On Nature and Grace (De Natura et Gratia)

On Nature and Grace, De Natura et Gratia, written by Augustine of Hippo around 415, is Augustine's own polemical treatise against Pelagius, arguing that human nature, wounded by original sin, cannot achieve righteousness without divine grace, a position that became foundational to later Western Christian, and especially Catholic and Reformation, theology of grace and free will. Its strength is that it is the primary text itself, from the controversy's leading opponent of Pelagianism, so a claim about what Augustine actually argued, rather than how later tradition summarized him, can be checked against his own words. Its limit is that it is one side of a live theological argument, written specifically to refute Pelagius's own treatise On Nature, which does not survive complete and is known largely through Augustine's own quotations of it, so a claim needing a fair account of the Pelagian position itself is working from a source that had every reason to characterize its opponent unfavorably.