This month, as the culmination of the “Year of the Eucharist” designated by the late John Paul II, Catholic bishops from around the world will gather for a synod in Rome to explore and deepen the church’s understanding of this sacrament.

As older Catholics know, but many young Catholics do not, transubstantiation is the doctrine that the “substance” of the bread and wine in the Eucharist is changed into the body and blood of the risen Christ, while the appearance of bread and wine remains. This traditional doctrine of the church is stated in the Catechism of the Catholic Church (1376): “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 whole substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation.” This language closely follows that of the Council of Trent, which in turn closely followed Aquinas.

Transubstantiation has always been a difficult doctrine to explain and to understand. Trent said that the “appearance” or “form” (in Latin, species) of the bread and wine remains. Aquinas, following Aristotelian philosophy and physics, said that the “accidents” (that is, the appearance) remained, while the “substance” was converted into the body and blood of the risen Christ. But in Aristotelian physics, there is no such thing as a free-standing “accident.” An accident, like the color red, must be a quality of, or inhere in, some substance. Aquinas knew this, yet held that the accidents or appearances of the bread and wine, after consecration, did not inhere in any subject, but were held in being by a continuous miracle. Using Trent’s language, we would have to say that the appearance or form of the bread and wine remains, but does not inhere in any subject. Luther found transubstantiation impossible to believe, and so taught that the bread and wine remained real substances after the consecration, but that the substance of Christ’s body was also present.

The doctrine of transubstantiation has not become easier to believe with time. A 1993 Gallup poll revealed that only 30 percent of American Catholics believe that they are actually receiving the body and blood of Christ when they receive Communion. Many Catholics, especially the young, like their Protestant brethren, see the Eucharist as a symbol, in the weak sense, rather than the real presence of the body and blood of Christ.

Part of the problem is theological. After Vatican II, attempts to explain transubstantiation in metaphysical terms came to be seen as problematic, and were largely replaced by another approach, called “transignification”: the idea that the eucharistic ritual changes the meaning (or significance) of the bread and wine. Since the meaning of a thing is part of its reality for us, insofar as the meaning of the bread and wine is changed, the bread and wine themselves are changed. Liturgist James White put it this way: “The concept of Christ’s presence in the Eucharist has acquired the name ‘transignification.’ Christ uses bread and wine...to give himself to us. No longer is it accurate to say that the elements are merely bread and wine. They are a gift; the reality of them completely changes because they become means through which we experience anew Jesus Christ.”

Transignification, then, focuses on the change in the perception of the Eucharist, rather than focusing on any ontological or metaphysical change in the eucharistic elements themselves. Its strength is that it sees the eucharistic transformation as involving the whole congregation. Its weakness is that it minimizes or neglects any ontological change in the eucharistic elements. To use White’s example, if I give a gift of bread to my neighbor, its reality does not “completely change.” If it did, it would no longer be bread, or even a gift.

Transignification was a response to serious theological problems with the traditional metaphysical understanding of transubstantiation. These centered on what was meant by “substance.” “Substance” can mean that which makes a thing what it is, its essential and innermost reality, or that which supports (the Latin root means “stands under”) the “accidents” of a thing. Now, in a scientific analysis, what makes bread and wine what they are, their essential reality, is their chemical and molecular composition. To take a simple example, the molecular formula of ethyl alcohol (a component of wine) is CH3CH2OH: two atoms of carbon surrounded by hydrogen atoms and joined to a hydroxide (OH) radical. But the very same atoms, rearranged, make diethyl ether (CH3OCH3)-a different substance, with different properties from ethyl alcohol. So, in a modern perspective, it is the chemical structure (not just the atoms) that makes a substance what it is, its essential reality.

This points up the problem with a substance analysis of the elements. No one claims that the bread and wine, after the consecration, are chemically and physically different from what they were before the consecration. So how can we say that the “substance” of these elements has changed in the eucharistic ceremony? We would have to locate this change in some substrate which “stands under” the chemical structure and is unreachable by scientific analysis. That was the position taken by metaphysical analysts before the advent of transignification, but it suffered from several problems. First, it is not clear what it means. Cyril Vollert, in his article “Transubstantiation” (New Catholic Encyclopedia, 1967 and 2004 editions) writes: “In transubstantiation the protons, neutrons, electrons, atoms, molecules, etc., that is, the entire agglomeration of substances constituting the bread and wine, are converted into the body and blood of Christ.” Does this mean that the molecules of the bread and wine become the molecules of Christ’s body and blood? It is not clear. Second, as noted above, following Aquinas, the “accidents” or appearances of the bread and wine are not thought of as accidents of Christ’s body and blood; rather, they are free-floating appearances, grounded in no substance at all, but sustained miraculously. But this does not make sense, and has no analogy in nature. It is like talking about hardness without matter, or color without light. Even a miracle cannot accomplish the impossible; miracles elevate and perfect nature, they do not contradict it (see my “Miracles in Science and Theology,” Zygon, September 2002). Finally, the church, following the Council of Trent (see Denzinger-Schonmetzer, no. 1652), teaches that the consecrated elements are no longer bread and wine at all, but are wholly the body and blood of the risen Christ; nothing of the bread and wine remains. This seems incredible.

