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St. Thomas, Doctor of the Immaculate Conception?

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Throughout the history of the interpretation of St. Thomas's mariology, there has always been a controversy surrounding his true position in relation to the conception of Our Lady. Some interpret St. Thomas as denying the Immaculate Conception, others as affirming it, and others as having various stages in his life (affirmation to doubt to affirmation). Yet, from a consideration of St. Thomas' entire corpus, his orthodoxy becomes abundantly clear.

In this article, I seek to make this orthodoxy clear by an analysis of his passage on this topic in his Compendium Theologiae which was written during the time of his (in)famous question on the topic in Tertia Pars of his immortal Summa. The advantage of using the Compendium for such an analysis is the compact prose and lucid prose style of the Compendium rather than the tighter, quaestio format of the Summa.


Paragraph 1: As appears from the foregoing exposition, the Blessed Virgin Mary became the mother of God’s Son by conceiving of the Holy Spirit. Therefore, it was fitting that she should be adorned with the highest degree of purity, that she might be made conformable to such a Son. And so we are to believe that she was free from every stain of actual sin—not only of mortal sin but of venial sin. Such freedom from sin can pertain to none of the saints after Christ, as we know from 1 John 1:8: If we say that we have no sin, we deceive ourselves, and the truth is not in us. But what is said in the Canticle of Canticles 4:7, You are all fair, my love; there is no flaw in you, can well be understood of the Blessed Virgin, Mother of God.

Here, there is no controversy.

Paragraph 2: Mary was not only free from actual sin, but she was also, by a special privilege, cleansed from original sin.

At this point, there may, perhaps, be controversy. For, what is the meaning of this "cleansing." This term is used in connection with the term "sanctify" by St. Thomas (e.g., in ST.III.Q27.A2.Rep2).

First, St. Thomas defines the term as "the purification from the filth of corruption is not to be understood as the removal of anything existing, but an impediment to any future filth." (Sent.III.D3.Q1.A2.qa2.Rep2) St. Thomas actually DENIES the possible misinterpretation of his terminology here, by denying that it is "the removal of anything existing."

Second, this "purification" was a universal term used for the description of the privilege given to Our Lady, both by supporters (as in Bl. Scotus) and enemies alike.

Yet, one may be confused by this phrase "original sin" that is used. In the thought of St. Thomas (a concept which is clarified in the Baroque era), there are two uses to the phrase. First, it can be used for the privation of original justice in the soul, e.g., just as the blind eye has a privation of sight (a form it ought to have), so also does the soul have a privation of the gifts given to it in creation. This first way is how we ordinarily use the phrase "original sin." For those who teach that St. Thomas denied the Immaculate Conception, they would need to demonstrate that St. Thomas meant "original sin" in this way.

Second, the term can be used in the sense of a debitum, i.e., “universal necessity or need of being subject to it.” (Pohle) Modern Catholic Theologians explicitly affirm that it was this that Our Lady had before her immaculate conception (i.e., this was frustrated from taking effect in the soul). This can be distinguished between the debitum remotum which flows from the fact that the child was conceived by parents who have the fomes peccati, i.e., certain flames of lust in conceiving the child. Further, there is the debitum proximum which comes from the fact that one is of the seminal ratio of Adam.

In order to explain why this twofold distinction becomes so important in this debate, we must consider the nature of medieval embryology. The medievals distinguished between conception proper (first conception) and animation (second conception). They believed that the body was formed at the first conception by a certain mixture of semen and menstrual blood. Then, 40 days later, this body was "animated" by the infusion of a rational soul. This is the "second conception" or "animation."

So, in explaining the manner in which conception related to the contraction of original sin, we can show the flow thus:

Intercourse from parents with the fomes peccati --> First Conception (of body) with the debitum (frequently called the “stain of original sin” or just “original sin”) --> second conception (infusion of rational soul) --> contraction of original sin (in the sense of the privation of original justice) by the contact of the rational soul with the body which had the debitum

This process is outlined by St. Thomas in Sent.II.D32.Q2 where he labels the debitum as simply "original sin" or the "stain of original sin” (the same terminology which is used in his writing on the purification).

The elasticity of the phrase "stain of sin" is also seen in its use for the fomes peccati as well, "stain of sin or fomes." (ST.III.Q27.A3.Rep3)

Now that we have these primary distinctions in place, we can explain how St. Thomas was justified in saying "she was also, by a special privilege, cleansed from original sin."

