The existence of God has been a question since the idea of God was conceived Descartes tries to prove God's existence, and to show that there is without a doubt something external to ones own existence. He is looking for a definite certainty, a foundation for which he can base all of his beliefs and know that they are true. Descartes' overall project is to find a definite certainty on which he can base all his knowledge and beliefs.
Descartes attacks the principles that support everything he believes with his Method of Doubt. The Method of Doubt is Descartes' method of fundamental questioning in which he doubts everything that there is the slightest reason to doubt. Think about it like this. Almost everything you believe to be true comes from the senses or through the senses. However, the senses are sometimes deceptive. Since the senses are not completely trustworthy, it is irrational to place complete trust in them.
English: René Descartes, the French philosopher, ...
René Descartes
Statue of René Descartes with his famous statemen...However, it is no small leap of faith to presume that everything our senses tell us is false. In fact, it seems almost absurd to say such a thing. Nevertheless, as Descartes points out, we have dreams regularly and in these dreams, everything we experience is a figment of our imagination, or at least not real in the physical sense. So, it is reasonable to doubt everything our senses tell us, for the time being. Now, using similar logic, we can say that everything we have learned from physics, astronomy, medicine, and other such fields are all doubtful. Descartes even believed we could say that such simple, logical statements as 2+3 = 5 or a square has 4 sides could be conceived to be false. "Since I judge that others sometimes make mistakes in matters that they believe they know most...