The Cartesian Circle

The Cartesian Circle

1. Why circular reasoning is a logical fallacy

Suppose two arguments, A and B. The conclusion of A is a premise for B, and the conclusion for argument B is the premise for argument A. Written out, it would look something like this: 

Argument A: 

1. If M, then P

2. M

3. Therefore P

Argument B: 

1. If P, then M

2. P

3. Therefore M

The weakness in these two arguments is that premise number 2 in both arguments are conclusions of the other argument (assuming that there is no other method in which arguments A or B is proved). This is named circular reasoning, because there is no way to verify the truth of either statement. 

In order to affirm the truth of argument A, then both premises 1 and 2 must be true. However, to prove the truth of premise 2, argument A (assuming premise 1 is proven with another method), we must move to argument B (which proves the truth of premise 2 in argument A). But to prove the truth of argument B (in order to confirm the truth of premise 2 in argument A), we must prove the truth of premise 2, argument B. In order to prove premise 2, argument B, we must move back again to argument A, whose conclusion asserts that premise 2, argument B is true. But to prove argument A is true, we must…. One can see, how, if there is no other way to guarantee the truths of the premises, there is no way to prove both arguments true, as this loop would go on infinitely. Since there is no way to guarantee the truth of either statement, then this is a case of logical fallacy, as the argument (the premises and logic) is not supported enough to arrive at the conclusion. 

2. The Cartesian Circle—A Logical Fallacy:

Proof of God: 

1. I have a clear and distinct idea of a perfect being

2. A clear and distinct perception must be true

3. Therefore premise 1. is true

4. Existence is part of being perfect (something that exists is more perfect than something that is not)

5. Therefore a perfect being (God) must exist. 

Guarantee of clear and distinct idea:

1. God would not allow an evil demon to deceive me and thus guarantees the truth of clear and distinct perceptions.

2. Therefore I can be certain of things that I perceive distinctly and clearly. 

Descartes, in his Proof of God, uses his ‘clear and distinct idea’ to justify God’s existence. However, he then uses God to guarantee the truth of his clear and distinct ideas and perceptions, which was the premise/basis of his proof of God. The conclusion of his proof of God is used to justify the guarantee of a clear and distinct idea, which is then used to justify the truth of God. This is a case of circular reasoning, as under the pretenses that Descartes gives, the circle would go on forever without any way to prove either statement correct. 

3. Leading to later philosophers 

Descartes’ reasoning marks one of the first attempts to resolve doubt and gain true knowledge on the world. His attempt to use pure reason to resolve his own radical skepticism seemed to fail. But for Descartes, this was the necessity he had to get past in order to justify science and perception at all. He had to get past his skepticism with reason, yet reason was the very thing he put to doubt, requiring him to use God as an external factor to guarantee his beliefs. His attempt, however, ultimately resulted in a case of circular reasoning and fallacy. 

This radical doubt and its weakness influenced some later philosophers (other rationalists continued on the path of pure reason as well) to take a completely different route, avoiding reason. They believed in using observation and experience to obtain true knowledge, questioning the extent to which pure reason can provide knowledge without any empirical evidence. But observation and experience also required philosophical grounding, and questions were raised of whether we can perceive things in themselves, or merely mental representations of actual things. These questions of the senses in empiricism later lead to various ‘factions’ inside empiricism: the indirect realism of John Locke, the idealism of George Berkeley, and the direct realism of Thomas Reid.