According to many critics, Descartes argued in a circle when he presumed to base the certainty (and thus knowledge) of propositions that fulfill his epistemic criterion of being “clearly and distinctly perceived” on the demonstration that God exists and is not a deceiver. But his critics say, that demonstration, as he presented it, presupposed the validity of the same epistemic criterion. I critically examine two major strategies to dispel the appearance of circularity, two ways of interpreting Descartes’ argument.My approach shares (...) with the second strategy the contention that Descartes did adopt the principle that “whatever is clearly and distinctly perceived to be true is true,” prior to his consideration of the God question. Moreover, his demonstration of God’s existence and veracity made use of the principle. But my claim is that the knowledge of God’s existence and veracity is not used to validate the principle of clear and distinct perception (that would be unnecessary). It is used rather to defeat the sceptic’s argument that we cannot have any knowledge of the external, physical world. I proceed to present and explain Descartes’ argument centered around the thesis, “I cannot be certain that (r) any of my representational ideas of the external world are veridical, unless I am certain that (q), God exists and is not a deceiver.” That is, I prove why, for Descartes, (q) is necessary for (r). My discussion exposes some new facets to the principle of clear and distinct perception and reveals the fact that some familiar Cartesian distinctions that were not thought to be relevant to the problem of the Cartesian Circle are crucial to the solution of that problem. (shrink)