He first determines that human knowledge is based entirely too much on unproved presuppositions. He argues that this makes it difficult to distinguish between truth and error, since we cannot recognize true knowledge. Descartes proposes that the quest for knowledge must be based upon universal doubt. Specifically, he proposes the following in relation to his universal methodic doubt:
- In order to seek truth, it is necessary once in the course of our life, to doubt, as far as possible, of all things.
- We ought also to consider as false all that is doubtful.
- We ought not meanwhile to make use of doubt in the conduct of life
- Why we may doubt of sensible things.
- Why we may also doubt of mathematical demonstrations.
- We cannot doubt of our existence while we doubt, and this is the first knowledge we acquire when we philosophize in order.
Descartes proceeded to strip away his knowledge base in order to determine the one indubitable fact, “Cogito, ergo sum”. From this absolute knowledge of his own existence, he set about deducing the existence of God through ontological argument. In our minds, the idea of God is one of an infinitely perfect Being An infinitely perfect being must have existence, otherwise it would not be infinitely perfect. In proving the existence of God, Descartes set the groundwork for determining that God created man.
He further postulated that God, being infinitely perfect and not a deceiver, could not have provided man with the deceptive powers of knowledge. Therefore, man’s mental faculties are determined to be trustworthy provided we separate what there is of clear and distinct in the knowledge from what is obscure and confused. Using this reasoning, man must discard all previous knowledge which is doubt-ridden, all sensory-based knowledge (as perceptions can be misleading), and all intellection. As a result, skepticism is removed and valid knowledge possible. Descartes primary purpose was the defense of human knowledge against the attacks of the skeptics. He was justified in excluding preconceived notions, presuppositions, and traditions in determining the limits of knowledge.
Descartes discarded the ability of the mind to know truth and the human abilities of contradiction and sufficient reason. In doing so, he made a solution to the problem impossible. As it relates to his theory of the existence of God, Descartes universal doubt refutes his own conclusion as to God’s existence. Descartes formed an idea of God as an infinitely good being. He would have had to discover this idea within his own mind.
According to his principle of universal doubt, he cannot simply know whether his conception of God is correct or incorrect. He would have, as a matter of his own principle, considered it as false until proven otherwise. Therefore, since the idea of God is in doubt, the trustworthiness of man’s reasoning must also be doubtful and Descartes cannot escape his own real doubt. Descartes uses a process of reasoning, a mathematical formulae, in attempting to demonstrate God’s existence.
If his reasoning is of demonstrably doubtful validity, how can Descartes demonstrate God’s existence? The validity of Descartes reasoning is supposed to flow as a consequence of the infinite perfection of God; and God’s infinite perfect is made certain through Descartes’ reasoning powers before he has even proven that these reasoning powers are valid and trustworthy. Descartes assumes the very thing beforehand which he intends to prove afterwards. (Begging the question). Descartes accepts the trustworthiness of his faculties in demonstrating the existence and infinite perfection of God, and that is illegitimate. A doubtfully valid faculty will produce a doubtfully valid argument which will, in turn, produce a doubtfully valid conclusion.
The entire argument for God’s existence is therefore nullified by a suspect reasoning process. Since he proves the reliability of his reason and process by means of God’s veracity, the proof of his reliability cannot be established beyond doubt. Thus, Descartes attempt to vindicate the validity of human knowledge failed, because, by rejecting the reliability of his own powers to discover and know truth, he made it impossible for himself to remove himself from his own universal doubt. Further, Descartes has marked inconsistencies in the manner in which he applies his procedure. He purports to reject everything in his pursuit of fundamental knowledge, even principles of contradiction and sufficient reason. In reality, he does not.
He assumes the truth of these principles and uses them repeatedly. “Cogito ergo sum” is based upon the validity of the principle of contradiction. This principle states that it is impossible for something to be and not be at the same time. Descartes becomes aware of his own existence by thinking or doubting. Why? Because he perceives that it is impossible to think and not think and to exist and not exist at the same time. If he were consistent and seriously doubted the principle of contradiction, he would have to agree that it is possible for an entity to think and not think, to exist and not exist at the same time.
Then, according to his own supposition, he could not be sure after all that the fact of his existence is certain. Only by granting the validity and truth of the principle of contradiction beforehand, can his existence be established as an objective fact. That is exactly what he does. The same line of reasoning applies to his proof of God’s existence and infinite perfection. Descartes rejection of the principle of contradiction invalidates his arguments because, as long as this principle is not established and accepted, he could never be sure whether it would be possible for God to exist and not exist at the same time.
Similarly, Descartes would have to remain doubtful as to whether God could be veracious and not veracious, deceiving and not deceiving unless the principle of contradiction was taken for granted before Descartes begins to prove God’s existence. Descartes does not accept this principle of contradiction throughout his reasoning. This is a glaring inconsistency in his arguments. Descartes further conducts his inquiry into the existence of God with the supposition that he doubts the principles of sufficiency and causality.
Unfortunately, he uses these principles before he has proven their validity. To wit: Descartes a posteriori argument for the existence of God. Descartes believes that God is an infinitely perfect being that could not have originated in our minds because an idea such as this would exceed the causality of the mind, as the mind is less perfect than the content of the idea itself. Consequently, the idea had to be produced by God himself otherwise there would be no sufficient reason for the presence of such an idea in the mind. Clearly, Descartes uses the principles of sufficient reason and causality in demonstrating the existence of God, even though he doubts their validity. Therefore, if he lets these principles stand as doubtful, his entire argument is nullified by doubt.
If he accepts them as valid prior to establishing their validity, he is acting in contrary to his fundamental doubt doctrine. In either case, he makes the existence of God impossible. Descartes could not prove God’s existence consistently as he could only do so through the use of a reasoning process which, according to his own principles, was essentially doubtful in its validity. The only thing he could ever be certain of was his own existence. This too, strictly speaking, he should have doubted, because he had doubted the principle of contradiction and the testimony of his own consciousness.
If Descartes had been consistent, he would have aligned with the skeptics because his universal doubt left him no other choice. Universal doubt, therefore, is a flawed course in pursuing an understanding of human knowledge and the existence of God. Complete doubt cannot lead to an understanding of human knowledge.