St. Thomas, along with all Catholic theologians (with the exception of some early Scotists) affirmed that at first conception Our Lady contracted the debt of original sin (which is commonly just labeled "original sin" or the "stain of original sin"). Then, the rational soul is infused into Our Lady which is given a "singular grace" wherein "original sin" (in the sense of privation of original justice) is not CONTRACTED. St. Thomas' opponents are not those who affirm the Immaculate Conception, but, those who deny the debitum in the body of Our Lady and those who deny that the debitum is cleansed through grace, whose subject is only the soul (both of which would place Our Lady outside the redemption of Christ).

This reading will become clear as we continue the exposition.

She had, indeed, to be conceived with original sin,

Notice, this is in reference to her conception, i.e., her first conception. How could this be in reference to original sin as the privation of original justice in the soul when St. Thomas denied that Our Lady had a rational soul at first conception? Certainly, he is speaking of the debitum here.

inasmuch as her conception resulted from the commingling of both sexes: for this privilege was reserved exclusively to her who as a virgin conceived the Son of God. But the commingling of the sexes which, after the sin of our first parent, cannot take place without lust, transmits original sin to the offspring.

This requires some explanation. St. Thomas affirmed (as stated above) that "from the act of nature that is the propagation of the flesh, there is left a kind of disposition inclining to evil in the very nature of the one generated, which we call concupiscence or the fomes." (Sent.II.D32.Q1.A1.C) This concupiscence in the parents is the principle whereby the debt of original sin is passed on to the bodies of the children.

Now, the parents of the Blessed Virgin Mary were not freed from the fomes, so they still passed on this debitum in the generative act whereby they conceived the Blessed Virgin Mary (this is why parents who are freed from original sin by baptism do not produce children without original sin, i.e., because they still have the fomes peccati). This is why he says that this was because of "the commingling of both sexes."

To deny this, as St. Thomas continues to point out, would actually be derogatory to the glory of the Blessed Virgin. For, the Blessed Virgin (in what St. Thomas calls the "second sanctification") was cleansed from the fomes that she inherited from her parents. St. Thomas clarifies in Sent.III.D3.Q1.A2.qa1 and ST.III.Q27.A3 did NOT have the aspect of concupiscence to it, and in the Compendium Theologiae he says “the Blessed Virgin Mary, however, the lower powers were not so completely subject to reason as never to experience any movement not preordained by reason. Yet they were so restrained by the power of grace that they were at no time aroused contrary to reason. Because of this we usually say that after the Blessed Virgin was sanctified the fomes peccati remained in her according to its substance, but that it was shackled.” (CT.BookI.C224.9)

Thus, the Blessed Virgin was completely unique in being able to conceive a child that was without even the debitum of original sin and thus completely free from Adam.

The last sentence fits better in this interpretative framework (which adequately brings together the entire corpus of St. Thomas) as well. For, from the lust of the parents, the original sin is only brought forth secundum quid, not as some substance derived from the parents, but, as a disposition of the body which, upon contact with the soul, brings about original sin. It is the debitum which principally brings about this contraction.

Likewise, if Mary had been conceived without original sin, she would not have had to be redeemed by Christ, and so Christ would not be the universal redeemer of men, which detracts from his dignity.

If we continue to follow the logic of St. Thomas, this passage continues to make sense. For, if Our Lady had not the debitum what would Christ be redeeming Our Lady from in this singular grace as described? Nothing. This is why it is unacceptable to deny the idea of the debitum (as some earlier Scotists had done). Christ is the redeemer of Our Lady because, through His grace, he stopped the debitum in the body from taking effect in the soul of Our Lady (as normal animation would be so).

Accordingly, we must hold that she was conceived with original sin, but was cleansed from it in some special way.

Again, we must go back to St. Thomas' embryology and understand that "conception" and "animation" are distinct. It would be nonsensical to deny that at the conception of her body that there was the debitum (for, her parents had the fomes and she was a daughter of Adam, i.e., within his seminal ratio...if this was not the case, this would put her outside of the redemption of Christ) or to affirm that there was this cleansing at a moment in which she did not have a soul, for, as Bl. Scotus teaches "the Blessed Virgin was not sanctified before her animation, because the flesh, as it is not the subject of sin, so neither is it of sanctifying grace."

Paragraph 3+4: Some men are cleansed from original sin after their birth from the womb, as is the case with those who are sanctified in baptism. Others are reported to have been sanctified in the wombs of their mothers, in virtue of an extraordinary privilege of grace. Thus we are told with regard to Jeremiah: Before I formed you in the womb I knew you; and before you came forth out of the womb I sanctified you (Jer 1:5). And in Luke 1:15 the angel says of John the Baptist: He will be filled with the Holy Spirit even from his mother’s womb.

We cannot suppose that the favor granted to the precursor of Christ and to the prophet was denied to Christ’s own mother. Therefore, we believe that she was sanctified in her mother’s womb, that is, before she was born.

