The aim of this study is to reconstruct the theological controversy between Augustine of Hippo - who received the title of doctor gratiae, due to the fact that he acted as protector of grace against its enemies- and Pelagius, a British monk who has a reputation as spiritual teacher and theologian of great culture. This study, after highlighting the essential elements of Pelagianism, will analyse some of the most relevant themes of the doctrinaire conflict between Augustine and Pelagius, such as the concepts of Free Will, Mercy, original sin and grace.


Keywords: Augustine of Hippo; Mercy; Pelagius; Pelagianism.