What happens at communion?

Paul, writing in the 50s, passes on what he says he received: bread, "this is my body, which is broken for you. Do this in memory of me", and the cup, "this cup is the new covenant in my blood".

He adds a gloss of his own: "as often as you eat this bread and drink this cup, you proclaim the Lord’s death until he comes." The practice is older than any Gospel and older than the letter recording it.

"Unless you eat the flesh of the Son of Man and drink his blood, you don’t have life in yourselves." The hearers have already asked what a reader asks, "how can this man give us his flesh to eat?", and afterwards many of his disciples say "this is a hard saying! Who can listen to it?"

The same chapter then says "it is the spirit who gives life. The flesh profits nothing." Both sentences are in the text, and every position on this question has to do something with the one it likes less.

Justin, explaining Christian worship to an emperor: "not as common bread and common drink do we receive these", and the food "is the flesh and blood of that Jesus who was made flesh".

He is writing to persuade a hostile readership that Christians are harmless, which makes this an odd thing to volunteer. Whatever else it shows, the claim is early and it is not a later embellishment.

The Catholic catechism: "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", which "the holy Catholic Church has fittingly and properly called transubstantiation", and the presence is "truly, really, and substantially" there.

The Westminster Confession of 1646: the elements "in substance and nature, they still remain truly and only bread and wine, as they were before", and the body and blood are "not corporally or carnally, in, with, or under the bread and wine; yet, as really, but spiritually, present to the faith of believers".

There are more than two. Luther’s Small Catechism says the sacrament "is the true body and blood of our Lord Jesus Christ, under the bread and wine", and Westminster denies a presence "in, with, or under" them. The Southern Baptist confession calls the supper "a symbolic act of obedience" by which church members "memorialize the death of the Redeemer".

Westminster calls the Catholic doctrine "repugnant, not to Scripture alone, but even to common sense". The Council of Trent, whose decree the catechism quotes, says "let him be anathema" of anyone who holds that the substance of the bread remains and denies the change, and of anyone who says Christ is "only therein as in a sign, or in figure". Both are worth quoting rather than paraphrasing: this was not a polite disagreement and the documents do not pretend it was.

The saying reaches us in Greek, which has the verb. A Hebrew sentence of this shape usually does not: subject and predicate are set beside each other, in the standard grammar’s words “without a copula of any kind”. If the words were first spoken in Hebrew, they need not have contained a word for “is” at all.

So the grammatical argument does not settle it in either direction, which is inconvenient for the confident version of both positions.

Justin, writing around the middle of the second century, uses realist language with no philosophical theory attached: the bread and wine are “not as common bread and common drink”, and are “the flesh and blood of that Jesus who was made flesh”. He says what it is, and likens it to the incarnation, but gives no account of how.

Reading a later doctrine back into a sentence like that is a common move in both directions. What can be said is that a symbolic-only reading has to explain Justin, and a fully developed medieval account has to explain the absence of the machinery for several centuries.

Transubstantiation is stated in the vocabulary of substance, and it is easy to read that as one philosophy of matter among others. The Catholic Church reads it otherwise: Paul VI wrote that the council’s formulas "express concepts that are not tied to a certain specific form of human culture, or to a certain level of scientific progress, or to one or another theological school". An Orthodox synod at Jerusalem in 1672 used the word itself, and added that by it "the manner is not explained".

This is not a question evidence reaches. Nothing measurable is claimed to change, and both the strongest and the weakest accounts of what the bread is predict exactly the same bread.

That is a description of the claim, not an objection to it. It does mean the argument is about what is true rather than about what can be shown.

Traditions that disagree about what the bread is agree that the meal joins those who share it, and they say so in their own documents. Westminster, denying the sacrifice in the next sentence, still calls the supper “a bond and pledge of their communion with him, and with each other, as members of his mystical body”.

Churches out of communion with each other for nearly a thousand years also still do it, and the shape is old. Justin describes it about 155: the memoirs of the apostles or the writings of the prophets are read, the president instructs, everyone rises and prays, bread and wine mixed with water are brought, thanks are offered at length, the people answer “Amen”, and the deacons distribute. The words at the centre are older still, and Paul passes them on as something he received. That is the fact the ecumenical arguments keep returning to, and it is also why the disagreement matters as much as it does.