While not rejecting the language of transignification, which complements transubstantiation, I wish to suggest another way of understanding transubstantiation. While still metaphysical, it offers a more coherent, intelligible, and therefore more credible conception of this mysterious conversion.

Aquinas argued that there can be only one substance in a unified body, like an organism. I have argued elsewhere (“Aquinas’s Concept of Substantial Form and Modern Science,” International Philosophical Quarterly, September 1996) that Aquinas’s thought could be creatively completed by the notion of subsidiary form; that is, a form which is not an accident but also is not a substance, because it does not exist independently. Examples might be a molecule of protein, a blood cell, or the heart, existing in a human body. These have their own formal unity-a unity of both properties and action. They also exist within a larger substance-a body-and cannot exist by themselves apart from it. They are not substances themselves, because they do not exist independently, but exist in another. They can, though, be transplanted into another body, and they can be kept alive in vitro for some period of time, indicating that they are not merely “accidents.” They are neither substances nor accidents, then, but subsidiary entities, which have their own formal unity, but exist within another substance, the body.

My proposal is that we think of the consecrated elements of the Eucharist analogically as subsidiary entities. The substances of the bread and wine after consecration are incorporated into a larger substance, the risen and glorified body of Jesus. Hence they cease to be separate, independent substances. Not their chemical composition, but their whole mode of existence has changed. They exist no longer in themselves-as natural substances-but have been ingrafted into and exist entirely within another substance, the glorified body of Christ. Therefore, they can be said to be transubstantiated. Yet their chemical constitution remains the same. What they cease to be is independent substances. Their natural mode of existence has been entirely taken up into the supernatural reality of the glorified Christ. Therefore they can be said truly to be the body and blood of Christ, and no longer what we normally mean by bread or wine, since in common parlance bread and wine refer to natural substances that are not a part of any other substance.

Now, this incorporation must be understood as an analogy. The natural analogue is the incorporation of a substance, for example a protein molecule, into a body after ingestion. The analogous referent is the incorporation of the substance of the bread and wine into the substance of the glorified body and blood of Christ. This takes place at the level of existence, what Aquinas refers to as esse. It is the esse (the very existence) of the bread and wine that is ingrafted into the esse of the risen Christ, while the natural properties of the bread and wine remain what they were. In fact, anything said about the glorified body-it is free, spiritual, imperishable (see 1 Cor 15)-is analogous. We are taking terms from a natural human context, stripping them of their human limitations, extrapolating their meaning, and applying them to a supernatural reality.

This understanding of transubstantiation, as a mode of incorporation, parallels what actually happens to believers in heaven and in the eucharistic celebration. For we say that the saints are incorporated into the body of Christ, yet they remain who they are; their individual human personalities are not extinguished. But in the traditional understanding of transubstantiation, the substance of the bread and wine is wholly changed into the body and blood of Christ-nothing of the bread and wine remains. This therefore is not a sign of what happens to believers when they are incorporated into the body of Christ; it is a counter-sign. For, if we thought of believers being “transubstantiated” (in the traditional understanding of that term) into the body of Christ, we would have to say that their human reality and personality were transformed into that of Christ and did not remain. Rather than being united with Christ, they would literally become Christ. And no Christian wants to say this. One important advantage, then, to the interpretation I am offering is that transubstantiation can be understood as a sign and a parallel of the incorporation of believers into the body of Christ.

Modern commentators speak of the Eucharist as a meal of fellowship, in which Christ gives himself to us and makes himself present. In the traditional understanding of transubstantiation, however, it is hard to see how the Eucharist can be a meal. What exactly are we eating? It is not the bread and wine, since after the consecration they are no more. Certainly it is not the literal, physical, flesh and blood of Jesus, which would make us cannibals (I cannot think of a faster way to empty the churches than to emphasize this interpretation). Therefore we are eating the glorified body and blood of Christ. But these are spiritualized matter, not physical in the way that bread and wine are physical, so it is hard to see how they constitute a meal.

Again, as noted above, the traditional understanding of transubstantiation has no analogy in nature and is therefore difficult to understand and to believe. The accidents or appearances of bread and wine are said to remain but to inhere in no substance. To help overcome this impasse, it may help to reflect on Jesus’ Resurrection. In the Resurrection, the supreme miracle, the natural body of Jesus does not cease to exist but is transformed into an apparently different kind of materiality, although recognizably the same body. There is therefore continuity and discontinuity, whereas in transubstantiantion, as traditionally conceived, there is no continuity, only discontinuity. The natural realities (the bread and wine) wholly disappear.

My proposed understanding of transubstantiation is closer to the Lutheran conception-that the body and blood of Christ are presented “in, with, and under” the forms of bread and wine-and so presents the possibility of fruitful ecumenical dialogue. Yet it is still possible to say, as the Catechism states, that “there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord,” because the bread, while not ceasing to be (chemically) bread has come to inhere, exist, and be held in being within another substance, the risen and glorified body of the Lord.