The Doctrine Of The Eucharist and Aristotelian Metaphysics
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The Doctrine Of The Eucharist and Aristotelian Metaphysics

The Doctrine Of The Eucharist and Aristotelian Metaphysics

Dr William Newton FAITH MAGAZINE January - February 2015

At first sight, the doctrine of the Eucharist and Aristotelian metaphysics seem worlds apart. The doctrine of the Eucharist is among the most sublime of the mysteries of faith whereas metaphysics holds the foundational place in the realm of pure reason. Yet, in St Thomas Aquinas’s exploration of the doctrine of the Eucharist, the two worlds come together with such exquisite harmony that it appears as if they were made for each other.

In this essay, I wish to briefly survey this harmonious relationship as perhaps the supreme example of reason at the service of revelation, or of philosophy as the handmaid to theology. Such a survey will also demonstrate the need for at least a basic grounding in philosophy, if we are to better understand and communicate the mysteries of our faith.

What You See is Not What You Get

At the heart of the doctrine of the Eucharist is the assertion that while the appearance before us is one of bread (or wine), the substance present after the conversion is Christ’s Body (or His Blood). As Aquinas puts it in his hymn “Lauda Sion”:

Sub divérsis speciébus,

Signis tantum, et non rebus,

Latent res exímiæ.

[Here beneath these signs are hidden,

Priceless things, to sense forbidden,

Signs, not things, are all we see.]

On the one hand, we assent to the presence of the substance of Christ’s Body because we accept the truth of Christ’s own words that “this is My Body” (Lk 22:19). On the other hand, we assent to the continued presence of the accidents of bread from the fact that we trust our senses.

That something can be different in appearance from what it is essentially can easily be catered for within Aquinas’s Aristotelian philosophical system because one of the most basic distinctions is between substance and accident. Substance points to what a thing is, whereas accident points to some lesser characteristic of the thing. That these two realities are distinct can be seen from the fact that Peter can change shape (pudge out), colour (get a sun tan), gain new relationships (become a father), acquire a new habit (learn Latin), and so on without changing what he is: he remains a human being throughout. If substance is distinct from accident (and so accidents can change without the substance changing) then, while it is amazing that what appears to be bread is actually the Body of Christ, this is not a contradiction, because in this case, the substance has changed without the accidents changing.

A Unique Conversion

Dogma datur christianis,

Quod in carnem transit panis,

Et vinum in sanguinem.

[Hear, what holy Church maintaineth,

That the bread its substance changeth,

Into Flesh, the wine to Blood.]

The conversion of the bread into the Body of Christ (and the wine into the Blood of Christ) must be a conversion of a unique kind. It cannot be categorised as a normal type of substantial change, what is called a transformation. When something is transformed – when, for example, grass is eaten and digested by a sheep – one substance is converted into another substance, since the grass is taken up (at least in part) into the body of the sheep. In such cases, the accidents of grass (such as its colour and texture) pass away with the change in substance. This is, quite evidently, not the case in the conversion of the bread into the Body of Christ: the accidents of bread remain; we clearly see them before us.

Moreover, in a transformation the matter of the thing being converted passes over into the terminus of the conversion. When the sheep eats the grass, the matter of the grass passes over into the sheep. This cannot be true in the case of the Eucharist because, if it were, then each confection of the Eucharist would add to the matter of Christ’s body! Yet, Christ has his own discreet quantity of bodily matter. So, on account of the accidents remaining and on account that this conversion does not add to the matter of Christ’s body, this conversion simply cannot be a transformation.

The Church has given this conversion the name transubstantiation.1 To see why this word is apt, we need to delve a little more deeply into the difference between transubstantiation and transformation. The idea of transformation rests upon what is called the hylomorphic theory, another stalwart principle of Aristotelian philosophy. This is the idea that all material things are the composite of a material and formal principle. The formal principle (the form) configures the matter to be a certain type of matter: a human body if the form is human, an oak tree if the form is that of an oak tree, and so on.

In a transformation, when substance A (eg grass) becomes substance B (eg sheep flesh), the matter of substance A endures throughout the conversion and continues on as the matter of substance B, yet the form of substance A becomes the form of B. The matter remains but there is a change in form, hence the word transformation. In transubstantiation, however, the whole substance (the form-matter composite) of substance A (bread) is converted into substance B (the Body of Christ): hence the word transubstantiation. Precisely how this happens we cannot say, but it is certainly within the power of God to do this. Every created agent is limited to bringing about a change in form only (a sheep can transform grass into its own body matter by digestion), but God – as the ultimate cause of all being – can surely bring about changes at the level of being: converting one entire substance into another.

