Circle, Cartesian

Summary

In the Fourth Objections, Arnauld wrote:

I have one further worry, namely how the author avoids reasoning in a circle when he says that we are sure that what we clearly and distinctly perceive is true only because God exists. But we can be sure that God exists only because we clearly and distinctly perceive this. Hence, before we can be sure that God exists, we ought to be able to be sure that whatever we perceive clearly and evidently is true.

(AT VII 214, CSM II 150)

The circular argument or strategy identified here has come to be known as the Cartesian Circle. The Circle is constructed from two arcs. The first is that certainty of the truth of clear and distinct perceptions depends on God's attributes. In the Fourth Meditation, for example, Descartes uses the Third Meditation understanding of God to prove the rule that everything perceived with clarity and distinctness is true. The second arc is that certainty of God's existence depends on a proof from clear and distinct premises.

Descartes was not impressed by Arnauld's observation. He responded by saying that an adequate explanation was found in his Second Replies and added:

To begin with, we are sure that God exists because we attend to the arguments which prove this; but subsequently it is enough for us to remember that we perceived something clearly in order for us to be certain that it is true. This would not be sufficient if we did not know that God exists and is not a deceiver.

(AT VII 246, CSM II 171)

A vast literature has accumulated as the result of attempts to understand Descartes’ response and evaluate how successful it is. It is an attractive problem for scholars because it is, on the surface, so simple to formulate, and Descartes’ explicit treatments of the Circle are brief and cryptic. Moreover, the problem gains depth from its connection to central issues of doubt,method, clear and distinct perception, scientia, and the knowledge of God.