Thomas Aquinas and the Immaculate Conception

If the doctrine of the Immaculate Conception was held by the Church as true right from the start, why then would St. Thomas Aquinas not believe that Mary was immaculately conceived? I mean, that was already the 13th century. Apparently, the doctrine was not all that clear cut.

He did not disbelieve the idea. There were theologians who advocated for the definition of the idea by the Church. Aquinas, however, perceived a logical flaw for which the Church had no ready explanation: namely, if Mary was immaculately conceived, she would have no need for a redeemer. That idea bothered Aquinas, and nobody could offer a suitable explanation.

Aquinas felt that the Church would look quite stupid if She promulgated a doctrine for which questions could be raised that the Church had no answer for. Aquinas felt that the Church ought to be able to answer that question before She taught this doctrine.

And, indeed, when the doctrine was finally promulgated, the Church explained (after centuries of theological discussion) that the merits of Calvary were applied to Mary in advance of her birth, because God and spiritual matters are not constrained by the sequence of time (an idea that was in its infancy during Aquinas’ lifetime).

Aquinas did not feel that the idea should never be promulgated - he only (wisely) counseled that the time was not right because the Church’s understanding was not sufficiently complete. ALL doctrine develops, but this particular doctrine had not developed sufficiently. The Church (wisely) tabled the matter at the time, mainly on the strength of Aquinas’ argument.

Aquinas, as usual, was correct.

If Aquinas did not disbelieve it then why did he state in writing "Christ excelled the Blessed Virgin in this, that he was conceived and born without original sin, while the Blessed Virgin was conceived in original sin, but was not born in it."

Whether he later changed his mind I don’t know but that is a clear and unambiguous declaration from The Catechetical Instructions of St Thomas Aquinas that he did NOT believe in the Immaculate Conception.

The other point is that the Immaculate Conception was not dogma then so he was not contradicting the Church.

Not really a huge fan of the concept of the Immaculate Conception generally. I think the Orthodox have this one “more right.”

This article addresses your question:

If the divinity of Christ was a doctrine held by the Church right from the start, why was it disputed in the 4th century? Any dogma can be come challenged, even by well-meaning people–it’s why we have an infallible teaching authority to call all back to the unity of faith.

St. Thomas Aquinas went back and forth and ultimately affirmed it–unfortunately, he argued against it in his most famous work, the Summa (although, in his period of denial, he still believed her to be sanctified in the womb immediately after conception).

First, he affirmed it: “Such was the purity of the Blessed Virgin Mary, who was exempt from both original and actual sin.” [Com. in I Sent, d. 44, q. 1, a. 3, ad 3]

Later, in the Summa, he explicitely denies it: “The Blessed Virgin did indeed contract original sin.” [Summa theologiae IIIa, q. 27, a. 2, ad 2]

Ultimately, though, he accepted it: “For she was most pure because she incurred the stain neither of original sin nor of mortal sin nor of venial sin.”[Expositio super salutatione angelica]

Thomas Aquinas was wrong. That’s all there is to it.

Nowhere does it say that everything every saint or doctor of the Church wrote was without error. In this case, the Saint just didn’t get it right.

The Church has declared the Immaculate Conception to be dogma and so there really is nothing more to discuss.


A dogma is a truth revealed by God. A truth not revealed by God cannot suddenly become a truth revealed by God after the death of the last Apostle. The Immaculate Conception was therefore always a dogma, but its handing on by the ordinary Magisterium had become obscured a bit in St. Thomas’s time and the Church had not issued an extraordinary definitive judgment on the issue. Being wrong is not a sin when you are in good faith, which St. Thomas certainly was. In such cases, the faith of the Church covers you, as Pope Innocent IV wrote: “In that case, the faith of the Church replaces his opinion, though his opinion is false, it is not his faith, but his faith is the faith of the Church.” (Innovent IV, Commentaria in quinque libros decretalia, Ad liber I)

“Revealed truth” is an ongoing problem for systems that rely heavily on revelation. Here. a Saint and Church Father was obviously in disagreement with an idea that someone(s) felt had been revealed to them…it was not a dogma in his time and to somehow make it so does not fit the facts. The fact that it had to be declared in 1854 shows that there was a great deal of disagreement.

Actually, there was a much simpler out for the Church. Since they believe that Jesus is God and therefore, eternal, Mary was simply saved from all time. Of course that brings in other thorny issues like predestination.

Glad you agree with me.

Am I looking at this too simply? There seems to be agreement that Mary was free from Original Sin when she was born.

The debate is whether she was kept from OS at the moment of conception or conceived with OS and cleansed while in utero is it not? If so, then who can decide dogmatically what is true? Only the Church and the Church has said the former.

Individual Catholics, even Aquinas, are free to ponder, debate and discuss but they cannot dismiss what the Church has said is a truth.

The difference is, when in the early church people challenged a dogma, they were (rightfully) labeled heretics. Think about Arius, for instance. So either:

  1. the teaching wasn’t dogma or wasn’t taught since the start
  2. Aquinas was a heretic in this regard

I opt for no. 1.

You are right that he was wrong, and of course I’m not one of those who believes that Aquinas was always right. But my point is, the doctrine obviously wasn’t consistently taught or believed in the medieval Church. So we can’t hold the doctrine of the Immaculate Conception as a teaching that was held right from the start, as some claim.

The fact that the Immaculate Conception is dogma today is proof beyond question that it was part of the original deposit of faith.

All dogmas are either part of the original deposit of faith or they are invented. Those are the only two options. It is either revealed truth or it is made up. Those are your only choices.


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