In response to Pelagius, Augustine adopted a theological system that included not only original sin (which Pelagius denied), but also predestination, limited atonement, and irresistible grace. Critics maintain that part of Augustine's philosophy might have stemmed from his expertise in Greek philosophy, particularly Platonism and Manichaeism, which maintained a very high view of a man's spirit and very low view of a man's body. Against the Pelagian notion that man can do everything right, he taught the notion that man can do nothing right. Thus, he reasoned, man cannot even accept the offer of salvation — it must be God who chooses for himself individuals to bring to salvation.