The Immaculate Conception has been a feast of the Church on December 8th for Centuries, since WAY before it was defined in the 1800s. It has been an IMPLICIT part of the Faith since Apostolic times. St Thomas Aquinas never denied this truth; he never denied that Our Lady had a special grace, or that She was sinless from birth. What was being debated was when conception occurred and when the soul was infused, which St Thomas thought was AFTER the physical cells had formed. The Church, by defining this dogma, clarified in a sense, (and in advance of the age of abortion) that life began at conception. Before that time, scientists debated when life actually happened.