To explain this unique conversion further, some theologians have proposed the theory of adduction. This says that the conversion is a two-step process: first, the annihilation of the substance of the bread; second, the coming to be of the Body of Christ where the bread once was. Aquinas opposes this on two grounds. First, if the Body of Christ does not come out of the bread, then the Body must move from where it was prior to the consecration to where the bread was occupying space: but we do not see that happening. Second, the sense of Christ’s own words, “this is my Body,” implies that what was bread is now His Body. If there were no real connection between the bread and the Body, Christ ought to have said “that is my Body.” The pronoun “this” implies a connection between the bread and the Body, such that the substance of Christ’s Body comes out of the bread.2 Finally, there is a powerful argument of fittingness. If the bread is just replaced, it is not clear how what is offered in the Mass is really our offering. Only when what we offer – bread and wine – is connected with what the priest offers to the Father after the consecration, namely the Body and Blood of Christ, can we truly say that this is our offering to God.3

Self-Subsisting Accidents

As I have already intimated, the doctrine of the Real Presence relies upon us believing Christ when he says “this is My Body” and believing our senses when we see before us the appearance of bread. From these two points of reference, we must conclude that the accidents of bread (that clearly do remain after the consecration) are self-subsisting, which is to say that they do not exist, as accidents normally do, in a substance. They cannot exist in the substance of bread since the bread is no longer present and they cannot have their existence in the substance of Christ’s body because the substance of a human body is not the proper substance for the accidents of bread: human bodies simply do not have the texture, colour, and so on, of bread. By deduction, then, the accidents of bread must exist independently of any substance.

At first sight, this would seem to be a contradiction even from within Aristotle’s own philosophical system. The very definition of a substance is that which exists in itself and not in another thing, whereas accidents are defined precisely in contra-distinction to this: they exist in something else, namely in a substance.

The way out of this seeming contradiction is to mount another distinction within Aristotle’s philosophical system, this time the distinction between primary and secondary causality. For Aristotle and Aquinas, the universe is full of secondary causes. These are beings that have quasi-autonomous causal power. For example, apple trees have inherent power to produce apples: apple trees are the secondary cause of apples. However, I was careful to say quasi-autonomous because, among other things, given that secondary causes (like apple trees) do not account for their own existence, they must receive both their existence and their causal power from a primary agent (aka God). Hence, if the primary cause wants to bypass or leap-frog the secondary cause and produce the effect directly … he certainly may.

“Every created agent is limited to bringing about a change in form only, but God can bring about changes at the level of being”

The point here is that substances are the secondary cause of the existence of accidents. Substances really have the power to give existence to their accidents (eg the substance of bread really does cause the existence of the colour and texture of bread). However, this causal power is ultimately from the primary agent. Hence, if God wants to hold the accidents of bread in existence without the proximate causal activity of the substance of bread … he certainly may.

The Totality of Presence

The doctrine of the real presence includes the assertion that Christ is fully present under both species (under the appearance of bread and under the appearance of wine) as well as fully present under each particle of each species. The latter means that when a consecrated host is fractured into two, Christ is fully present in each half.

Of the first totality, the poet Aquinas writes:

Caro cibus, sanguis potus:

Manet tamen Christus totus,

Sub utráque spécie.

[Flesh from bread, and Blood from wine,

Yet is Christ in either sign,

All entire, confessed to be.]

Of the second, he says:

Fracto demum Sacraménto,

Ne vacílles, sed memento,

Tantum esse sub fragménto,

Quantum toto tégitur.

[Nor a single doubt retain,

When they break the Host in twain,

But that in each part remains,

What was in the whole before.]

The explanation of how Christ is fully present under each species requires us to consider how Christ is made present in the first place. An important principle of sacramental theology is that Sacraments cause by signifying. They are not just signs and causes of grace but, rather, signs that cause grace. Now, we should note that the priest confects the Eucharist by saying over the bread, “This is My Body,” and over the wine, “This is My Blood.” From the words alone, only the Body of Christ is made present out of the bread and only the Blood of Christ is made present out of the wine.

