Begging the Question is a fallacy that occurs when one's argument goes in circles. the Cartesian Circle is an example of Begging the Question. Louis E. Loeb writes:
"Descartes writes in the second paragraph of the Third Meditation: “So I now seem to be able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true ” (AT VII 35: CSM II 24)... Descartes concludes, on the ground that God is no deceiver, that “if . . . I restrain my will so that it extends to what the intellect clearly and distinctly reveals, and no further, then it is quite impossible for me to go wrong” (AT VII 62: CSM II 43)."
http://cco.cambridge.org/extract?id=ccol0521366232_CCOL0521366232A009
Descartes needs both God and clear and distinct ideas in order to prove the existence of God, which runs in circles.
