Ineffabilis Deus

During the reign of his predecessor, Pope Gregory XVI, the bishops in various countries began to press for a definition as dogma of the teaching of Mary’s immaculate conception.[6] Pius then appointed a commission to study the matter; in 1849, in the encyclical Ubi primum, he solicited the opinions of the bishops.

Pius takes note that Early Church Fathers, such as Irenaeus, compared Eve and Mary.

Hence, to demonstrate the original innocence and sanctity of the Mother of God, not only did they frequently compare her to Eve while yet a virgin, while yet innocence, while yet incorrupt, while not yet deceived by the deadly snares of the most treacherous serpent; but they have also exalted her above Eve with a wonderful variety of expressions.[3]

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Mariology of the Catholic Church
Virgo by Josef Moroder-Lusenberg
Overview Prayers Antiphons Hymns to Mary Devotional practices Saints Societies Consecrations and entrustments Veneration
Prayers Angelus As a Child I Loved You Fátima prayers Flos Carmeli Hail Mary Hail Mary of Gold Immaculata prayer Magnificat Mary, Mother of Grace Mary Our Queen Memorare Sub tuum praesidium
Antiphons Alma Redemptoris Mater Ave maris stella Ave Regina caelorum Salve Regina
Hymns to Mary Hail Queen of Heaven, the Ocean Star Immaculate Mary Avé de Fátima Lo, How a Rose E'er Blooming O sanctissima Regina Caeli Stabat Mater
Devotional practices Acts of Reparation Consecration to Mary First Saturdays Rosary Seven Joys of the Virgin Seven Sorrows of Mary Three Hail Marys
Movements and societies Sodality of Our Lady Congregation of Marian Fathers Company of Mary (Montfort) Marianists (Society of Mary) Marist Fathers Marist Brothers Schoenstatt Movement Legion of Mary World Apostolate of Fátima (Blue Army) Mariological Society Our Lady's Rosary Makers Marian Movement of Priests Fatima Family Apostolate Queen of Angels Foundation
Apparitions Approved by the Pope Aparecida Banneux Beauraing Fátima Guadalupe La Salette Laus Lourdes Miraculous Medal Pontmain
Key Marian feast days Mother of God (1 January) Annunciation (25 March) Assumption (15 August) Immaculate Conception (8 December)
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The decree surveys the history of the belief in Christian tradition, citing its roots in the long-standing feast of the Conception of Mary as a date of significance in the Eastern and Western churches. It also cites the approval of Catholic bishops worldwide who were asked in 1849 to offer their opinion on the matter.[7]

The dogmatic statement is expressed near the end of the document:

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.[8]

"Mary's privilege ... was the result of God's grace and not of any intrinsic merit on her part",[9] which is reflected in the decree. In this Pius followed the reasoning of John Duns Scotus.[10] "The Perfect Redeemer, must in some case, have done the work of redemption most perfectly, which would not be, unless there is some person, at least, in whose regard, the wrath of God was anticipated and not merely appeased."[11] The 1964 Dogmatic Constitution, Lumen gentium noted the view prevalent "...among the Fathers whereby they called the mother of God entirely holy and free from all stain of sin, as though fashioned by the Holy Spirit and formed as a new creature."[12]

• Immaculate Conception
• Marian papal encyclicals and Apostolic Letters
• Papal infallibility

• Complete text of the decree