This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Before his conversion, Augustine spent roughly a decade as an adherent of Manichaeism, a religion that explained the presence of evil in the world by positing two co-eternal principles locked in cosmic combat, one wholly good and one wholly evil, with the visible world and the human soul caught in the crossfire between them. Manichaean doctrine treated evil as a substance, a positive force with its own nature and its own kind of being, invading and contaminating the light trapped within matter and within the human body. This picture had obvious appeal to someone troubled by the problem of moral failure, since it located the source of wrongdoing outside the self, in an alien substance battling for control of the soul, rather than in the agent's own will.
Augustine's mature philosophical response, worked out most fully after his conversion, rejects this picture at its foundation by denying that evil has any substantial existence at all. His governing claim is that everything that has being is good insofar as it has been created by God, since God, being good, could create nothing that was not in some degree good. Evil, on this account, is not a rival substance or a competing principle but a privation or corruption of goodness, a falling away from the fullness of being that a thing ought to have rather than the presence of some new and hostile ingredient. A wound is not a substance added to healthy flesh but an absence of the wholeness flesh should have; a lie is not a new kind of truth but a truth that has gone missing. Evil is parasitic on good in the sense that it can only ever be a defect in something that is, at bottom, good by virtue of existing at all.
This move does real philosophical work beyond simply refuting a rival sect. It allows Augustine to preserve the goodness and omnipotence of a single creator God without either blaming God for evil or admitting a second, independent source of it into the universe. Since evil is not a thing God made but the absence of a good that something else failed to retain, God's creation remains wholly good in its origin even though corruption has since entered particular created things. At the same time, the theory relocates responsibility for wrongdoing back onto the agent, since if there is no external evil substance forcing itself upon the will, then moral failure must be explained by Augustine's account of sin as an unjust volition, a disordered choice of the will itself rather than the victory of an invading force. This is precisely the move that Manichaeism, with its cosmic battle between substances, had made unnecessary and even incoherent, since on that view the soul is more battlefield than agent.
The privation theory therefore does more than answer an abstract metaphysical question about the nature of evil. It dismantles, term by term, the explanatory apparatus that had made Manichaeism attractive to Augustine as a young man, replacing a drama of contending substances with an account in which everything that exists tends toward goodness by the mere fact of its existence, and everything that goes wrong does so not because darkness has invaded the light but because a good will has turned away from the good it was made to seek. The argument's economy is part of its force, rather than needing to explain why an evil principle exists at all, Augustine needs only to explain the will's own capacity to fall short, a far smaller and more tractable philosophical debt.