This ontological argument originated in the work of St. Anselm, the medieval Scholastic philosopher and theologian. While Descartes had already claimed to have confirmed God's existence through previous arguments, this one allows him to put to rest any discontent he might have had with his "distinct and clear" criteria for truth. With a confirmed existence of God, all doubt that what one previously thought was real and not a dream can be removed. Having made this realization, Descartes asserts that without this sure knowledge in the existence of a supreme and perfect being, assurance of any truth is impossible:Thus I plainly see that the certainty and truth of all my knowledge derives from one thing: my thought of the true God. Before I knew Him, I couldn't know anything else perfectly. But now I can plainly and certainly know innumerable things, not only about God and other mental beings, but also about the nature of physical objects, insofar as it is the subject-matter of pure mathematics.