At an early stage of his
theological career, St. Thomas may even have believed in the immaculate
conception himself. In his commentary on the first book of the Sentences (around
1252-54), he writes:
Purity is understood by withdrawal
from the contrary. And thus, we can find something created than which nothing
can be more pure among created things, if it is not stained by any contagion of
sin. And such was the purity of the Blessed Virgin Mary, who was immune from
original and actual sin, though beneath God inasmuch as there was the power to
sin in her.
However, this text is not unambiguously
referring to the immaculate conception. Given the context of the article, it is
more likely that St. Thomas means to assert only that Mary was cleansed of
original sin and thus became immune from it before her own birth. This is clear
by the comparison with what he says when commenting on the third book of the
Sentences: “Being without sin is said to be proper to Christ because he was
never infected with either the original stain or any actual sin. His virgin
mother, however, was infected with original sin, from which she was cleansed
before she came out of the womb, but she was totally immune from actual sin.”
Elsewhere, just a few lines after affirming that “the Blessed Virgin did contract
original sin,” Aquinas adds that “in her birth [ortu] she was immune
from original sin.” In other words, calling Mary immune from original sin does not
mean she never had original sin, only that she was cleansed of it. (Dylan
Schrader, “Appendix 1: Thomas Aquinas on the Immaculate Conception,” in Mary,
Mother of God’s Word Made Flesh [Sacra Doctrina; Washington, D.C.: The
Catholic University of America Press, 2026], 250-51)