All is good thus far.

Paragraph 5: Yet such sanctification did not precede the infusion of her soul.

This is clearly a point of agreement between the theologians (as the quote from Bl. Scotus above shows).

In that case she would never have been subject to original sin, and so would have had no need of redemption.

NOTICE, this is so incredibly important what he says here. He describes Our Lady, before the animation of the soul as being SUBJECT TO ORIGINAL SIN. Tell me, those who say that St. Thomas denied the Immaculate Conception, how could a body without a soul have a privation of original justice which only applies to the soul? The answer, of course, is that St. Thomas is NOT referring to such a privation, but the debt of original sin in the body of Our Lady.

For only a rational creature can be the subject of sin. Furthermore, the grace of sanctification is rooted primarily in the soul, and cannot extend to the body except through the soul.

Then, he proves the point. For, he clearly is affirming here that Our Lady, before animation, was not a "rational creature" and did not have a "soul." Further, he intimates the manner in which the graces of Immaculate Conception flows. There is the sanctification which is "rooted in the soul" and then "extend[s] to the body." Now, what kind of sanctification could happen "to the body?" I'm glad you asked! The type of sanctification would be the sanctification of the DEBITUM which is located in the body (further confirming my reading).

Hence we must believe that Mary was sanctified after the infusion of her soul.

Yet, there is a difficulty here. The objector may respond "How can you say that St. Thomas affirms the Immaculate Conception when he affirms that the sanctification is after the infusion?"

Yet, we must distinguish between an "after" in nature vs. an "after" in time. The former obtains without a lapse of time, but in the "first instance" or "immediately" after some things are constituted. This is actually distinguished by Bl. Scotus when he writes "just as God could infuse the grace, by which original sin is destroyed, in subsequent instants, so he could do it also in any antecedent instant, and therefore also in the first, in which, that is to say, she was understood, on the part of her substance, to be in existence."

Yet, the objector may continue "well, I grant the distinction, yet how may we know that St. Thomas affirmed the proper part of the distinction and did not intend to affirm a temporal posteriority?"

In another place, St. Thomas clarifies himself to say that "immediately after conception and the infusion of the soul she was sanctified" (QVI.Q5.A1) is the common position (and the one he presumably accepts). Otherwise, he does not specify.

Yet, from a quick reductio we can see that St. Thomas couldn’t have meant a period of time that elapsed after her animation, for, if this was so it would be the removal of some filth existing. Yet, St. Thomas denies that the sanctification of the Blessed Virgin is the “removal of [some filth] existing.” (c.f., above) Therefore…

Yet, in any case, to add a period of time when "after" is used is to make an artificial addition that does not flow from the words of St. Thomas.


At this point, the reading I presented should be clear and present less difficulties than the contrary reading. Such a reading could be given of the other relevant sections (Sent.III.D3.Q1; QVI.Q5.A1; Psalm.Ps45; Jerem.C1.L3), a greater exposition of the relevant principles (debitum culpae, fomes peccati, etc.), and research done into other scholastics of the golden age, yet, the basic hermeneutical structure has been properly outlined.

St. Thomas Aquinas, Worthy child of the Queen of Virgins, pray for us.

1,652 views4 comments


"If we continue to follow the logic of St. Thomas, this passage continues to make sense. For, if Our Lady had not the debitum what would Christ be redeeming Our Lady from in this singular grace as described? Nothing."

Redeeming her from the debitum?


Thanks for this, it's helpful. My difficulty is the following... If the "fomes" is or is part of the stain of original sin, it would seem that we must insist strongly that we do indeed encounter an error in ST III-27-3-3 (etc.)... Thomas' treatment of the consequences of the Incarnation for the BVM appears to be simply materially heretical, as ID lays down that the BVM is preserved from all stain of sin from the first moment of her conception; you must either show that Pius IX means "second conception" or "ensoulment" (difficult given it is 1854, a decade after the advent of modern medicine on such things), or that he means something other than the "fomes" by "stain of…

Replying to

Thanks for this awesome write-up. You've convinced me that St. Thomas' understanding of "stain" includes the notion of debitum. I have two questions:

First, can you help me understand this Del Prado text in your comment? It seems like he's saying that, with the context of Monsignor Bruni, the definition used the term "person" to convey that the fomes were excluded from Mary's Conception. Is it really the case that it is still an acceptable position to hold that the fomes are just bound in actu primo and not extinct? Fr. Maguire OFM wrote in 1963 that, while everyone denies that concupiscence existed in Our Lady in act, the extinction of concupiscence even in actu primo from her conception is…

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