philosophy must have a strong and secure starting point. It is from this point that he attempts to prove the existence of god and other things, which he thinks he can deduce. .
Following Descartes" doubts of the senses he begins to doubt mathematics. He states the "Evil Genius Hypothesis." This bold new idea states that maybe god is evil and that there is a higher being who likes to deceive others. With that in mind he states that this deception implies two things. First it implies that Descartes believes and secondly that Descartes is.