Ergo Proxy inside of themselves: the idea that there are two personalities inside a person and noted that René Descartes' phrase ""cogito, ergo sum"" was the inspiration for it. Satō stated that they originally did not want to explicitly express the concepts of Gnosticism in the anime. However, their personal beliefs ended up reflecting the ideas of Gnosticism and realized how well these terms fit and decided to use them. At first they intended to have Vincent as the leading protagonist and Re-l as a supporting character; however, as they fleshed out her character, she became a much stronger character and began
Cogito, ergo sum ("If I am mistaken, I am") (book XI, 26), and also anticipates modern refutations of the concept. Furthermore, in the "Enchiridion" Augustine attempts to refute skepticism by stating, "[B]y not positively affirming that they are alive, the skeptics ward off the appearance of error in themselves, yet they do make errors simply by showing themselves alive; one cannot err who is not alive. That we live is therefore not only true, but it is altogether certain as well" (Chapter 7 section 20). In 1640 correspondence, Descartes thanked two colleagues for drawing his attention to Augustine and notes similarity and difference.