As we prepare for the solemnity of the Immaculate Conception of the Blessed Virgin Mary, Thomists are forced to face the rather popular criticism: “You know, St. Thomas doesn’t know everything. After all, he denied the Immaculate Conception!”
Beyond the obvious fact that no good Thomist would ever hold that St. Thomas knew literally everything in the first place, and the fact that nearly every person in St. Thomas’ day who held the Immaculate Conception held the dogma in a heretical way (claiming that our Lady did not need a Redeemer), and also the further point that most of the best theologians of the 12th and 13th centuries also seem to have denied the doctrine (including Sts. Bernard, Anselm, Albert the Great, and Bonaventure, as well as Peter Lombard and Hugh of St. Victor); beyond all of that, there is this little point: St. Thomas did not (most probably) deny the Immaculate Conception after all.
St. Thomas’ teaching in the Summa Theologica
In the Summa (ST III, q.27, a.1-2), fighting against the false idea of some who held both that Mary was conceived without sin and also that she did not need to be redeemed by the merits of Christ, St. Thomas refuses to commit himself to the doctrine of the Immaculate Conception. It seemed to most theologians (and also to St. Thomas) that, if Mary were conceived without sin, then she would not need a Redeemer – just as Adam would not have needed a Redeemer if he had not sinned. However, we know by faith that Mary was indeed redeemed by Christ, therefore, it seemed to St. Thomas that she could not have been conceived immaculate.
Still, in the Summa, he very clearly states that she was cleansed from sin shortly after conception and while yet in the womb. He holds that her sanctification was preeminent and singular.
While there is certainly some theological confusion in his thought, a good deal of the error in St. Thomas’ consideration of the Immaculate Conception stems from a mistaken understanding of the process of generation and the formation of the child in the womb. St. Thomas (together with others) believed that the body was conceived before the rational soul was created. Hence, his main argument is to prove that our Lady could not have been sanctified before the creation and infusion of her rational soul – and this we can still hold today, Mary was not sanctified before her animation because she was not immaculately conceived before her conception.
However, St. Thomas errs when he goes further and states that Mary was sanctified after her conception – for she was, in fact sanctified in the moment of her conception. Still, even here, St. Thomas' main point is to show that Mary incurred the debt of original sin (which is correct), though he mistakenly also gave her the stain of original sin as well (which is incorrect).
Thus, even in the Summa, St. Thomas is not entirely wrong – and he very clearly wants to place the sanctification of our Lady as close to the very moment of her conception as possible, but he does not yet see how to hold the Immaculate Conception while at the same time holding that our Lady needed to be redeemed by Christ.
Three stages in the Angelic Doctor’s thought
What most people do not know is that St. Thomas’ thought on this issue developed over three stages. The Summa (where he seems to deny the dogma) is the second stage, but in the first and third stages it seems that he believed in the Immaculate Conception.
As a young theologian, St. Thomas commented on the Sentences of Peter Lombard. In that commentary he wrote: “Purity is increased by withdrawing from its opposite: hence there can be a creature than whom no more pure is possible in creation, if it be free from all contagion of sin: and such was the purity of the Blessed Virgin who was immune from original and actual sin.” (I Sent., d.44, q.1, a.3, ad 3) From this, it is quite clear that St. Thomas affirmed the dogma of the Immaculate Conception when he was first beginning his theological career.
The third stage came in the final period of his life, when St. Thomas commented on the Angelic Salutation (around 1272 or 1273) he wrote: “For she (the Blessed Virgin) was most pure in the matter of fault and incurred neither original nor mental nor venial sin.” There is some textual variance among manuscripts, but sixteen out of the best nineteen manuscripts read as above and show that St. Thomas did indeed end his life holding to the belief in the Immaculate Conception. Further, there are several other places in the later works of the Common Doctor where it seems that he affirms the dogma.
At least this much is certain, St. Thomas ended his life leaning much closer to a belief in the Immaculate Conception and was convinced that our Lady received a singular grace in being free from all sin, both actual and even original sin. Therefore, it is ridiculous and quite unfair (not to mention uncharitable) for people to claim that St. Thomas denied the dogma of the Immaculate Conception.
For a further study of St. Thomas’ view on the Immaculate Conception, consider the excellent book by Fr. Reginald Garrigou-Lagrange, “The Mother of the Savior” – particularly Part I, Chapter II, Article II: The privilege of the Immaculate Conception (it is here that he discusses St. Thomas’ thought on the matter).