Descartes opens Meditation I with his persona, the meditator, reflecting on the project to be undertaken. Descartes writes:

And with this, the project has begun. Descartes' meditator quickly begins by rejecting the commonsense epistemological principles on which everything he formerly believed rested, and quickly sets about putting the world back together again. Of course, one of the central projects undertaken in this connection must be the replacement of the epistemological principles rejected with new, more trustworthy principles. Just as Descartes' meditator undermined his former beliefs by undermining the epistemology on which they were based, he will rebuild his world by rebuilding its epistemology. New epistemological principles thus seem to be the very “first foundations” on which he will build something “firm and lasting in the sciences.” But an obvious question to raise about this, the opening sentence of the Meditations, and about the project that follows out of it, is why? Why does Descartes believe it necessary even once in life to rebuild all of our beliefs in the way he suggests? Why does Descartes feel called to such an epistemological project?