In the fifth Meditation, Descartes presents his second argument in favor of the existence of God. Descartes argues that existence is perfection and therefore can be a predicate of God. I will explain first what is the ontological argument for the existence of God. Next, I will discuss why Descartes decides to introduce God into his philosophical method. I will therefore try to argue that existence is a perfection and that, as a predicate of God, existence reveals some truths about God. The ontological argument seeks to demonstrate the existence of God from an a priori perspective, that is, from idea implanted in the human mind by God himself. The argument therefore depends on analytical reasoning, from the premise to the conclusion. Descartes believes he has an innate idea which he calls “innate” (p. 43). His ability to think was not the cause of the idea in his mind, but of God's free will to act. Thus, as the idea manifests itself to his mind intuitively; reveals something about its author. The idea allows Descartes to think of a perfect being that must necessarily exist, namely God. In his epistemological search for truth, through thought experiment, Descartes' Meditations offer the reader a method of doubt that could be used to discover what is absolutely certain and free ourselves from errors caused by incorrect assessments. Descartes' aim is to find the indubitable truth. He uses the method of hyperbolic doubt to establish an absolute and convincing foundation of truth. He discovers that sensory experience can be doubted, but Descartes cannot doubt that he actually doubts. Furthermore, he fears deception about everything. However, he cannot be deceived about his own existence because to be deceived one must first exist. “I think, therefore I am”. I... in the center of the paper... a triangle includes three sides, so the idea of ​​God includes His existence. Since Descartes was able to prove the existence of God, he believes that man can have confidence in his clear and distinct idea and reason. Since God is perfect, He cannot be a deceiver; if He did, it would undermine His nature. Therefore, the rational mind can now be assured of clear and distinct truth. Works Cited Beardsley, Monroe C. European Philosophers from Descartes to Niectzsche. New York: Rondom House, Inc. 2002.Holt, Tim. “Existence is not a predicate.” ©2008. Accessed: Access, November 8, 2011.http://www.philosophyofreligion.info/Robinson, Timothy A. God. 2nd edition. Indianapolis: Hackett Publishing Company, Inc. 2002. Ross, Kelley L. “The Beginning of Modern Science.” ©2010. Web.Access, 12 November 2011. 2010http://www.friesian.com/hist-2.htm#descartes