Ever since Arnauld and others first pointed it out in their objections to Descartes' Meditations, philosophers have concerned themselves with what appears to be a vicious circle: that the principle of clarity and distinctness which is employed to validate God's existence is itself in need of a guarantee which only God's existence can provide. In general, contemporary commentators proposing solutions to this problem can be divided into three camps: first, there are those who see reason as autonomous for Descartes and (...) the principle of clarity and distinctness as needing no guarantee. By 'autonomy of reason' I mean that the faculty by which the Cogito and other of Descartes' first principles are perceived is not in need of any verification of its inability to err. Second, there are those who see reason as only partially autonomous for Descartes with that part validating the proof of God's existence which in turn validates that aspect of reason which is not autonomous. Third, there are those who see reason as non-autonomous and who argue for distinctions in the concepts of certainty and doubt in order to avoid the circle. ;In this dissertation I present the problem by drawing directly from the Meditations and the Objections and Replies and I outline the strategy I will employ in dealing with the problem. I proceed to discuss in turn each of the aforementioned three positions, the arguments offered by proponents of each, and the criticism of each, both my own and those found in the literature of the problem. Taking the third position, the non-autonomy of reason, as my starting point, I then present my own interpretation of Descartes' strategy which, I argue, succeeds in circumventing the problem of circular reasoning and in overcoming the objections raised against others. (shrink)