 The main inspiration for Augustine’s doctrine of grace is, of course, Paul (even though remarks on human weakness and divine help are not absent from the ancient philosophical tradition and especially from Platonism which had had a strong religious side from the beginning; Augustine claims that with such utterances the Platonists inadvertently “confess” grace, cf. De civitate dei 10.29; 22.22). The radical view that the gifts of grace include not only external good works and the internal volitional disposition that allows us to perform them but even the very first beginnings of faith—in later technical terminology: that grace is not “cooperative” but radically “prevenient”—is however his own, and it took several years to take shape in his thought. There is some debate on the stages of this development (for diverging reconstructions, see Karfíková 2012; Cary 2008a; Drecoll 2004–2010; Drecoll 1999; emphasis on the shifts in Augustine’s thinking: Lettieri 2001; Flasch 1995; emphasis on continuity: C. Harrison 2006), but it is generally agreed that Augustine’s doctrine of grace reached its mature form c. 395–397 with Ad Simplicianum 1.2, after several years of intense reading and exegesis of Paul, and gained higher profile during the Pelagian controversy after 412. Augustine emphasizes the necessity of grace for both intellectual understanding and moral purification already in his earliest works (cf. esp. Soliloquia 1.2–6), but seems to have been concerned to leave room for human initiative at least with respect to faith and will (which would be in line with his concern, prominent throughout the 390s, to safeguard human responsibility against Manichean fatalism). In his early exegesis of Paul, he explains God’s apparently gratuitous election of Jacob and rejection of Esau (Romans 9:10–13) with God’s foreknowledge of Jacob’s faith and Esau’s infidelity (De diversis quaestionibus 68.5; Expositio quarundam propositionum ex epistula apostoli ad Romanos 60), a “synergistic” reading that relies on the assumption that salvation results from the cooperation of divine grace and human initiative and that had been standard in early Christianity since Origen. This explanation is explicitly rejected in Ad Simplicianum (1.2.5–6; 8; 11). In this pivotal text, Augustine, true to his program of “faith seeking understanding”,  attempts an exegesis of Romans 9:9–29 that satisfies the philosophical requirements of God’s justice and benevolence while taking seriously the Pauline point that God’s election is entirely gratuitous and not occasioned by any human merit. The guiding intention of Romans 9, Augustine now says, is to preclude vainglory and pride (ib. 1.2.2) rather than to safeguard human responsibility (as had been his view in Expositio quarundam propositionum ex epistula apostoli ad Romanos 13–18). Augustine rehearses all possible reasons for God’s election of Jacob—his good works, his good will, his faith and God’s foreknowledge of each—and discounts them all as amounting to an election from merit rather than from grace. Starting from the primordial willingness to heed God’s call to faith, then, everything that is good in Jacob must be considered a gift of divine grace. Free will has nothing to do with the reception of that gift because nobody can will to receive a divine call to faith nor to respond positively to it so as to act accordingly and perform good works out of love (Ad Simplicianum 1.2.21; for the Stoically-inspired theory of agency behind this see  7.4 Will and Freedom).  While gratuitous election is, apart from being consoling, comparatively easily squared with the axioms of divine benevolence, justice and omnipotence, its corollary, the equally gratuitous reprobation and damnation of Esau, is a serious philosophical problem (ib. 1.2.8). If it is not to violate the principle of God’s justice, it obliges us to assume some kind of evil in Esau, which is however excluded by Paul’s explicit statement to the contrary (Romans 9:11). Augustine’s solution is his doctrine of original sin. Both Jacob and Esau have inherited Adam’s guilt that his sin has spread over all humankind—a debt that God remits for Jacob but exacts from Esau for reasons that, Augustine admits, necessarily elude human understanding but are certainly just. Since the Fall, humankind is nothing but a “lump of sin” that God might justly have damned as a whole but from which he has chosen to save some individuals and to transform them into “vessels of mercy” (ib. 1.2.16, cf. Romans 9:23). The notion of original sin was not invented by Augustine but had a tradition in African Christianity, especially in Tertullian.  The view that original sin is a personally imputable guilt that justifies eternal damnation is, however, new with Ad Simplicianum and follows with logical necessity from the exegetical and philosophical claims made there about divine grace and election (Flasch 1995; contrast De libero arbitrio 3.52–55). The theory of Ad Simplicianum is illustrated, with great philosophical acumen and psychological plausibility, in the Confessiones (especially bk. 8) and remains in place during the Pelagian controversy till the end of Augustine’s life. Curiously, however, there are passages even in his anti-Pelagian work that seem aimed at safeguarding freedom of choice and, accordingly, admit of a “synergistic” reading (De spiritu et littera 60; Cary 2008a: 82–86 and, for a different interpretation, Drecoll 2004–2010: 207–208). After 412, pressed by his Pelagian opponents, Augustine paid increasing attention to the mechanics of the transmission of original sin. The result was a quasi-biological theory that associated original sin closely with sexual concupiscence (see  9. Gender, Women and Sexuality).