Rene wanted to break with the philosophy of the past, along with its traditions, authority, vagueness of language, and uncertainty. He probably had in mind the particular philosophical system of the scholastics, which followed in line with Aristotle (in some respects).
Descartes was a rationalist, which means he trusted merely his naked reason for the creation of his own philosophical system (or, system of knowledge). In other words, he did not rely upon the faculty of his senses/perception. He felt that the senses could be very deceptive. One of Descartes’ main aims in his search for knowledge was a system of knowledge that would conquer skepticism, or the idea thereof. Another of his aims was to bridge the gap between appearance and reality. A common question in this area can be asked: “How can I know what is in the external world, really is that which I see or observe it to be?”
As a mathematician, Descartes had a bent toward deductive reasoning; and thus, he had the inclination to develop a system of knowledge that fit logically together. In this system, for instance, a person could come to the same set of hypotheses and propositions in the same order in which Descartes had laid them out, and come to the same conclusion as did Descartes.
The method by which Descartes aimed to arrive at knowledge has been called methodological doubt. In this method, he used a priori deductive reasoning. Descartes counted as knowledge those things that he could know with certainty. In other words, if there was something in his view that could be doubted, he did not trust that thing as something which could be known. So, in the formulation of his system of knowledge, he began by doubting everything – from the things he had previously learned in philosophical systems to his present environment and personal state of being. The one thing he found that was indubitable was his thinking process. This “knowledge/certainty” led him to the doubtless knowledge of his own existence. This particular breakthrough of his thinking process has been dubbed, “I think, therefore, I am.” Since Descartes became certain of his own existence and the knowledge of his being a thinking-being, he began to reason from this particular knowledge of himself outward.
So, since he could trust that he was himself was a thinking-being, and that he existed, he could then begin to deduce from these certainties other things, including God. This seems to be where Descartes’ method begins to show its apparent flaws. He said something to the effect of:
“I think there is a God, because I believe that God is good. Since God is good, he would not deceive me into believing he exists.”
This line of reasoning, however, seems misguided.
Without metaphysical foundations, Descartes’ method FAILS. He jumps from the certainty of his own existence to the certainty of God’s existence. He reasons from the lesser being to greater Being. Descartes should not have broken away from the past traditions of theology/philosophy, which bound faith and reason together. Instead of keeping with the tradition of Augustine and Aquinas in saying something to the effect of: “I believe in order to understand,” Descartes holds himself in higher authority by saying something to the effect of: “I understand in order to believe.” He holds revelation over against reason instead of reasoning within the bounds of revelation. In attempting to develop an epistemology without metaphysical foundations, Rene Descartes, much like Nietzsche, seems to (though, unknowingly) have wiped away the sun and everything with it from the horizon, that we may have no other choice to re-orient ourselves with a life and a reality without God as our foundation – only to be left with ourselves as gods to determine that which is good, acceptable, and perfect.