The Manichees had the best answer going to the question that outranked all others in fourth-century Roman Africa: if a single good God made everything, where did evil come from? Two eternal powers, they held, light and dark, at war across the cosmos and inside every person. Evil was a substance. It had invaded the soul, and what a man did wrong was not, at bottom, his. The churches answered the same question poorly, and a rhetoric teacher from Thagaste judged the Manichaean account the only one on offer that survived examination; he stayed inside it for nine years as an auditor of the sect.
What broke it, in the end, was a conversation that disappointed him. His doubts had settled on astronomy — the Manichaean stories about the sun, moon and stars did not match what anyone could calculate — and he was told to wait for Faustus, the movement's most celebrated teacher. Faustus arrived in Carthage, spoke beautifully, and knew no more than Augustine did. Augustine still did not leave, having nowhere to go.
The exit came in Milan. He took a publicly salaried chair of rhetoric there in 384, heard Ambrose read scripture as allegory rather than as literal report, and in 386 read Latin translations of Plotinus and Porphyry. Those books handed him the move that dismantled the problem entirely: evil is not a thing but a privation, a good thing lacking what it ought to have, the way blindness is an eye missing sight rather than a substance of its own. Nothing evil was ever created, because evil was never a creature at all.
The solution came with a bill, and paying it is what made him a philosopher rather than a convert. If evil is not foreign matter lodged in a man, the disorder is his own willing — and Augustine spent forty years on what willing then turns out to be. He found it divided against itself. A man commands his hand and the hand obeys; he commands his own will and is refused. Confessions, written around 396 to 400 by a bishop about a man he had stopped being, reports that discovery, turning the first person into an instrument for the argument that a person is opaque to himself. In City of God he pressed the same instrument further, observing that anyone deceived must exist in order to be deceived, twelve centuries before Descartes built a system on the point.
He argued the rest in public, ordained at Hippo in 391 apparently against his will and bishop by 396, leaving some three hundred letters and six hundred sermons. When Rome fell to the Visigoths in 410 and pagans blamed the Christians, he began City of God: twenty-two books, finished in 426, dividing history into two cities and detaching the fate of the faith from the fate of any empire. The West took its first philosophy of history from it.
The bitterest fight was also the last: Pelagius taught that God commands nothing a person cannot perform; Augustine answered that the will is bound and only grace releases it, and won — Carthage condemned Pelagius in 418 — while Julian of Aeclanum went on attacking him until his death. His hardest positions belong to those years: predestination, and the fate of infants who died unbaptized. Scholars still disagree over whether the grace he described leaves any room to choose.
His authority went essentially unchallenged in the West until the nineteenth century, and is now contested hard from several directions, though the question he made unavoidable is not. He died on 28 August 430 with Vandals besieging Hippo. Three years earlier he had gone back over ninety-three of his own books and catalogued their errors himself.