It’s important to understand what the doctrine of the Immaculate Conception is and what it is not. Some people think the term refers to Christ’s conception in Mary’s womb without the intervention of a human father; but that is the Virgin Birth. Others think the Immaculate Conception means Mary was conceived “by the power of the Holy Spirit,” in the way Jesus was, but that, too, is incorrect. The Immaculate Conception means that Mary, whose conception was brought about the normal way, was conceived without original sin or its stain—that’s what “immaculate” means: without stain. The essence of original sin consists in the deprivation of sanctifying grace, and its stain is a corrupt nature. Mary was preserved from these defects by God’s grace; from the first instant of her existence she was in the state of sanctifying grace and was free from the corrupt nature original sin brings.
Although the belief was widely held since at least Late Antiquity, the doctrine was not formally proclaimed until December 8, 1854, by Pope Pius IX in his papal bull Ineffabilis Deus. There he proclaimed that the Immaculate Conception is a dogma of the Catholic Church maintaining that from the moment when she was conceived the Blessed Virgin Mary was kept free of original sin and was filled with the sanctifying grace normally conferred during baptism.
The Forerunners: Celebration of the Feast of the Conception of Mary. A feast of the Conception of the Most Holy and All Pure Mother of God was celebrated in Syria on 8 December perhaps as early as the 5th century. By the 7th century the feast of her conception was widely celebrated in the East, under the name of the Conception of Saint Anne – St Anne being Mary’s mother. In the West it was known as the feast of the Conception of Mary, and was associated particularly France and England. By the 11th century Eastern Orthodox icons appeared of the Theotokos Panachranta, i.e. the “all immaculate” Mary. Note that the title of achrantos (spotless, immaculate, all-pure) refers to the holiness of Mary, not specifically to the holiness of her conception.
The Medieval Theological Debates. The spread of the feast, by now with the adjective “Immaculate” attached to its title, met opposition on the part of medieval philosophers and theologians, notably including Saints Bernard of Clairvaux, Albertus Magnus and Thomas Aquinas. Among the principal defenders of the expression “Immaculate Conception” were the Franciscans, most notably John Duns Scotus.
Saint Thomas Aquinas opposed the idea of the Immaculate Conception on the ground that unless the Blessed Virgin had at one time or other been one of the sinful, she could not justly be said to have been redeemed by Christ. The Franciscan, St. Bonaventure, second only to Saint Thomas in his influence on the Christian schools of his era, hesitated to accept it for a similar reason. He believed that Mary was completely free from sin, but that she was not given this grace at the instant of her conception.
John Duns Scotus proposed a solution to the theological problem of reconciling the doctrine with that of universal redemption in Christ, when he argued that Mary’s immaculate conception did not remove her from redemption by Christ; rather it was the result of a more perfect redemption granted her because of her special role in salvation history.
The Beginning of Recognition of what the Church had long celebrated. Popular opinion remained firmly behind the celebration of Mary’s conception. In 1439, the Council of Basel, which is not reckoned an ecumenical council, stated that belief in the immaculate conception of Mary is in accord with the Catholic faith.
On 28 February 1476, Pope Sixtus IV, a Franciscan after whom the Sistine Chapel is named, authorized those dioceses that wished to introduce the feast to do so, and introduced it to his own diocese of Rome in 1477. With his bull Cum praeexcelsa of 28 February 1477, in which he referred to the feast as that of the Conception of Mary, without using the word “Immaculate”, he granted indulgences to those who would participate in the specially composed Mass or Office on the feast itself or during its octave, and he used the word “immaculate” of Mary, but applied instead the adjective “miraculous” to her conception.
On 4 September 1483, referring to the feast as that of “the Conception of Immaculate Mary ever Virgin”, he condemned those who argued about the specific declaration whether the Virgin Mary was conceived without the stain of original sin, saying “up to this time there has been no decision made by the Roman Church and the Apostolic See.” This decree was reaffirmed by the Council of Trent.
The feast was celebrated in various ways and in various places, but in 1708, Pope Clement XI made the feast of the Conception of Mary a holy day of obligation.
Definition of the dogma. During the reign of Pope Gregory XVI the bishops in various countries began to press for a definition as dogma of the teaching of Mary’s immaculate conception. Pius IX appointed commissions to investigate the whole subject, and he was advised in 1851 that the doctrine was one which could be defined and that the time for a definition was opportune.
It was not until 1854 that Pope Pius IX, with the support of the overwhelming majority of Roman Catholic bishops, whom he had consulted between 1851–1853 (via the encyclical Ubi primum), promulgated the papal bull Ineffabilis Deus (Latin for “Ineffable God”), which defined ex cathedra the dogma of the Immaculate Conception. What is important to note is that the bishops widely consulted the faithful to see what they held to be true. In this sense the dogma of the Immaculate Conception defined by Pope Pius IX is also viewed as a key example of the use of sensus fidelium shared by believers and the Magisterium rather than pure reliance on Scripture and Tradition
On 8 December 1854, in a great assembly of bishops in St Peter’s Basilica at Rome, he promulgated the document Ineffabilis Deus, in which the history of the doctrine is summarily traced, and the proclamation:
We declare, pronounce and define that the doctrine which holds that the Blessed Virgin Mary, at the first instant of her conception, by a singular privilege and grace of the Omnipotent God, in virtue of the merits of Jesus Christ, the Savior of mankind, was preserved immaculate from all stain of original sin, has been revealed by God, and therefore should firmly and constantly be believed by all the faithful.
The papal definition of the dogma declares with absolute certainty and authority that Mary possessed sanctifying grace from the first instant of her existence and was free from the lack of grace caused by the original sin at the beginning of human history. Mary’s salvation was won by her son Jesus Christ through his passion, death, and resurrection and was not due to her own merits.