St. Thomas affirming the Immaculate Conception!

[Geremia]

Not to split hairs, but St. Thomas is in agreement with the Church if we consider conception to be the two-fold act that it is. On the one hand, there is the physical conception of the body; on the other, there is the spiritual conception of the soul animating that body. Both of these conceptions (the conception of the body and soul) happen in exactly the same instant in time, but the conception of the body necessarily precedes the conception of the soul in the ontological order. God doesn't create the soul until the body is conceived, so in the order of creation the existence of the body is logically and ontologically prior to the existence of the soul, though they are both created in the same temporal instant. Therefore, it is entirely possible that our Lady was physically conceived in Original Sin but spiritually conceived exempt from it, such that, at the very instant the soul was infused into the body (the moment of conception), the body no longer manifested the effects of original sin, though it retained all of its physical characteristics.By the action of man, she is conceived in Original Sin and, hence, from this perspective, St. Thomas is correct is pointing out she needs to be redeemed as Scripture says all men do.  But by the action of God, her soul is conceived exempt from it and so she is properly conceived without sin as the Immaculate Conception. Thus, Mary could in a sense physically appear to be like everyone else (and thus not draw undue attention to herself) while being free from the debilitating effects of Original Sin, both spiritual and physical.

EDIT:

The Church speaks of "conception" as a temporal instant, in which case it truly was the Immaculate Conception. However, the philosophers (like St. Thomas) distinguished the temporal order from the ontological order. It is this order that a cause may precede an effect, which both happen at the same temporal instant. Perhaps St. Thomas' dilemma concerned the prevalent opinion of his generation concerning the time between conception and ensoulment, known as "quickening." It was commonly believed that the body was conceived for some time in the womb before the soul was created to animate that body.  Progress in biological research has since shown us that there is every reason to believe that ensoulment takes place at the very instant of conception, though logically posterior to it (since the infusion of the soul logically necessitates the prior existence of the body). The language "conception" in St. Thomas' era would have referred to simple biological conception, anticipating the infusion of the soul. But if they happen simultaneously in time then the conception is truly immaculate, though in the ontological order the body is conceived in sin but sanctified in the same instant by the immaculate soul, free from Original Sin.

(source)

[Gardener]

I'm really surprised to see INPEFESS grasping at straws while trying not to split hairs.

St. Thomas deals with this concept in principle, and it disagrees with INPEFESS' laudable, though misguided, attempt at saving his hero from error.

Note the bold:

I answer that, One thing can be in another in two ways. First, as in its cause, either principal, or instrumental; secondly, as in its subject. Accordingly the original sin of all men was in Adam indeed, as in its principal cause, according to the words of the Apostle (Romans 5:12): "In whom all have sinned": whereas it is in the bodily semen, as in its instrumental cause, since it is by the active power of the semen that original sin together with human nature is transmitted to the child. But original sin can nowise be in the flesh as its subject, but only in the soul.

The reason for this is that, as stated above (I-II:81:1), original sin is transmitted from the will of our first parent to this posterity by a certain movement of generation, in the same way as actual sin is transmitted from any man's will to his other parts. Now in this transmission it is to be observed, that whatever accrues from the motion of the will consenting to sin, to any part of man that can in any way share in that guilt, either as its subject or as its instrument, has the character of sin. Thus from the will consenting to gluttony, concupiscence of food accrues to the concupiscible faculty, and partaking of food accrues to the hand and the mouth, which, in so far as they are moved by the will to sin, are the instruments of sin. But that further action is evoked in the nutritive power and the internal members, which have no natural aptitude for being moved by the will, does not bear the character of guilt.

Accordingly, since the soul can be the subject of guilt, while the flesh, of itself, cannot be the subject of guilt; whatever accrues to the soul from the corruption of the first sin, has the character of guilt, while whatever accrues to the flesh, has the character, not of guilt but of punishment: so that, therefore, the soul is the subject of original sin, and not the flesh.

-S.T., I/II, Q83, Art1
http://www.newadvent.org/summa/2083.htm

Notice INPEFESS' answer tries to state what St. Thomas elucidates as a potential answer, but then denies in the first bolded section. St. Thomas then breaks it down in the last bolded section specifically as to why.

There simply is no "physical conception in Original Sin", according to what St. Thomas himself has to say about the subject as relates to the flesh and the soul. That's novelty par excellence in an attempt to try to salvage Thomas on this point.

Since St. Thomas knew this, he did not try to argue such a thing, for his argument centered on the redemption by Christ of all humanity, which is why he denied the Immaculate Conception as such.

Christ doesn't redeem soulless matter, and Original Sin has nothing to do with the physical body per se. It's all about the soul. In the case of Our Lady, the declaration itself excludes such a weird concept, as the language is overarching, and covers all bases.

"We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful."

Declaramus, pronuntiamus et definimus doctrinam quae tenet beatissimam Virginem Mariam in primo instanti suae conceptionis fuisse singulari Omnipotentis Dei gratia et privilegio, intuitu meritorum Christi Jesu Salvatoris humani generis, ab omni originalis culpae labe praeservatam immunem, esse a Deo revelatam, atque idcirco ab omnibus fidelibus firmiter constanterque credendam.

https://www.ewtn.com/library/papaldoc/p9ineff.htm

I like INPEFESS a lot. But he's wrong.

[Kephapaulos]

I am sorry if I am repeating something here, but I remember reading that Sixtus IV wrote a work explaining that St  Thomas and Bl. Scotus were in the same line of thinking concerning the Immaculate Conception. I don't know if the work is extant or available though. It seems to me that Our Lord was preserving St. Thomas' humility by not allowing him to completely figure it out and want the Franciscans bolstered by more devotion to Our Lady.

[Gardener]

I am sorry if I am repeating something here, but I remember reading that Sixtus IV wrote a work explaining that St  Thomas and Bl. Scotus were in the same line of thinking concerning the Immaculate Conception. I don't know if the work is extant or available though. It seems to me that Our Lord was preserving St. Thomas' humility by not allowing him to completely figure it out and want the Franciscans bolstered by more devotion to Our Lady.

The only real common point between Scotus and Aquinas is the need for redemption by Christ.

Scotus posited that she was redeemed in a sense that she had the merits of Christ applied from the moment of her conception, and thus contracted no stain of Original Sin in light of these merits. Hence, he defended the Immaculate Conception.

Aquinas posited that she contracted Original Sin, even if briefly, and then it was remitted prior to birth -- similar to St. John the Baptist. Obviously that != Immaculate Conception.