And with Mark of Minute Particulars, who quoted the Pope as saying the dogmatic definition of the Immaculate Conception "prescinds from all explanations about how the soul is infused into the body and attributes to the person of Mary, at the first moment of her conception, the fact of her being preserved from every stain of original sin."
Which means I disagree, somewhat, with my previous agreement with the old Catholic Encyclopedia, which stated, "The term conception [in the definition] does not mean the active or generative conception by her parents."
Well before the doctrine of the Immaculate Conception gained much attention, the Church was keeping the Feast of the Conception of Mary. A conception is something people naturally understand, just as they understand a birth and a death. Conception is the beginning of a life made public by birth and ended by death. These are events humans naturally think in terms of.
An infusion of a soul into a body... that's a bit too philosophical to get dressed up and go to church for. If there ever was a Feast of Somebody or Other Attaining the Age of Reason, it hasn't survived in the reason-loving West.
I do still agree with this statement from the Encyclopedia: "The person is truly conceived when the soul is created and infused into the body." So I still don't think the definition of the Immaculate Conception necessarily implies the soul is infused into the body at biological conception (although I think other things do necessarily imply that). Rather, I think it means that there was never any being that could be said to be, or on its way to becoming, Mary that was not preserved from every stain of original sin.
Well, so what? So I'm now formulating a principle to look for and expect a "natural human" expression or development in even the more philosophical and theological aspects of Catholicism.