The Cartesian Circle and Its Critics

Among the sharpest objections raised against Descartes's Meditations, both by his own contemporaries and by later commentators, is the charge that his argument moves in a vicious circle — an objection that has come to be known as the "Cartesian Circle." The difficulty was first stated with precision by Antoine Arnauld, the Jansenist theologian and logician, in the Fourth Set of Objections (1641), and independently raised in similar terms shortly afterward by Marin Mersenne in correspondence and by other early readers of the Meditations. The problem arises from the structure of Descartes's overall argument: in the Third Meditation, Descartes seeks to establish the existence of a benevolent, non-deceiving God partly in order to guarantee that whatever he perceives "clearly and distinctly" is true — since, absent such a guarantee, even mathematical truths that seem utterly certain to Descartes might, under the hypothesis of the evil genius, still be false. Yet the very proofs of God's existence that Descartes offers in the Third and Fifth Meditations themselves proceed by identifying premises that Descartes finds clear and distinct (for instance, that the idea of an infinite, perfect being could not have been caused by a finite, imperfect thinker, or that existence belongs necessarily to the concept of a supremely perfect being). Arnauld's objection is that Descartes appears to use clear and distinct perception to prove God's existence, and then to use God's existence (as guarantor of non-deception) to certify that clear and distinct perception is reliable — a circle in which each of the two conclusions depends on the other already being established.