If this were all there was to it, Christ would not be wholly present under each species: under the bread there would be only his Body and not his Blood, or his Soul or His Divinity. So we need to add that something can be made present not only on account of the force of the words uttered by the priest but on account of what is called natural concomitance.4 This means that whatever is actually connected with the Body of Christ (or the Blood of Christ) is made present when the Body (or the Blood) is made present.

Now, Christ is made present in the Eucharist as He really is – it is not another Christ that is made present. Hence, since (after the Resurrection) the Body of Christ is united to his Blood and his Soul and all these, in turn, are hypostatically united to the Word of God, when the Body is made present so also are the Blood, Soul, and Divinity. Likewise, when – by the force of the words spoken by the priest – the Blood is made present under the continued appearance of wine, the Body, Soul and Divinity of Christ are made present by natural concomitance.

This, then, explains the total presence under each species: what about the total presence under each part of each species? Here we must go back to what we said about transubstantiation. We saw that this was a unique type of conversion because, while the substance changes, the accidents of bread remain. And, since the accidents of the bread remain, this means that the accidents of Christ’s own body are not expressed. They are present (because Christ’s body is present) but they are quite evidently not expressed. I say “quite evidently” because if the accidents of Christ’s body were expressed, we would obverse startling changes in a consecrated host: for one thing it would grow to the size of a man (the man Jesus) and take on the shape of a man: since quantity and shape are accidents.

That quantity with its associated dimensions is an accident is clear from the fact that I can change my quantity and dimensions without becoming other than what I am – a human being. Quantity under given dimensions is also what extends a thing in space so as to make one part of that thing separate from the other parts. It is because I, the author, am extended in space that one part of me, let’s say my right arm, could be got hold of separately from the rest of my body and broken off from the whole. But since in the Eucharist, the accident of quantity proper to Christ’s body is not expressed, the parts of Christ’s body are not spread out into different parts of space; hence breaking off a piece of the host does not entail breaking off one part of Christ’s body from another part.5

Beyond Physical Presence

The fact that the quantity and dimensions of Christ’s body are not expressed also explains how Christ’s presence in the Eucharist surpasses the limitations of physical presence, this limitation being that a body can only be in one place at one time. Obviously, Christ’s Eucharistic presence is not limited in this way because He is truly and substantially present in every consecrated host in every tabernacle of the world.

It is on account of the quantity of a material substance (like a human body) under certain dimensions that it is located in a place. It is because a body fills up a certain amount of space that it is located in that place and, thereby, not in another place. But when a thing is not present with its quantity or dimensions, it is not limited in this way. Another way of saying this is that Christ’s Body is not located by its Eucharistic presence and so not fixed to a single location.6


It is important to be clear as to what we have been up to here. We have not mounted philosophical arguments that prove Christ is really present in the Eucharist despite appearances, or that He is wholly present in each part of each consecrated host; nor have we proved, from reason alone, that He is really present in a consecrated host in the Cathedral of Tokyo and Paris at the same time. These things we assent to by the virtue of faith. However, what we have done, with the help of Aristotle, is show how these amazing assertions are not contradictions – they are not impossibilities.

I like to picture Virgil returning to his own circle in hell (which is actually more like limbo and which he shares with Aristotle) after finishing his tour of the after-life with Dante. During his visit to the fourth sphere of paradise, he bumps into a certain resident there, Thomas from Aquino. Thomas gives to Virgil a copy of his poetic hymns Lauda Sion and Pange Lingua. He also gives something to Virgil to pass on to Aristotle: a copy of the eleven questions on the Eucharist from his Summa Theologiae. Just imagine the astonishment and great satisfaction that Aristotle might experience in seeing how dextrously his philosophy expounds and defends the truth of the doctrine of the Eucharist. Turning to the inside cover of the book he sees inscribed in free-hand the dedication: “To the Philosopher with thanks: I couldn’t have done it without you!” Anyhow, that’s how I like to think of it.  

Dr. William Newton is the associate professor of theology at Franciscan University of Steubenville and is based in Gaming, Austria.


1Decree of the Council of Trent on the Eucharist, Canon 2, Denzinger 884.

2St. Thomas Aquinas, Summa Theologiae, III 75.2.

3Cf. Matthias Scheeben, The Mysteries of Christianity (London: B. Herder Book Co, 1946), 500-501.

4Decree of the Council of Trent on the Eucharist, Denzinger 876.

5St. Thomas Aquinas, Summa Theologiae, III 76.3.

6St. Thomas Aquinas, Summa Theologiae, III 76.5.

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