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 itself is good and pleasant (...) and if one who sees is conscious that he sees, one who hears that he hears, one who walks that he walks and similarly for all the other human activities there is a faculty that is conscious of their exercise, so that whenever we perceive, we are conscious that we perceive, and whenever we think, we are conscious that we think, and to be conscious that we are perceiving or thinking is to be conscious that we exist... ("Nicomachean Ethics", 1170a25 ff.) Augustine of Hippo in "De Civitate Dei" writes "Si […] fallor, sum"