What role does Descartes Method of Doubt Play in the meditation?

The Method of Doubt employed by Descartes requires the individual to place everything he thinks he believes under a close scrutiny. Anything that cannot be proved beyond the slightest shadow of a doubt, Descartes rejects out of hand. Even so simple a perception as holding a piece of paper in your hand, Descartes finds too untrustworthy on which to base his system of philosophy. Can you truly be certain you aren't dreaming, he asks? Or, if not dreaming, what if you were mad, and while you were quite certain within your own mind that you held a piece of paper in your hand, the reality could be nothing of the sort. In this manner, Descartes systematically applies his doubts to every more basic layer of consciousness until all that he is left with is his conviction that if he can doubt, then there must be something that is doing that doubting. He must exist, if he can doubt, although it is unclear as of yet what form that existence may take.