To which I reply:
"Now with the exception of the holy Virgin Mary in regard to whom, out of respect for the Lord, I do not propose to have a single question raised on the subject of sin -- after all, how do we know what greater degree of grace for a complete victory over sin was conferred on her who merited to conceive and bring forth Him who all admit was without sin -- to repeat then: with the exception of this Virgin, if we could bring together into one place all those holy men and women, while they lived here, and ask them whether they were without sin, what are we to suppose that they would have replied?" (On Nature and Grace, or De natura et gratia, Migne PL 44:267)
a) In this quotation, Augustine is refusing (at the time) to address the question of whether Mary had sin. He does not assert that she was sinless.
b) Augustine is saying that there is one (Jesus Christ) who certainly had no sin.
c) Augustine is addressing the issue of actual sin, not original sin.
Moreover, just a short time before writing "On Nature and Grace," Augustine wrote "On Merits and Forgiveness of Sins," in which he spoke more clearly:
This being the case, ever since the time when by one man sin thus entered into this world and death by sin, and so it passed through to all men, up to the end of this carnal generation and perishing world, the children of which beget and are begotten, there never has existed, nor ever will exist, a human being of whom, placed in this life of ours, it could be said that he had no sin at all, with the exception of the one Mediator, who reconciles us to our Maker through the forgiveness of sins.NPNF1: Vol. V, On Merits and Forgiveness of Sins, and on the Baptism of Infants, Book II, Chapter 47.
Let us hold fast, then, the confession of this faith, without filtering or failure. One alone is there who was born without sin, in the likeness of sinful flesh, who lived without sin amid the sins of others, and who died without sin on account of our sins. “Let us turn neither to the right hand nor to the left.” For to turn to the right hand is to deceive oneself, by saying that we are without sin; and to turn to the left is to surrender oneself to one’s sins with a sort of impunity, in I know not how perverse and depraved a recklessness. “God indeed knoweth the ways on the right hand,” even He who alone is without sin, and is able to blot out our sins; “but the ways on the left hand are perverse,” in friendship with sins.NPNF1: Vol. V, On Merits and Forgiveness of Sins, and on the Baptism of Infants, Book II, Chapter 57 [XXXV].
Likewise, at the very end of his life, in his "Unfinished Work in Answer to Julian," Augustine wrote something similar:
Augustine (354-430 AD): See, here is Ambrose; see what he says about what you are attacking. He says, “He could not alone be righteous, since the whole human race went astray, if it were not that, because he was born of a virgin, he was not held by the law of the guilty race.” Listen further; listen and stop the impudent tongue of your effrontery by shedding tears: “For intercourse with a man did not open the gates of the Virgin’s womb; rather, the Holy Spirit poured spotless seed into that inviolable womb. For among those born of a woman the holy Lord Jesus was absolutely the only one who did not experience the contagion of earthly corruption because of the new manner of his immaculate birth; rather, he shrugged it off by his celestial majesty.” John E. Rotelle, O.S.A., ed., Works of Saint Augustine, Answer to the Pelagians III, Unfinished Work in Answer to Julian, Book I:66, Part 1, Vol. 25, trans. Roland J. Teske, S.J. (Hyde Park: New City Press, 1999), p. 91.
And if you will not accord weight to the testimony of an unfinished work, consider what Augustine wrote in his letters.
First, his letter to Jerome that was the same year as his publication of "On Nature and Grace":
Therefore it is true that in the sight of God “shall no man living be justified,” and yet that “the just shall live by his faith.” On the one hand, “the saints are clothed with righteousness,” one more, another less; on the other hand, no one lives here wholly without sin—one sins more, another less, and the best is the man who sins least.NPNF1: Vol. I, Letters of St. Augustin, Letter 167 - To Jerome, Chapter 3, §13.
Second, his letter to Optatus about two years later:
For, if no soul is propagated from another, while all souls are enclosed in flesh descended from sinful flesh, how much less credible is it that His soul could have come by propagation from a sinful woman, whereas his flesh came from a virgin and was not conceived in lust, that He might be ‘in the likeness of sinful flesh,’ not in sinful flesh!See FC, Vol. 30, Saint Augustine Letters 165-203, Letter 190, to Optatus (New York: Fathers of the Church, Inc., 1955), p. 287.
And then again to Optatus five years after writing "On Nature and Grace":
In the advice and admonition he gives that I rather apply my effort to stamping out this deadly heresy from the Churches, he refers to that same Pelagian heresy which I urge you, my brother, with all my strength, to avoid with the utmost care, whenever you either think or argue about the origin of souls, so that the belief may not steal upon you that any soul at all, save that of the unique Mediator, was free from inheritance of Adam, that original sin under which we are bound when we are begotten but from which we are freed by our second birth.FC, Vol. 30, Saint Augustine Letters 165-203, Letter 202A, To Optatus (New York: Fathers of the Church, Inc., 1955), p. 420.
And while my correspondent simply asserts that Augustine did not come up with the content quoted in "On Nature and Grace," we can prove that Augustine -- in holding to the universality of original sin to those born from sexual intercourse -- was following his teacher Ambrose.
