The first announcement of the Eucharist divided the disciples, just as the announcement of the Passion scandalized them: "This is a hard saying, who can listen to it?"(John 6:60) The Eucharist and the Cross are stumbling blocks. It is the same mystery and it never ceases to be an occasion for division. "Will you also go away?"(John 6:67):the Lord's question echoes through the ages, as a loving invitation to discover that only he has "the words of eternal life"(John 6:68) and that to receive in faith the gift of His Eucharist is to receive the Lord Himself. (Catechism of the Catholic Church, 1336)
Disclaimer: I am a layperson, not a priest. I am not theologically trained in any but the most liberal sense of the word: I have read Augustine, Thomas Aquinas, Anselm, and various other Church Fathers, but I have no more authority than anyone else in the Church.
I have always had problems with the doctrine of transubstantiation, ever since I knew what it was. After all, how can you claim that the little wafer and the bit of wine are the body and blood of Christ? Mistake me not; my question was not with the validity of the claim itself, which I can accept on faith as revealed doctrine. If you have questions about the authority of the claim, this will be of little use to you.
My questions were rather about the nature of the change. In what respect were the elements of the Eucharist the body and blood? Transubstantiation requires a change in the real substance of the bread and wine; anything else would be consubstantiation at best, a Lutheran doctrine that the Catholic Church rejects and which (as I understand it) states that the essence of Christ resides in the bread and wine, so that the elements are changed, but their essence is still present.
Here's what the Catechism of the Catholic Church has to say about transubstantiation (with some unfortunate violence to the formatting:
The mode of Christ's presence under the Eucharistic species is unique. It raises the Eucharist above all the sacraments as "the perfection of the spiritual life and the end to which all sacraments tend." (St. Thomas Aquinas, Summa Theologica III, 73, 3c) In the most blessed sacrament of the Eucharist "the body and blood, together with the soul and divinity, of our Lord Jesus Christ and, therefore, the whole Christ is truly, really, and substantially contained." (Council of Trent 1551: DS 1651) "This presence is called 'real' - by which is not intended to exclude the other types of presence as if they could not be 'real' too, but because it is presence in the fullest sense: that is to say, it is a substantial presence by which Christ, God and man, makes himself wholly and entirely present." (Paul VI, MF 39)
It is by the conversion of the bread and wine into Christ's body and blood that Christ becomes present in this sacrament. The Church Fathers strongly affirmed the faith of the Church in the efficacy of the Word of Christ and of the action of the Holy Spirit to bring about this conversion. Thus St. John Chrysostom declares:
"It is not man that causes the things offered to become the Body and Blood of Christ, but he who was crucified for us, Christ himself. The priest, in the role of Christ, pronounces these words, but their power and grace are God's. This is my body, he says. This word transforms the things offered." (St John Chrysostom, prod. Jud. 1:6: PG 49, 380)And St. Ambrose says about this conversion:
"Be convinced that this is not what nature has formed, but what the blessing has consecrated. The power of the blessing prevails over that of nature, because by the blessing nature itself is changed. ... Could not Christ's word, which can make from nothing what did not exist, change existing things into what they were not before? It is no less a feat to give things their original nature than to change their nature." (St. Ambrose, De mysteriis 9, 50;52: PL 16, 405-407)
The Council of Trent summarizes the Catholic faith by declaring: "Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread, it has always been the conviction of the Church of God, and this holy Council now declares again, that by the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation." (Council of Trent 1551:DS 1642; cf Mt 26:26 ff.; Mk 14:22 ff,; Lk 22:19ff.; 1 Cor 11:24 ff.)
Aristotle separates objects into substance and form, at least in thought. (He never makes claims that they are really thus separable, stating "The form and the matter are not separate from the thing.." in Physics Book 4 Section 2, Richard McKeon translation). He goes more fully into this in De Anima:
We are in the habit of recognizing, as one determinate kind of what is, substance, and that in several senses, (a) in the sense of matter or that which in itself is not 'a this', and (b) in the sense of form or essence, which is that precisely in virtue of which a thing is called 'a this', and thirdly (c) in the sense of that which is compounnded of both (a) and (b). Now matter is potentiality, form actuality; of the latter there are two grades related to one another as e.g. knowledge to the exercise of knowledge. (Aristotle, On the Soul, Book II Chapter 1 7-12, Richard McKeon translation)
Here we have three senses in which the above quotations about transubstantiation might be taken. Which one is correct? or rather, which one gives us the clearest understanding of the mystery?
