By “post-medieval Augustinianism” I shall mean characteristically Augustinian concepts, questions, arguments, responses, and ways of thinking that are prominent in various modern philosophers, whether or not those philosophers ever acknowledge the Augustinian provenance of these aspects of their own thinking. On this way of understanding “Augustinianism ” Descartes is perhaps the most Augustinian of modern philosophers, even though Descartes himself declined to acknowledge that there was any significant affinity between his own thought and that of Augustine (let alone that Augustine had actually influenced his thinking!). Both because Descartes was so profoundly Augustinian in his ways of thinking and because he inaugurated the “post-medieval” period in Western philosophy, I shall begin with him.