By determining his deceiver as an evil demon, Descartes rules out God. He asserts, "God would not let me be deceived" about bodies or mathematics and geometry since God is supremely good. But since Descartes is clearly deceived, "evil demon" is a possible argument in providing doubt for his previous opinions. .
Descartes confirms that he could be deceived about his senses, mathematics and geometry and extended bodies. In Meditation 2, Descartes seeks to determine what (if anything) can be known beyond any doubt. Descartes resolves "after thoroughly thinking the matter through I conclude that this proposition, I am, I exist, must be true whenever I assert it or think it." Even if one is deceived, one must exist as a thinking being in order to be the subject of deception. Descartes establishes himself as a thinking thing and based on the "natural light of reason," where the total cause of something must contain at least as much reality as does the effect, Descartes believes that he could not have convinced the idea of something perfect, being that he is imperfect. Descartes could not have originated the idea of God on his own. He claims that his idea of an infinite substance like God must come from some substance that is itself infinite. Therefore, God must exist as the source of Descartes' idea. Descartes also imagines that God exists as a perfect being. His idea of God is a substance that is "infinite, eternal, unchangeable, independent, supremely intelligent, supremely powerful" which created him and everything else that exists. Descartes reasons that God is perfect and cannot be a deceiver as that would be an imperfection. He claims God would not deceive him about his clear and distinct ideas of the world of external bodies, thus, establishing that bodies are extensions in space that interact or are generated by mathematics and science.