Today, the feast of the Conception of the Blessed Virgin Mary, is an ancient feast in the Eastern Churches, but a fairly new one in the Latin world. The Greek churches observe this feast under the name Maternity of St. Anne on December 9th, while the Roman Church, before 1570 and since Pius IX, has called it the Immaculate Conception.
The Immaculate Conception is a remarkable doctrine that could only have crystallized under Scholasticism, even though Latin Scholasticism failed to do so. It was Western medieval thinking under Scotus, although not Aquinas' intellectual tradition, that provided a vocabulary to talk about something intuitively believed since ancient times. If Scholasticism is strictly limited to the tradition of St. Thomas Aquinas, then the Western Scholastics got the Immaculate Conception wrong, but the Angelic Doctor's self-professed biggest fan, George Gennadios Scholarios (first post-Byzantine patriarch of the Greek Church), got right.
In the years since 1453 the Orthodox Church has embraced mysticism as its perspective and Greek patristics as its creed, but much has changed since the fall of Constantinople, not the least of which is the closing of discussion to other manners of theology, a shame for a Church that had such a varied tradition (the Cappadocian Fathers, St. Symeon, Palamas, and the Greek Scholastics). There was a time when, despite arguments about how thick bread should be or whether a word in Latin was as heretical as it was in Greek, a mutually influential discussion could still transpire about the Mother of God. Christiaan Kappes, a rare Catholic priest with original thoughts, has given an interview plugging his book on the Immaculate Conception and its roots in Greek theology. Brush up on your Byzantine thought here (although I am not generally a fan of that blog).
A happy feast to all!