Influence of the dualist ‘Encratite’ tradition helps account for the pessimistic colouring of Augustine’s view of human nature, but this is far from being the whole story, in which a turning point was his attempt to explain what it could mean to say that God hated Esau. The sacred books which both Augustine and Pelagius accepted without question could bear either of their probably honest interpretations of grace. Even modern scholars can react strongly in opposite directions to this fifth-century controversy, on a spectrum from barely concealed dislike of Augustine’s idea of grace to apparently heartfelt eloquence in presenting it. While twenty-first-century society is comfortable with pluralism, at least on these topics, fifth-century Christianity was not. Contradictory certainties must have generated both uncertainty and unease among those not committed to either side.