Descartes’ Circular Reasoning?

Ever since Descartes published his book Meditations he has been accused of committing a fallacy of circular reasoning with his argument that God is the guarantor of the truth of our belief in an external world. Descartes’ argument has ever since been derided as the “Cartesian Circle.” The problem is that the so-called “Cartesian Circle” is a misrepresentation of what Descartes’ actually arguement.

The accusation against Descartes is that he asserts that the existence of God verifies that clear and distinct ideas must be true. So those who argue the “Cartesian Circle” position are claiming that Descartes is arguing the following:

    1. 1. I have a clear and distinct idea of God as a perfect being.
    1. 2. God, a perfect being, is not a deceiver and would not allow me to be mistaken about my clear and distinct ideas.
    1. 3. Therefore, I can be certain of the truth of my clear and distinct ideas.

As the Encyclopedia Britannica states it (I think a reasonable summation of the standard interpretation of the Cartesian Circle):

But Descartes cannot know that this proof does not contain an error unless he assumes that his clear and distinct perception of the steps of his reasoning guarantees that the proof is correct. Thus the criterion of clear and distinct perception depends on the assumption that God exists, which in turn depends on the criterion of clear and distinct perception.


This is a valid assessment of the argument stated above.The “Cartesian Circle” claim is that Descartes asserts premise 1 but that premise depends on his conclusion, 3; a circular argument.

The question though is whether that is an accurate portrayal of Descartes’ actual argument. Garret Thomson in Bacon to Kant argues that it is not. The key to understanding Descartes’ argument, he says, is to discern the difference between particular experiences and the whole of experience. Understanding Descartes’ argument correctly dissolved the objection that his argument is circular.

Crucial to correctly understanding Descartes is to realize that he does not begin his argument by asserting God. In fact, God is an afterthought for Descartes. He trots out God only toward the end, and only in support of a secondary argument. Descartes foundational principle is the proposition “ideas that are clear and distinct must be true.” Everything else follows from that. Any idea that can be said to be clear and distinct then must be accepted as true. The proposition that clear and distinct ideas must be true is true (or false) independent of God and it is significant that Descartes establishes the proposition before he turns to the idea of God.

Thomson portrays Descartes’s reasoning in this way:

    1. 1. Ideas that are clear and distinct must be true.
    1. 2. I have a clear and distinct idea of God.
    1. 3. Therefore, God must exist.
    1. 4. Since my idea of God includes his perfection, God is trustworthy.
    1. 5. Therefore, I cannot be deceived about the existence of the external world because God would not allow me to be deceived.

It is important to accept that, as Descartes constructs his argument, premise 1 does not depend on premise 3. The “Cartesian Circle” incorrectly flips the two premeses. God is a clear and distinct idea and thus God’s existence cannot be doubted, just like our own existence and every other clear and distinct idea cannot be doubted.

The existence of God does not support the proposition “ideas that are clear and distinct must be true.” Descartes uses God’s existence as a prop to guarantee that our sensory perception as a whole is trustworthy. As Thomson puts it on p. 35, “God is introduced to meet our general systematic doubts.” We can, as Descartes points out, doubt each of our perceptions and beliefs because we know our senses can trick us. We could be deceived by an evil demon into believing all kinds of falsehoods. But God ensures that we are not deceived because God is not a deceiver. The God prop is used to answer the doubt that we are deceived by an evil demon into believing wholesale falsehoods about the world.

Descartes is not saying that he cannot be mistaken about particular propositions such as “that tree looks safe to climb” because he knows his will can overreach and lead him to error. But because he knows he is a mind who can use the power of reason and because he knows God is not an evil deceiver, then knowledge from experience is possible. Thus, if he can reason correctly (his four rules of scientific method) then his mind is incapable of error because he can reason from clear and distinct ideas to truth. We still must be on guard to not make mistakes in our sensory perceptions of the world

Descartes’s argument can be questioned on several of its premises, but it is not circular reasoning.

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