I have just opened a thread at this subforum titled "Description of transubstantiation in terms of hylomorphic theory" that may help you understand this mistery. To note, the thesis I am proposing goes beyond the dogma of transubstantiation yet, at least IMV, is wholly compatible with it, just as understanding the Hypostatic Union as the divine Person of the Son being the Act of Being of Jesus' human nature goes beyond Chalcedonian dogma yet is wholly compatible with it.

Regarding your last question, which is not addressed in my thesis, I will just say that Jesus' humanity is the instrument, the "sacrament", of his divinity. We partake physically of his body in order to partake spiritually of his divinity (2 Pe 1:4).

BTW, this doctrine is held not just by Catholics but also by the Eastern Orthodox. They just do not use the word "transubstantiation" because it assumes the Aristotelian categories of substance and accidents, and they seem to prefer not to use Aristotelian concepts. They just say that the bread is changed into the body of Christ.

Last edited by Johannes (7/17/2015 5:06 am)

Jesus' humanity is the instrument, the "sacrament", of his divinity. We partake physically of his body in order to partake spiritually of his divinity (2 Pe 1:4).

What does it mean for humanity to be an insturment of divinity? And why is it necessary to partake physically to partake spiritually? 

What somewhat astounds me is that the doctrine of Mary's perpetual virginity (MPV for short) is the number 1 most confusing Catholic doctrine to you; are really telling me that neither, say, Mary's Assumption or Immaculate Conception don't harbor any equal or greater difficulties to you?

I mean, comparatively, MPV has much more going for it on Protestant premises; it has greater support in the Father's than practically any other doctrine, even Christ's divinity. I know a number of modern Protestant commentators have accepted it on a grammatical-historical evaluation of the Bible's text alone. Luther accepted it; I've heard in fact that it was part of the Augsburg Confession. Also, practically every English divine who put pen to paper until around the 1800's accepted it. (And no, John Wesley was no exception; in fact, it, technically, is still Methodist teaching to this day) Even John Calvin thought it to be at least to be most probably true, even if he wasn't decided in favor of it himself (the evidence is ambiguous).

So, back to the point; can you explain why to me, exactly, MPV is such a stumbling block to you, especially compared to something like the Immaculate Conception?

You seemed genuinely astounded by my unbelief  To answer your question though: What do these theologians have to do with me? I'm sure they did accept it, but that doesn't make it any more understandable to me.

Mary's Assumption makes sense: If God wanted to, why not bring his mother to heaven directly at the end of her life? Not at all implausible. The immaculate conception is reasonable too; if God could make Christ without sin, why not the mother of Christ (though it's a little more theologically tricky since Mary would then be saved by a grace other than that of the cross)? No big deal. I don't think I believe them, but I think if submitted to the authority of the Catholic church I could get behind them with little issue.

The problem I have with MPV is that it seems to flatly contradict Catholic teaching. In sexual ethics, Catholics have always taught that the procreative element of marriage is fundamental to it; there can be no homosexual marriage because there can be no homosexual procreation. It is for this reason marriages that were never consummated can be ended with an anullment rather than by divorce. Apart from sex there simply is no marriage. How then could Mary and Joseph possibily be married by Catholic standards? Not only does that go against the sexual ethic Catholics champion, it goes against the teachings of their own saint who wrote in the Bible that a husband and wife should not deprive their bodies from one another except only for a brief time. 

Last edited by Mark (7/17/2015 12:10 pm)

Not quite. If the substance changes, the substantial form must change. It's the accidents, not the forms*, that remain unchanged.

Woops, you're right, that was a slip. I meant "form" there in the non-philosophical sense: physical apperance. 

Bear in mind too that the Eucharist is officially a mystery

That seems reasonable to me, but then I suppose I wonder why Catholic dogma insists pretty to know precisely what it means. I once asked a well-educated protestant why he disbelieved in transubstantiation, and he said that it was because the doctrine is too specific; he did not know what it meant for the bread to be the body, but for that exact reason he made no specific claims about knowing what it meant. Catholics on the other hand not only make very detailed claims about what happens in the Eucharist, but they insist that belief in those claims are central to the faith (dogma). So I guess I'm unconvinced by claims of mystery.

Belief in the Real Presence is a gift of faith, not one at which we can arrive through unaided natural reason.

I worry that this undermines our ability to know the world we live in. If bread can be be God in substance, can other objects be completely different substancesunbknownst to us? It oddly opens the door to the claims of the skeptics.

because in the conversation described in John 6 Jesus commanded us to do so as a vehicle of sanctifying grace

Does Catholic theology contain an explanation for this command? That is, how it goes about providing sanctification? 

"Understanding the Eucharist" Dr. Scott Hahn (Audio) (Youtube)
Part 1 of 3
Part 2 of 3
Part 3 of 3
 

Johannes wrote:

BTW, this doctrine is held not just by Catholics but also by the Eastern Orthodox. They just do not use the word "transubstantiation" because it assumes the Aristotelian categories of substance and accidents, and they seem to prefer not to use Aristotelian concepts. They just say that the bread is changed into the body of Christ.

In a certain snese, this is one issue that is somehow indicative (in a very general way) of the ways that Orthodox, Catholics, and Protestants approach things.  Protestants tend to hold Christ's words to be symbolic (which has always struck me as bizarre, since they are usually the ones obsessed with LITERALISM).  Catholics accept the real presence and put forward a plausible metaphysical account of HOW bread and wine can both BE the body and blood of Christ AND at the same time still have all the properites, even the essential properties, of bread and wine.   Orthodox accept the real presence, because Christ says this is his body and blood.  If you ask us how this is possible metaphysically, we Orthodox tend to say, "We don't know.  We are told to participate in and live this mystery, not to understanding it metaphysically."   

I am not in no way opposed to metaphysics or theology, but I am convinced that good theology requires holiness, and holiness always manifests a certain humility of reason before the divine mysterion.  

For example, my copy of the Summa Theologiae has written on it in big fat black Sharpie letters:  STRAW  
I think that's worth remembering every time one reads Thomas.