Fr. Joseph Pohle's 1914 [iurl=https://isidore.co/calibre/browse/book/3789][i]Mariology: A Dogmatic Treatise on the Blessed Virgin Mary, Mother of God[/i][/iurl] has a section on "The Teaching of St. Thomas" (pp. 67-70):[quote=Fr. Pohle's «Mariology»]5. The Teaching of St. Thomas.

Theologians are divided in their opinion as to what was the mind of St. Thomas in regard to the Immaculate Conception. Some[sup]64[/sup] frankly admit that he opposed what in his day was not yet a defined dogma, but insist that he virtually admitted what he formally denied. Others[sup]65[/sup] claim that the Angelic Doctor expressly defended the Immaculate Conception and that the (about fifteen) adverse passages quoted from his writings must be regarded as later interpolations. Between these extremes stand two other groups of theologians, one of which[sup]66[/sup] holds that St. Thomas was undecided in his attitude towards the Immaculate Conception, while the other[sup]67[/sup] merely maintains the impossibility of proving that he opposed the doctrine.

a) In order to arrive at a just and impartial idea of St. Thomas' position we shall have to study his teaching in connection with what may be called its theological environment. Influenced by the attitude of St. Bernard, who was otherwise an ardent devotee of the Blessed Virgin, all the predecessors and contemporaries of the Angelic Doctor—with the exception perhaps of his fellow Dominican Vincent of Beauvais (d. 1264)—opposed the Immaculate Conception. Of St. Anselm of Canterbury, the "Father of Scholasticism," it has been truly said that, like Aquinas, he virtually asserted the Immaculate Conception in his premises and denied it formally in his conclusions.[sup]68[/sup] It is to Anselm that Scholasticism owes the oft-quoted Mariological principle: "It was meet that the Blessed Virgin should shine in a splendor of purity than which none greater can be conceived under God, that virgin to whom God the Father had determined to give His Son, whom He had begotten as His equal, and whom He loved like Himself,—and He gave Him in such wise that He would be the Son of both God the Father and the Virgin."[sup]69[/sup]

Peter Lombard (d. 1164) taught that "the Blessed Virgin bore the taint of original sin, but was entirely cleansed before she conceived Christ."[sup]70[/sup] This was the common teaching in the Franciscan Order. No wonder that the most eminent theologians of that Order, up to the time of Duns Scotus (d. 1308), battled side by side with the Dominicans.[sup]71[/sup] Not to mention Alexander of Hales (d. 1245), St. Bonaventure, who was one of the greatest lights among the Minorites, while admitting that the doctrine of the Immaculate Conception might be defended as probable on the strength of certain considerations of fitness,[sup]72[/sup] openly espoused the opposite view.[sup]73[/sup]

b) Placed in a theological environment in which the true solution of the problem was not yet attainable, St.Thomas, in common with the most eminent and saintly doctors of his time, had a perfect right to defend a thesis which was by no means regarded as scandalous but open to discussion. The dogma of the Immaculate Conception was still in process of clarification. The Angelic Doctor nowhere expressly teaches the Immaculate Conception of the Blessed Virgin Mary in the sense in which it has since been defined as an article of faith. True, he says with St. Anselm : "Purity is constituted by a recession from impurity, and therefore it is possible to find some creature purer than all the rest, namely one not contaminated by any taint of sin; such was the purity of the Blessed Virgin, who was immune from original and actual sin, yet under God, inasmuch as there was in her the potentiality of sin."[sup]74[/sup] But the "immunity from original sin" which St. Thomas ascribes to our Lady is not synonymous with "immaculate conception," as can be seen from the third part of the famous [url=https://isidore.co/aquinas/summa/TP/TP027.html#TPQ27A2THEP1][i]Summa Theologica[/i], qu. 27, art. 2[/url], ad 2. Consequently, it is not fair to charge the Angelic Doctor with inconsistency because in numerous other passages, where he treats the question [i]ex professo[/i], he denies the doctrine of the Immaculate Conception. He did not hold that God could not create a perfectly spotless creature,—his objections are mainly based on the privileged character of the Redeemer and the absolute necessity of redemption for all human beings without exception. The following passage from the [i]Summa Theologica[/i] shows that its author consistently adhered to his standpoint up to the time of his death. "If the soul of the Blessed Virgin had never been defiled by original sin, this would derogate from the dignity of Christ as the Redeemer of all mankind. It may be said, therefore, that under Christ, who as the universal Saviour needed not to be saved Himself, the Blessed Virgin enjoyed the highest measure of purity. For Christ in no wise contracted original sin, but was holy in His very conception… The Blessed Virgin, however, did contract original sin, but was cleansed therefrom before her birth."[sup]75[/sup]

