Chapter VI.
On the transmission of original sin.
Now the mode of transmission of original sin is this: that although the soul is not from propagation, nevertheless original guilt passes from the soul of Adam to the souls of his posterity through the medium of the flesh generated through concupiscence, so that, just as the flesh of Adam was infected by the sinning soul and made prone to lust, so the flesh, sown through lust and carrying with it the vitiated infection, infects and vitiates the soul; which infection in the soul is not only punishment, but also guilt. And thus the person corrupts nature, and corrupted nature corrupts the person, divine justice being preserved in all things, to which the infection of the soul can in no way be imputed, although He infuses it by creating and by infusing unites it with infected flesh.
Now the reason for understanding the aforesaid is this: because, since the first principle made man in His own image for the expression of Himself, He so constituted him on the part of the body that all men would be propagated from the first man as from one radical principle; and so on the part of the soul, that on account of the expressed likeness, both in being and enduring as well as in understanding and loving, all rational spirits would emanate immediately from God Himself as from the first and immediate principle. And since the spirit, as the more excellent, approaches nearer to the first principle, God so constituted man that the spirit would preside over the body, and the body would be subject to the created spirit, so long as it obeyed the uncreated Spirit; and conversely, if the spirit did not obey God, by the just judgment of God his body would begin to rebel against him: which indeed happened when Adam sinned.
Therefore, just as, if Adam had stood firm, his body would have been obedient to the spirit, and he would have transmitted such a body to his posterity, and God would have infused a soul into it, so that, united to an immortal body obedient to it, it would have possessed the order of justice and immunity from all punishment: so, from the time that Adam sinned and the flesh was made rebellious to the spirit, it is necessary that he transmit such flesh to his posterity, and that God infuse the soul according to the primary institution; but the soul, when it is united to rebellious flesh, incurs a defect in the order of natural justice, by which it was bound to rule over all inferior things. And because the soul is united to the flesh, it is necessary that it draw the flesh, or be drawn by it; and because it cannot draw the flesh as rebellious, it is necessary that it be drawn by it and incur the disease of concupiscence. And thus it incurs at once the lack of due justice and the disease of concupiscence; from which two, as from aversion and conversion, original sin is said to be constituted, according to Augustine and Anselm.
Since therefore it was most well-ordered that human nature should be so created, and that once created it should be so propagated, and that once sinning it should be so punished, as was said before, such that in creation the order of wisdom is preserved; in propagation, the order of nature; in punishment, the order of justice: it is clear that it is not against divine justice if fault is transmitted to posterity.
Again, because original fault could not be transfused into the soul unless the punishment of rebellion in the flesh preceded; and there would be no punishment unless fault had preceded; nor did fault proceed from an ordered will, but from a disordered one, and thereby not from the divine will, but from the human: it is therefore clear that the transfusion of original sin is from the sin of the first man, not from God, not from created nature, but from the vice committed. And thus what Augustine says is true, that "original sin is not transmitted to posterity by propagation, but by concupiscence."