It ought to be well-known that Rome’s dogma of the Immaculate Conception was denied by her leading medieval saint, Thomas Aquinas (as outlined here). This has been something of a thorn in the side of those contending that Mary was immaculately conceived. They have tried to explain Aquinas’ position away in various ways – such as by arguing that Aquinas didn’t believe that life begins at conception (which is true, but not particularly helpful to their case). Another theory sometimes set forth (recently, for example, by Taylor Marshall) is that Aquinas came to hold to the dogma of the immaculate conception late in life, even after writing the portion of the Summa Theologica that denies it.
RÃ©ginald Marie Garrigou-Lagrange, O.P. is (or, I suppose I should say, “was”) one of the leading Thomist theologians of the 20th century. In his Discourse II on Mary’s Immaculate Conception, published in “The Mother of the Savior” (1948), Garrigou-Lagrange wrote:
In the final period of his career, when writing the Exposito super salutatione angelica—-which is certainly authentic —–in 1272 or 1273, St. Thomas expressed himself thus: ‘For she [the Blessed Virgin] was most pure in the matter of fault (quantum ad culpam) and incurred neither Original nor mental nor venial sin.’
The problem is this:
The “neither original” in that quotation is an interpolation. Gibbings pointed that out long ago in his “Roman forgeries and falsifications” but you can see for yourself if you get a modern critical text of the work.