How to Caterina.

Nowhere in the article was written and said that St. Thomas was “versus” the Immaculate Conception, it only makes reference - and with all due rigor historical and theological - to those who "opposed phases of preliminary studies".

Let me clarify everything with an example of "opposition" within the disputations or preliminary studies: the Patriarch of Venice, Card. Albino Luciani, future John Paul I, was not favorable to those who later will be the contents of the Human life. Just though Paul VI spoke out and established a precise discipline of the Church in matters, he summoned his clergy and said: "Many of you know what I was thinking during the debates on the subject, but now the discussions and debates are over, the Pope has spoken with a Encyclical and what he has established is binding doctrine of the Church ".

Dogmatic theology is a complex matter to which you can not have an approach "devotional" or "catechetical", why do or speculate in dogmatic theology is another thing and requires other assumptions, otherwise it can happen, as in this case, that you take two words, and fraintendano, do not read the penalty that has been written – although clearly, precise and documented – and finally meets the merits of what was not said.

The article was reported faithfully translated into Italian (seen that many readers do not know Latin) the textual expression that encompasses the concept of St. Thomas, exactly this under:

[…] The future doctor Angelicus considered the Blessed Virgin resplendent holiness, however, did not provide the Immaculate Conception, but she had been purified from original sin after the infusion of the soul. Because if the Blessed Virgin "was conceived without original sin, would have had no need of Christ's redemption, and so Christ would not be the universal redeemer of men: which impairs his dignity» [Sum of Theology, III, q. 27, articles. 1-6].

Caution, because the concept of “purification” from original sin, occurred “after infusion of the soul“, requires further clarification. St. Thomas in fact follows the Aristotelian theory (Book of the generation of animals, (II), III, 736A35), he specifically mentioned (QUESTION, III, 33, ob. 3), according to which “in subsequent times the body is formed and prepared to receive the soul”. So the matter of the body is humanly animated - ie receives the human soul - not the instant of conception, but around the 40th day after conception. We first fact the living reality - the alive -, then reality animal - l 'animal -, and finally the human reality - l 'homo – (therein), that “absorbs”, includes and “oversteps” previous (therein, I, 118, 2, 2m)”.
Post then this conception Thomasian, affirm that the Blessed Virgin would be “released” from original sin after the infusion of the soul, mean to say that this would happen around the 40th day of life.

The fact that in the past, the Dominican theologians, were adverse to what would later become the truths of faith and dogma proclaimed, I don't say it, Telling the story; a story that certainly can not be canceled through a devotional phrase of St. Catherine of Siena quoted out of place in the precise and specific historical context-dogmatic to which this article adheres scrupulously and clarity.
At the bottom of this paper was also annexed the text of the study of a Thomist philosopher and theologian dogmatic, Mgr. Cristoforo Charamsa, who is a devoted Marian and a Thomist in the round; invitation to read it because it is really enlightening.

Initially St. Thomas, in his "juvenile phase" was in favor of the doctrine of the Immaculate Conception of the Blessed Virgin, But when several theologians began to assert that the Virgin Mary would not have been redeemed by Christ, he "shuddered" and reacted by denying its exemption from original sin; and this is a historical and theological-speculative documented, not however as you say a “obsession”.
With impeccable logic speculative philosophical-theological own St. Thomas that because it became the largest that still is, the Doctor Angelicus remade in St. Paul says that as in the sin of Adam all have sinned and therefore all had need of Christ's redemption: «Through the disobedience of one man the many were made sinners» (RM 5,19). It's still; «As a result of one man sin entered into the world, and through sin death, and so death passed upon all men, because all sinned» (RM 5,12).

Aquinas stated, then, that Mary, soon after conception, received an extraordinary sanctification in his soul, that erased the original sin.
Historical sources Dominican report that towards the end of his life, St. Thomas, during talks that he held in Naples, demoted from his position and went back to her that instead had matured in his youth.

Was not the only St. Thomas Aquinas, devoted to the Virgin Mary, because even other saints equally worshipful denied her Immaculate Conception: St. Bernard of Clairvaux and St. Albert the Great, also doctors of the Church.
Sant'Anselmo d'Aosta, which basically goes back to Aquinas, argued that the Blessed Virgin was conceived in original sin as everyone from which was prematurely redeemed by Christ before his birth. The thesis of the "early redemption" is also applied in the speculations of Bernard of Clairvaux, Alexander of Hales, of Bonaventure of Bagnoregio, addition to the aforementioned Albert the Great and St. Bernard of Clairvaux.

The Church has taken into account the sum Aquinas' thought to the point that in the definition of the dogma of the Immaculate Conception, occurred under the pontificate of Blessed Pius IX, was written very clearly that "Maria, in view of the merits of Christ, redeemed in a unique way». In other words: for the Blessed Virgin Mary has been implemented a pre-redemption, ie was preserved from original sin from the first moment of her conception: without original sin (conceived without original sin).

This is the dogmatic teaching of the Church, gained after many centuries, because only in 1854 was proclaimed the dogma of the Immaculate Conception as such established a truth of faith that closed, from then on, all legitimate and rightful theological discussions on the subject took place earlier.