Ineffabilis Deus

The document was promulgated on December 8, 1854,[4] the date of the annual Solemnity of the Immaculate Conception, and followed from a positive response to the encyclical Ubi primum.

Mary's immaculate conception is a pronouncement made ex cathedra and is therefore considered by the Catholic Church to be infallible through the extraordinary magisterium.

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.

[3]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.

[6] 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.