In meditation III, Rene Descartes says that he is certain that imagination and perception do exist since they exist inside his mind as consciousness modes. However, Descartes says that he can never certain whether his perceptions and imaginations have any truth basis. He expounds on his argument about God's existence from the discourse. Descartes analyzes his mind so as to know whether there exists anything that would let him make God up. Descartes realizes that he is finite compared to God who is infinite, perfect and all powerful. His argument says that it's impossible for a being like him who is to dream about infinity and he thus concludes that the idea of infinite has to come prior to the idea of being finite or prior to any person's thought of what he or she is.
There exist three kinds of ideas; innate ideas, factitious ideas and adventitious ideas. The innate ideas are those thoughts that are and have always been within us, the factitious or invented ideas on the other hand are the thoughts that arise from our imagination, while the adventitious ideas are the thoughts that arise from the world experiences. The idea of existence of God is an innate one and must have been placed inside us by a supernatural being that is, God. There is no way that the idea of God's existence can be an invented one or an adventitious idea. Nothing comes from nothing, so everything must have come from something. The cause of any idea has to have leastwise much proper or formal reality as it has an intent or objective reality. Inside a person like me there exists an idea of a supernatural being referred to as God, and this is an infinite objective reality.
As a human being who is finite, I cannot be the cause or origin of this idea, because I am not an infinite and am also not a perfect being. Another reason is that; as a person, I lack adequate formal reality and only an infinite and a perfect supernatural being is capable of causing such an idea. That is why, God, who is possess infinite objective reality must be in existence so as to be the source of my idea about God. Since in my idea, the supernatural being or God is absolutely perfect, he has to be a benevolent being. Benevolent beings do not lie and God being so, he would never mislead me and He would not allow me to error, and if I did, he would give me a way for me to correct my errors.
For me to have any idea, first I have to exist, which I do and my existence has to have a cause or reason. The possible definitive causes of my existence can only be I or my always having been in existence, my parents who are some beings that are less perfect compared to God, and God Himself. This is a very valid argument because, if it was not, then I ought to have created myself, which I did not and if I created myself, I would have created myself being perfect. Since I was created, then I am a dependent being and thus, I have to be continuously sustained by another being that is more superior. Also, the idea in me that perfection exists, must have arisen from a perfect being, therefore God exists.
Descartes argues that he has a perfect and trenchant thought of God. In a similar manner cogito is axiomatic, so is the existence of God, as his impeccable idea of an impeccable being could not have been brought about by anything to a lesser extent than an impeccable being. If an individual exists, then there must be a source for his or her being. Descartes talks about the likelihood that an individual is answerable for his or her being. He further argues that this cannot be a possibility because of the concept that if humans created themselves, in their own image, then, they would not have created all the lure, deception and sin that presently continues to trouble humanity. If humans created themselves, they would make themselves to exist without nuisance or suffering.
The other argument that hints that God exists brings forth the idea that people have at all times existed. Descartes invalidates the argument since, an individuals' existence presently cannot reflect that individual's previous existence. It is ignorant to presume that just because we have always existed, that it is an adequate explanation for our origin. Only a lazy philosopher can come up with such an argument and he must not have cared enough to dig for answers. Explaining the existence of God by mentioning an individual's parents, could have been done by a lazy philosopher who never researched for more answers. An individual's parents got their children to this world through the birth process which is an enough physical explanation on how human beings come to exist. Just as Descartes explains, there exists something beyond the assumption on the physical explanation of the existence of human being and that this explanation causes an infinite regress. This can be evident when one researches an individual's family tree one would keep on being referred to another parent and another parent and another parent. This could continue endlessly because human beings have existed for a very long time and thus it is okay to conclude that a human alone cannot be responsible for the existence of the entire human race. Also, if the tracking of individuals went back long enough, they would get to the Supreme Being who created Adam and Eve as they are known as the first parents.
Descartes views that it is necessary to establish that there exists God and that he cannot be a cheat in so as to take away some of the basis for doubt (36). Descartes argues that the historically acknowledged "cosmological argument is itself is misleadingly simple, but it depends upon a set of eminences and terms. So when one misleads an individual other than oneself, it is being done for the sole purpose of gaining in one's own interest. God is all knowing, the creator of all things and is in control of everything that has happened in the past and things that will occur in the future. For those very reasons there is no reason from him to deceive anyone because there is nothing more for him to gain. (32) Humans fall into error because of our souls. If our souls are the source of light and matter is the source of evil. Then a being like God - "evil demon"- would be just as equal as our "evil genius". These could make him believe that what he grasps clearly and distinctly is true when in reality; there is no truth about it.
Descartes argues about res extensa as well as res cognitans. He says of himself as a thinking being and further says that res cognitans can come into being because if a pair of trenchant things can be formed, res cognitans can be formed individually from an essence, and that essence is the res extensa. On the other hand, the material constituent is the crux of the res cognitans. Most probably the mind is well off with an extension or esence. Res extensa is a thing of extension since it is res cognitans' place. The evidences for the being of God are determined by distinguishing res cognitans from res extensa. Normally, God does not possess res extensa but possesses a soul that is worth to be the creator and origin of other lives, and the all caring and loving being. At some stages, res extensa or extension assists res cognitans, but it usually happens that res cognitans independently exists. When a person dies from this universe the res cognitans is conveyed to a different universe as the res extensa is not alive and it encounters little or nothing or does nothing. Thence, the constructs of res cognitans and res extensa evidently winds up the best proof that God exists; Rene Descartes is successful in proving the existence of God.