« INEFFABILIS DEUS ». — With these words begins the apostolic letter (dogmatic bull) by which Pius IX defined, on 8 December 1854, Immaculate Conception (v.).
The distinguished document, the fruit of the long and diligent studies of the theological commission established by the Pope, sets forth with clarity and warmth the reasons that led the Church to the solemn definition. Because of the intimate solidarity existing among all parts of Mariology, the bull I. D. recalls principles and advances affirmations of great value and significance concerning the predestination of the Virgin, her impeccability, the mediation of all graces, and Mary’s association in the work of salvation.
BIBL.: X. Le Bachelet, Immaculée Conception, in DThC, VII, cols. 1195–1214 (history of the preparation of the bull); A. Tundini, Le encicliche mariane, Rome 1950, pp. 29–57 (Latin text of the bull with Italian translation).