This is the uniform teaching of Aquinas in all hisI writings, [i]viz.[/i]: that the birth of our Lady was holy and immaculate, but not her conception.[sup]76[/sup][hr]Notes
64. Scheeben, Schwane, [url=https://isidore.co/calibre/browse/matches/authors/1505]Chr. Pesch[/url], Többe, Gutberiet.
65. Velasquez, Sfondrati, Frassen, Lambruschini, Palmieri.
66. To this group belong Malou, Tepe, and others.
67. Prominent in this group are Cornoldi, Morgott, Hurter, etc.
68. Cfr. [i]Cur Deus Homo?[/i] II, 16.
69. "[i]Decens erat, ut ea puritate,qua sub Deo maior nequit intelligi, virgo illa niteret, cui Deus Pater unicum Filium suum, quem de corde suo æqualem sibi genitum tamquam seipsum diligebat, ita dare disponebat, ut unus idemque communis Dei Patris et Virginis esset Filius.[/i]" ([i]De Concept. Virg.[/i], c.18.)
70. "[i]Beata Virgo habuit peccatum originale, sed ante conceptionem Christi perfecte purgata est.[/i]" ([url=http://www.corpusthomisticum.org/snp3002.html#7764][i]Liber Sent.[/i], III, dist. 3.[/url])
71. Among them Albert the Great (1193-1280), who was the teacher of St. Thomas.
72. Cfr. his [url=https://isidore.co/aquinas/summa/TP/TP009.html#TPQ9A2THEP1][i]Summa Theol.[/i], 3a, qu. 9, memb. 2.[/url]
73. 73 He writes: "[i]Quidam dicere voluerunt, in anima gloriosa virginis gratiam sanctificationis prævenisse maculam peccati originalis. … Aliorum vero positio est, quod sanctificatio virginis subsecuta est originalis peccati contractionem, et hoc quia, nullus immunis fuit a culpa originalis peccati nisi solum Filius virginis: hie autem modus dicendi communior est et rationabilior et securior.[/i]" ([i]Opera S. Bonavent.[/i], t. Ill, p . 69, scholion, Quaracchi edition, 1887.)
74. "[i]Puritas intenditur per recessum a contrario, et ideo potest aliquid creatum inveniri, quo nihil purius esse potest in rebus creatis, si nulla contagione peccati inquinatum sit: et talis fuit puritas b. Virginis, quæ a peccato originali et actuali immunis fuit, tarnen sub Deo, inquantum erat in ea potentia ad peccandum.[/i]" ([url=http://www.corpusthomisticum.org/snp1042.html#3174][i]Comment. in Quatuor Libros Sent.[/i], I, dist. 44, qu. 1, art. 3[/url]).
75. "[i]Si nunquam anima b. Virginis fuisset contagio originalis peccati inquinata, hoc derogaret dignitati Christi, secundum quam est universalis omnium Salvator. Et ideo sub Christo, qui salvari non indiguit, tamquam universalis Salvator, maxima fuit b. Virginis puritas. Nam Christus nullo modo contraxit originale peccatum, sed in ipsa sui conceptione fuit sanctus. . . . Sed b. Virgo contraxit quidem originale peccatum, sed ab eo fuit mundata antequam ex utero nasceretur.[/i]" ([url=https://isidore.co/aquinas/summa/TP/TP027.html#TPQ27A2THEP1][i]Summa Theol.[/i], 3a, qu. 27, art. 2[/url], ad 2).
76. Cfr. [url=https://isidore.co/aquinas/Compendium.htm#224][i]Comp. Theol.[/i], c. 224[/url]. It is an error that the Dominican Order has always, and in almost all its distinguished men, been opposed to the pure origin of the Blessed Virgin. See Archbishop Ullathorne, [i]The Immaculate Conception[/i], ed. IIes, pp. 144 sqq. A number of Dominican theologians who wrote in favor of the Immaculate Conception are quoted by Rouard de Gard, [i]L'Ordre des Freres-Precheurs et l'Immaculee  Conception[/i], Bruxelles 1864. Cfr. also [url=https://isidore.co/calibre/browse/book/5658]Chr. Pesch, [i]Præl. Dogmat.[/i], Vol. III[/url], 3rd ed., pp. 170 sqq., Freiburg 1908; Heinrich-Gutberlet, [i]Dogmatische Theologie[/i], Vol. VII, pp. 436 sqq., Mainz 1896; W. Többe, [i]Die Stellung des hl. Thomas zu der unbefleckten Empfängnis[/i], Münster 1892; L. Janssens, [i]De Deo-Homine[/i], Vol. II, pp. 130 sqq., Freiburg 1902.
[/quote][hr][i][iurl=http://www.papalencyclicals.net/Pius09/p9ineff.htm]Ineffabilis Deus[/iurl][/i][iurl=http://www.papalencyclicals.net/Pius09/p9ineff.htm][/iurl]:

[quote]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.[/quote]