Sense A: God's 'material', by which I don't mean He's made of stuff that could be touched, but rather His 'substrate' or 'underlying stuff', comes into the bread and wine while His 'form' doesn't. By 'form', I mean that which would be perceivable. So then, asking why we can't taste it is silly.
Thus we would say: Transubstantiation is trans-substance, not necessarily trans-form. The substance is different, but not the form, so there is nothing perceivably different about the object (which consists of both substance and form) - no difference in taste, color, texture, anything - but it still contains instead the substance of our Lord Jesus Christ. This does some violence to the original Greek conceptions, but that is a matter for faith.
This is a very pat explanation that preserves the etymology (transubstantiation not transformation) but it is wrong - counter both to dogma and reason. The distinction between being and form is one of abstraction, not one of essence. Splitting the being of God in such a way then not only flies in the face of the Church - which takes great pains to declare that it is in no way a part of God in the bread and wine, but rather He Himself wholly - but it also artificially splits being into two, thereby making a multitude out of what is properly unity.
Sense B: God's 'form' enters the bread and wine. That is, the essential element of God, that by which we say He is God, enters the bread and wine. This doesn't get us over our difficulty at first. After all, if the 'form' of God enters the bread, and it is by 'form' we perceive (e.g. we say that a statue is a statue not because it is made of bronze, but because it is statue-shaped), then why don't we perceive God in the bread? To answer this, we have to realize that 'form' can be taken in two ways. In some places, Aristotle is using the word 'morphe', which means things like physical shape, like a statue might have. In others, he uses 'eidos', which means more a purpose or definition - still tied to shape and sight, but more removed. For example, a triangle is a triangle because of its 'eidos', whereas a physical representation of a triangle has a 'morphe' that mimics the 'eidos' (well or not so well depending on who drew it, but never perfectly - 'eidos' does not admit of the imperfections necessarily present in material objects).
Furthermore, 'eidos' itself means two different things, if we look at it through the metaphor of Plato's divided line in the Republic (which I shan't quote here as being entirely too long, though I encourage you to go look at it - it starts around Republic VI 509D), where we get the (implicit?) distinction of proper objects to match the distinctions of the understanding - the lowest being the imagined things, which partake most fully of visual existence, which point through their forms to a higher realm of noetic objects, those examined in reason alone (I'm skipping over those 'believed' which exist in the mind but not examined), and then the eidetic things - the forms themselves, which transcend pure rational understanding and are those by which all other things are said to be.
These eidetic things seem very good candidates for the substance of God. They are, after all, the highest realm, and are those by which all things else are said to be. Thus we could say that the 'eidos' of God is what transubstantiates into the bread and wine, and yet while a form, thus satisfying definition (b), does not permit of perception, so we don't taste God.
However, again, this falls short. It once more splits the 'substance' of God into two parts - the essential part, and the dependent part. Then it stuffs the essential part into the bread and calls that God, which, if not heresy, is very, very close. So this won't do.
The only option left is option (c), and I think this will fit our purposes. It encompasses both (a) and (b), which we can still artificially split into the 'matter' and 'form' of God for the sake of understanding. Given what we came to above, neither present a difficulty to sense, and this allows us to address one further problem with the argument thus far.
The wording of transubstantiation is not, "This cup is the new covenant in me, poured out for you," but, "This cup is the new covenant in my blood, poured out for you." Now, after all the above, I don't mean to draw the distinction and say that only the flesh and blood of the Lord Jesus Christ become the bread and the wine, because that itself cuts off an inappropriate part from the whole. By saying flesh and blood, Christ doesn't mean a physical body made of sinews and meat and such. If he did, the original Supper would have promptly done so, given His power, and I'm sure the Gospels would have mentioned it (and the Apostles would have balked, excepting maybe Peter). The only way that I can make sense of it is if He meant that the substance of His flesh and blood - meaning their whole reality as the flesh and blood of God per se. That is, He doesn't mean the specific corporeal body He has - or perhaps He does, but not understood like a butcher understands the body of a lamb, as material for other designs. The body is, in a metaphor that reveals itself as metaphor and in so doing reveals itself as truth beyond the metaphor, present to us, as full substance - the 'material' of God and the 'form' of God united in the 'being' of God, but both (which is truly one), not being proper objects of sense, not perceivable in the communion wafer or the communion wine, to fall back on the metaphor through which the understanding grasps at such high objects.
This is still a mystery, but the point of this inquiry was not and could not be to solve the mystery, but rather to cast it in the light of what understanding I could bring to it.