Since the President, Mrs McAleese, received Communion in Christ Church Cathedral over a month ago, there has been a continuing flurry of comment, analysis and controversy in the media. People have been dredging up from the recesses of their memories something of what they had learned in religion lessons of yore. Highly technical terms like "transubstantiation" have been dropped into the conversation with all the menace of an unexploded bomb.

Christian optimists console themselves with the thought that in these increasingly secularist days, media-inspired controversy is the only way to get a religious topic publicly discussed. Those of a less sunny disposition murmur darkly about casting pearls before swine. Has the controversy about the Eucharist been a good or a bad thing from a Christian standpoint? Cardinal Daly plainly has his doubts.

"Sadly, some of the exchanges in recent weeks have seemed to many to be a setback to inter-church relations," he said in a sermon for Christian Unity week in Bray last Tuesday. He did not say whether he felt that inter-church relations had been seriously damaged, but he did indicate his awareness that many people felt the need to give tangible expression to their Christian fellowship with members of other traditions.

He suggested an expedient which might, he felt, meet this need. To those present at a Eucharist in a church of a different tradition he recommended a practice not uncommon in other countries. Let them approach the priest or minister with folded hands and bowed head and ask for a blessing instead of Communion.

He offers this recommendation to those "who in conscience cannot receive Holy Communion". He does not address the substantive issue of eucharistic theology nor does he address the situation of those who in conscience experience the need to share in the Eucharist of another church.

For Roman Catholics there is a law which forbids inter-communion. This is a matter of fact and record. However, Roman Catholics may find - and an increasing number do find - that receiving Communion at the Eucharist of another tradition carries deep meaning for them, and they can think of no convincing theological reason against doing so.

They therefore in conscience decide that there is a higher imperative for them than that of conforming to a law which can be changed. Only sloganeers will call this "a la carte Catholicism". If people feel constrained to use this inept phrase, then one can only say to them that every proper exercise of conscience is a la carte.

It is much more than the mere wish to show friendship to members of other churches, though this may be a valuable by-product. Rather, those who share in each other's Eucharists wish to approach the table of their common Lord and Master, conscious that they share a common faith and baptism. They recognise that there is one eucharistic faith, though there are several different and legitimate eucharistic theologies (including the Aristotelian one of transubstantiation which has been traditional for Roman Catholics).

It is quite true that the term "transubstantiation" is used in official Roman Catholic teaching documents. Therefore if someone wishes to discuss the Eucharist in terms of substance and accidents then I, as a Roman Catholic, am bound to accept that in the Eucharist the substance of the bread and wine is converted into the Body and Blood of Christ.

However, I cannot be bound to think of or discuss the Eucharist only in the language of Aristotelian philosophy. The fact is that the notions of substance and accident play little or no part in the cultures of today, and one may find it better to express one's eucharistic faith through other means. This does not mean a change in faith, only a change in the theology which expresses that faith.

It is often forgotten that the Christian Church got on perfectly well for hundreds of years without the doctrine of transubstantiation.

Since the Second Vatican Council there has been widespread recognition in the Roman Catholic Church that theology of the Eucharist has to concern itself with much more than the question of what happens to the bread and wine. Contemporary eucharistic theology is more concerned with what happens to those who participate in the eucharistic meal, at which the Scriptures are broken and digested before the bread and wine become the Body and Blood of Christ.

The claim is often made that eucharistic sharing should take place only when church unity has been achieved. One can respect this claim while remaining unconvinced by it. I cannot help reflecting that it is rather like telling sick people that they can have their medicine only after they have recovered their health.

It is easy to think of shared Eucharist only in the context of inter-church division, as if the problem and challenge of unity arises only between the churches and not within each church. All the major Christian churches experience internal stresses and strains and threats to their unity. The Roman Catholic Church used to pride itself on being an exception. It can do so no longer. When Catholics approach the altar in their own church today they might do well to reflect that though they may share a common faith, they almost certainly do not share a common theology.

Gabriel Daly, an Augustinian priest, teaches theology at Trinity College, Dublin and at the Irish School of Ecumenics