Cartesian circle

The Cartesian circle is a potential mistake in reasoning attributed to René Descartes.

Descartes argues – for example, in the third of his Meditations on First Philosophy – that whatever one clearly and distinctly perceives is true: "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) He goes on in the same Meditation to argue for the existence of a benevolent God, in order to defeat his skeptical argument in the first Meditation from the possibility that God be a deceiver. He then says that without his knowledge of God's existence, none of his knowledge could be certain. The argument takes this form: (1) Descartes' proof of the reliability of clear and distinct perceptions takes as a premise God's existence as a non-deceiver. (2) Descartes' proofs of God's existence presuppose the reliability of clear and distinct perceptions.