The Immaculate Conception is, according to Roman Catholic dogma, the conception of Mary, the mother of Jesus without any stain of original sin, in her mother's womb: the dogma thus says that, from the first moment of her existence, she was preserved by God from the lack of sanctifying grace that afflicts mankind, and that she was instead filled with divine grace. It is further believed that she lived a life completely free from sin. Her immaculate conception in the womb of her mother, by normal sexual intercourse (Christian tradition identifies her parents as Sts. Joachim and Anne), should not be confused with the doctrine of the virginal conception of her son Jesus. The feast of the Immaculate Conception, celebrated on December 8, was established as a universal feast in 1476 by Pope Sixtus IV. He did not define the doctrine as a dogma, thus leaving Roman Catholics freedom to believe in it or not without being accused of heresy; this freedom was reiterated by the Council of Trent. The existence of the feast was a strong indication of the Church's belief in the Immaculate Conception, even before its 19th century definition as a dogma. Now, the Roman Catholic tradition has a well established philosophy for the study of Immaculate Conception and the veneration of the Blessed Virgin Mary via the field of Mariology with Pontifical schools such as the Marianum specifically devoted to this task.