In another thread, Anne posted a passage from Ignatius of Antioch that Roman Catholics often cite in support of their view of the eucharist. I thought I'd repeat and expand upon my response to Anne here, since some people might find it helpful. In my experience, this passage from Ignatius is one of the most commonly cited patristic passages among Roman Catholics.
Here's the passage:
"They abstain from the Eucharist and from prayer, because they confess not the Eucharist to be the flesh of our Saviour Jesus Christ, which suffered for our sins, and which the Father, of His goodness, raised up again." (Letter To The Smyrnaeans, 7)
Yet, earlier in the same letter Ignatius writes:
"Yea, far be it from me to make any mention of them, until they repent and return to a true belief in Christ's passion, which is our resurrection." (5)
Are we to conclude that Ignatius believed that Jesus' passion (or faith in His passion) is transubstantiated into our resurrection under the appearance of remaining Jesus' passion (or faith in His passion)?
Ignatius often wrote in a manner similar to what we see in the two passages quoted above. That should be a signal to the careful interpreter to proceed with caution.
There's nothing in Ignatius that tells us much about his view of the eucharist. Catholics can't claim to know that Ignatius agreed with them on this issue.
This passage in Ignatius was written in response to heretics who deny the physicality of Christ. Any of the popular views of the eucharist, including the symbolic view, would contradict the denial of Christ's physicality that Ignatius was arguing against. The symbolic view maintains that the eucharist has reference to Christ's physical body, so both a Baptist who holds the symbolic view and a Roman Catholic who adheres to transubstantation could agree with what Ignatius wrote. While it's possible that Ignatius believed in some sort of physical presence in the eucharist, nothing in the passage in question tells us that he did. When Jesus says that the cup is the new covenant (Luke 22:20), He obviously doesn't mean that the cup is transubstantiated into the new covenant. A covenant isn't something physical, and surely all of us understand how Jesus could use "is" in some sense other than transubstantiation. The same is true of Ignatius. Whether the eucharist represents Christ's physicality or is transubstantiated into it, either view contradicts a denial of Christ's physicality.
Roman Catholics often assume transubstantiation or something similar to it whenever they see an opportunity to read such a concept into a text. I would suggest that people closely examine Catholic claims on this subject, because a lot of what's commonly asserted is incorrect. A "real presence" isn't equivalent to transubstantiation. A person can believe in some type of eucharistic presence without believing in the Roman Catholic view of the eucharist. Many church fathers held a view of the eucharist that contradicts the Catholic view or could plausibly be interpreted in more than one way, not just in a Roman Catholic sense.
A good online source on this subject is Philip Schaff's church history. See section 69 here and section 95 here. I also recommend consulting Schaff's notes, since the notes cite additional passages from the fathers and cite other scholars confirming Schaff's conclusions. I don't agree with Schaff on every issue, and he doesn't include some arguments I would include, but his church history is good for a general introduction to the subject.
Contrast what Schaff and other scholars have documented with claims like these made by the Council of Trent:
"our Redeemer instituted this so admirable a sacrament at the last supper, when, after the blessing of the bread and wine, He testified, in express and clear words, that He gave them His own very Body, and His own Blood; words which, - recorded by the holy Evangelists, and afterwards repeated by Saint Paul, whereas they carry with them that proper and most manifest meaning in which they were understood by the Fathers, - it is indeed a crime the most unworthy that they should be wrested, by certain contentions and wicked men, to fictitious and imaginary tropes, whereby the verity of the flesh and blood of Christ is denied, contrary to the universal sense of the Church, which, as the pillar and ground of truth, has detested, as satanical, these inventions devised by impious men" (session 13, chapter 1, "On the real presence of our Lord Jesus Christ in the most holy sacrament of the Eucharist.")
"Since Christ our Redeemer said that that which he offered under the appearance of bread was truly his body, it has therefore always been held in the Church of God, and this holy Synod now declares anew, that through consecration of the bread and wine there comes about a conversion of the whole substance of the bread into the substance of the body of Christ our Lord, and of the whole substance of the wine into the substance of his blood. And this conversion is by the Holy Catholic church conveniently and properly called transubstantiation." (session 13, chapter 4, "Decrees Concerning the Most Holy Sacrament of the Eucharist")