Are babies born guilty of Adam's sin? What is original sin?

John Chrysostom c. 349–407 ADHomilies on Romans 10.2–3, on Romans 5:19

What is the question? It is the saying that through one man's disobedience many were made sinners. That when he sinned and became mortal, those born of him should be mortal too is not strange. But that another should become a sinner from his disobedience, what sense would that make? ... What then does "sinners" mean here? To me it seems to mean liable to punishment and condemned to death.

The Eastern reading: from Adam we inherit death and its weakness. Orthodox writers today call it "ancestral sin" and do not speak of inherited guilt.

Pelagians (as Augustine reports)Augustine, On the Merits and Forgiveness of Sins 1.9

They hold that the death mentioned there is not the body's, which they deny Adam earned by sinning, but the soul's, which happens in sin itself, and that sin itself passed from the first man to others not by descent but by imitation. That is why they refuse to believe that original sin is removed in infants by baptism, since they say there is none at all in newborns.

Augustine's first anti-Pelagian book, written for the imperial official Marcellinus.

Augustine of Hippo 354–430 ADCity of God 13.14

God, the author of natures, not of faults, created man upright. But man, corrupted by his own will and justly condemned, begot corrupted and condemned offspring. For we were all in that one man, when we all were that one man who fell into sin through the woman who was made from him before sin.

Augustine read Romans 5:12 in Latin, "in whom all sinned". The Greek can also mean "because all sinned".

Augustine of Hippo 354–430 ADAgainst Julian Book 4

Understand how John could say that little children have no sins: not because they are not held bound by the sin of the first human beings, but because they have committed none of their own.

Augustine's full reply to Julian (421). Julian had appealed to Chrysostom ('John'); Augustine answers that infants have no sins of their own, but are held by the first man's sin all the same.

Julian of Eclanum c. 386–c. 455 ADTo Florus, quoted in Augustine's Unfinished Work against Julian 1.123

Evil, then, is not part of nature, and God cannot create guilty people or place them in the devil's kingdom. These conclusions show you to be a Manichaean, indeed worse than a Manichaean. They also make clear that humanity enters this world without sin, that the fruit of human fertility is under God's authority rather than the devil's, and that nature is innocent.

Julian, a bishop deposed in 418, was the sharpest critic of Augustine's doctrine. His words survive only inside Augustine's reply.

Council of TrentSession 5, Decree on Original Sin Canon 2

If anyone asserts that Adam's sin harmed him alone and not his descendants ... or that, defiled by the sin of disobedience, he passed on only death and bodily punishments to the whole human race, but not sin, which is the death of the soul: let him be anathema, for he contradicts the apostle, who says: "Through one man sin entered the world, and through sin death, and so death passed to all men, in whom all sinned" (Romans 5:12).

Trent repeats Orange (529), canon 2.