Ambrose (c. 339-97) commenting on Luke 1:35:
For wholly alone of those born of woman was our Holy Lord Jesus, Who by the strangeness of His undefiled Birth has not suffered the pollutions of earthly corruption, but dispelled them by heavenly majesty.Saint Ambrose of Milan, Exposition of the Holy Gospel according to Saint Luke, trans. Theodosia Tomkinson (Etna: Center for Traditionalist Orthodox Studies, 1998), Book II, §56, p. 59.
Ambrose (c. 339-97): No Conception is without iniquity, since there are no parents who have not fallen. (Nec conceptus iniquitatis exsors est, quoniam et parentes non carent lapsu. ) Prophetae David ad Theodosium Augustum, Caput XI, PL 14:873; for translation, see I. D. E. Thomas, The Golden Treasury of Patristic Quotations (Oklahoma City: Hearthstone Publishing, 1996), p. 258.
Ambrose (c. 339-97):
So, then, no one is without sin except God alone, for no one is without sin except God. Also, no one forgives sins except God alone, for it is also written: “Who can forgive sins but God alone?” And one cannot be the Creator of all except he be not a creature, and he who is not a creature is without doubt God; for it is written: “They worshipped the creature rather than the Creator, Who is God blessed for ever.” God also does not worship, but is worshipped, for it is written: “Thou shalt worship the Lord thy God, and Him only shall thou serve.”NPNF2: Vol. X, On the Holy Spirit, Book III, Chapter 18, §133.
Ambrose (c. 339-97):
Let us therefore consider whether the Holy Spirit have any of these marks which may bear witness to His Godhead. And first let us treat of the point that none is without sin except God alone, and demand that they prove that the Holy Spirit has sin.NPNF2: Vol. X, On the Holy Spirit, Book III, Chapter 18, §134.
And we don't have to speculate whether Augustine was consciously agreeing with Ambrose:
Augustine (354-430 AD):
Hilary says that all flesh comes from sin apart from the flesh of the one who came without sin in the likeness of sinful flesh. He says that the one who cried out, I was conceived in iniquities (Ps 51:7), “was born from a sinful origin and under the law of sin. Saint Ambrose says that “the little ones who have been baptized are changed from their wickedness back to the original state of their nature.” He says that “by reason of his immaculate birth the Holy Lord Jesus alone of those born of a woman experienced no infection from earthly corruption." He says that we all die in Adam, because through one man sin entered the world (Rom 5:12) and his sin is the death of all. He says that in his wound “the whole human race would have died, if that Samaritan had not come down and healed his grave wounds.” He says that Adam existed and all existed in him, that Adam perished and all perished in him. He says that we are stained with infection before we were born and that a human being is not conceived free of iniquity, because, as he says, we are “conceived in the sin of our parents and we are born in their transgressions. Birth itself has its own infections, and nature itself does not have only one infection.” He says that the devil is a money lender to whom sinful Eve “put the whole human race in debt with succeeding generations subject to usury.” He says that Eve was deceived by the devil “in order to trip up her husband and place their descendants in debt.” He says that Adam was so wounded by the bite of the serpent “that we all limp because of that wound.” He says that through the union of the bodies of the man and the woman no one is immune from transgression, but that “the one who is immune from transgression,” that is, Christ the Lord, “is also immune from that manner of conception.”See John E. Rotelle, O.S.A., ed., Works of Saint Augustine, Answer to the Pelagians III, Answer to Julian, Book I:7, 32, Part 1, Vol. 24, trans. Roland J. Teske, S.J. (Hyde Park: New City Press, 1998), pp. 290-291.
Augustine (354-430 AD):
Say to this man [i.e., Ambrose], if you dare, that he makes the devil the creator of human beings who are born from the union of both sexes. He, after all, exempted Christ alone from the bonds of the guilty race, because he was born of a virgin. All the others coming after Adam are born under the debt of sin, the sin which the devil, of course, planted in them. Refute this man for condemning marriage, for he says that only the son of the virgin was born without sin. Charge this man with denying the attainment of virtue, since he says that vices are implanted in the human race at the very beginning of conception.See John E. Rotelle, O.S.A., ed., Works of Saint Augustine, Answer to the Pelagians III, Answer to Julian, Book II:2, 4, Part 1, Vol. 24, trans. Roland J. Teske, S.J. (Hyde Park: New City Press, 1998), p. 306.
Augustine (354-430 AD):
Moreover, when expounding the Gospel according to Luke, he [i.e. Ambrose] says: “It was no cohabitation with a husband which opened the secrets of the Virgin’s womb; rather was it the Holy Ghost which infused immaculate seed into her unviolated womb. For the Lord Jesus alone of those who are born of woman is holy, inasmuch as He experienced not the contact of earthly corruption, by reason of the novelty of His immaculate birth; nay, He repelled it by His heavenly majesty.”NPNF1: Vol. V, Augustin’s Anti-Pelagian Works, The Grace of Christ And on Original Sin, Book II On Original Sin, Chapter 47. This same citation of Ambrose is likewise found in John E. Rotelle, O.S.A., ed., Works of Saint Augustine, Answer to the Pelagians III, Unfinished Work in Answer to Julian, Book I:66, Part 1, Vol. 25, trans. Roland J. Teske, S.J. (Hyde Park: New City Press, 1999), p. 91; and again later in the same work, 4:121, p. 485; as well as in His Answer to Julian, as set forth above.