In the third meditation Descartes attempts to prove that god exists using this argument. God is an infinite substance he has an absolutely independent existence. Human beings on the other hand are finite substances we do not have totally independent existence. This is the hierarchy of reality and is one of the basis’s for Descartes argument. Since god as an infinite substance is higher on the hierarchy of reality than human beings as finite substances. Due to the causal adequacy principle as applied to ideas which states that the cause of a idea must have at least as much reality as is contained objectively within the idea we as finite substances who have less reality on the hierarchy than the infinite substance of god can not be the origin of the idea of god. In fact the only one who has enough reality to create the idea of god according to hierarchy of reality is god himself. Therefore if god is the only possible origin of the idea of god and we have the idea of god than god must exist.
In the fourth meditation Descartes lays out his epistemological argument. The argument considers why god can not be a deceiver as well as explains Descartes account of judgment. God can not be a deceiver because god is all perfect and the will to deceive is an imperfection. Descartes account of judgment says that we must only make judgments on what we perceive to be clearly and distinctly true if we can not perceive something to be clearly and distinctly true we should refrain from making judgments and therefore our judgments will never be wrong.