In 1854 Pope Pius IX defined the doctrine of the Immaculate Conception:

Wherefore, in humility and fasting, we unceasingly offered our private prayers as well as the public prayers of the Church to God the Father through his Son, that he would deign to direct and strengthen our mind by the power of the Holy Spirit. In like manner did we implore the help of the entire heavenly host as we ardently invoked the Paraclete. Accordingly, by the inspiration of the Holy Spirit, for the honor of the Holy and undivided Trinity, for the glory and adornment of the Virgin Mother of God, for the exaltation of the Catholic Faith, and for the furtherance of the Catholic religion, by the authority of Jesus Christ our Lord, of the Blessed Apostles Peter and Paul, and by our own: “We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instant 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.”

Hence, if anyone shall dare — which God forbid! — to think otherwise than as has been defined by us, let him know and understand that he is condemned by his own judgment; that he has suffered shipwreck in the faith; that he has separated from the unity of the Church; and that, furthermore, by his own action he incurs the penalties established by law if he should dare to express in words or writing or by any other outward means the errors he think in his heart.

This doctrine was believed and celebrated in the Church long before this definition, and it would be seriously misleading to suppose that the definition represented any meaningful change in the general beliefs of Catholics. However, not all Catholics always held it, and St. Thomas in fact did not accept it:

I answer that, The sanctification of the Blessed Virgin cannot be understood as having taken place before animation, for two reasons. First, because the sanctification of which we are speaking, is nothing but the cleansing from original sin: for sanctification is a “perfect cleansing,” as Dionysius says (Div. Nom. xii). Now sin cannot be taken away except by grace, the subject of which is the rational creature alone. Therefore before the infusion of the rational soul, the Blessed Virgin was not sanctified.

Secondly, because, since the rational creature alone can be the subject of sin; before the infusion of the rational soul, the offspring conceived is not liable to sin. And thus, in whatever manner the Blessed Virgin would have been sanctified before animation, she could never have incurred the stain of original sin: and thus she would not have needed redemption and salvation which is by Christ, of whom it is written (Matthew 1:21): “He shall save His people from their sins.” But this is unfitting, through implying that Christ is not the “Saviour of all men,” as He is called (1 Timothy 4:10). It remains, therefore, that the Blessed Virgin was sanctified after animation.

Responding to the objection that in some places the feast of Mary’s Conception was already being celebrated, he says:

Although the Church of Rome does not celebrate the Conception of the Blessed Virgin, yet it tolerates the custom of certain churches that do keep that feast, wherefore this is not to be entirely reprobated. Nevertheless the celebration of this feast does not give us to understand that she was holy in her conception. But since it is not known when she was sanctified, the feast of her Sanctification, rather than the feast of her Conception, is kept on the day of her conception.

This is an unfair description of the feast, as those who wished to celebrate Mary’s conception in fact believed that she was sanctified in the first moment, even though St. Thomas denies it. And in this sense it is clear that there was in fact significant historical continuity. However, the suggestion, implied by the words of Brownson, even though elsewhere he admits it to be untrue, that all Catholics of good will have always believed all the doctrines accepted by the Church of the nineteenth century, simply cannot be maintained.