December VIII December VIII – Conception of the Blessed Virgin Mary (The Lives of the Saints – Rev. Butler) Summa Theologiae Tertia Pars – Q27 (The Sanctification of the Blessed Virgin) Ineffabilis Deus – Apostolic Constitution of the Supreme Pontiff Defining the Dogma of the Immaculate Conception (Bl. Pius IX – Dec. 8, 1854)