The Cartesian Circle and Two Forms of Scepticism

I use Descartes's circle to facilitate our understanding of two types of scepticism and the proper attitude to them. Descartes's text is especially apt for this purpose, because a case can be made for attributing to him both types. Although I touch on the interpretative question, that is not my main aim. My contention is that one brand--whether or not it is the one that Descartes favoured--should be taken very seriously and Descartes's failure to respond to it noncircularly cannot be met with equanimity.