Recovering the Substance of Eucharistic Doctrine: Logic, Metaphysics, and the Conceptual Framework of “Transubstantiation”


by Dr. Joshua Hochschild
Professor, Mount St. Mary’s University
St. Vincent de Paul Lecture & Concert Series,
March 7, 2024
Lecture Handout (PDF)


0. Preface

At the outset I want to acknowledge a sense of unworthiness and even ridiculousness. I am going to talk about the Bread of Life, about Christ in the Eucharist, and how this was understood by a great theologian, your patron Saint Thomas. More than that, I am going to talk as a philosopher about a theologian who was also a poet. Sertillanges said that “St. Thomas is, properly speaking, a metaphysical poet, taking the word in its broadest sense to signify one who interprets the universe: a prophet of being—of God, humanity, nature” (A. G. Sertillanges, O.P., Foundations of Thomistic Philosophy, trans. Godfrey Anstruther, 1931, p. 9). And Thomas is undoubtedly the Church’s greatest poet about the Eucharist. The great literary critic Hugh Kenner, reflecting on the Pange Lingua as a consummation of Western linguistic genius, described Thomas’s poetic virtuosity as taking words the very limits of their capability, attempting “a virtual transubstantiation of language” (Hugh Kenner, “Rhyme: An Unfinished Monograph,” in Common Knowledge 10 [2004]: 377-425). I acknowledge this only to distance myself from any such attempt, and to clarify that at best I can hope to speak with the plain and sometimes plodding clarity of a philosopher, without the literary virtuosity of a holy poet.

I. Introduction

In the Eucharistic sacrifice of the Mass, “the source and summit of Catholic life” (Catechism of the Catholic Church ¶1324; cf. Lumen Gentium ¶11 and Mediator Dei ¶5), it becomes true to say of the consecrated host that it “is the body of Christ.” From the perspective of Catholic faith, that this becomes true is not up for debate, but how it becomes true, how to interpret its truth, the sense in which the host is the body of Christ, and what exactly is going on in the realities signified by the words such that that claim comes to be true, have been historically rich, often puzzling, and sometimes very contentious questions. So while, for Catholics, there is no theological dispute about whether the consecrated host is the body of Christ, the questions about how that is true invite theologians who want to articulate and expound this truth to enter into rational inquiry, engaging with logical and metaphysical concepts, distinctions, and arguments, and more generally depending on the foundational dialectical resources of the liberal arts.

At a certain point in the history of the Church, it became common to account for the Eucharistic miracle partly in terms of two key words: substance, and conversion. The consecration of the bread involves a kind of change of something into something else (conversion) such that a substance that was not there before (Christ’s body) comes to be where another substance (the bread) had been, and indeed that the substance of the bread is no longer there because that is precisely what was converted into the substance of Christ’s body. This account of the change—the substance of bread being converted into the substance of Christ’s body—is what is captured by a single well-known theological word, transubstantiation.

For a variety of historical reasons, Saint Thomas Aquinas’s articulation of the doctrine of transubstantiation came at a propitious time. In the middle of the 11th Century, Berengar of Tours was made to repudiate a view denying that the substance of bread changes in the Eucharist, and the Church started to insist more strongly on “substance” as the most apt word to describe the actuality of Christ’s body in the Eucharist. In the early 13th Century (1215, ten years before the birth of Saint Thomas) transubstantiation was dogmatically proclaimed at the Fourth Lateran Council under Pope Innocent III.

By the time Aquinas was writing a few decades later, many new Aristotelian texts were being discovered for the first time in the Latin West. Substance was not, in itself, a technical philosophical term, but no philosopher had explored and expounded on the notion of substance and the principles of change more thoroughly than Aristotle. Aquinas thus found it natural and useful to employ, with great refinement and care, Aristotelian concepts, distinctions and arguments to articulate the Church’s teaching on transubstantiation.

Later challenged by Protestant reformers, transubstantiation—and implicitly Aquinas’s defense of it—was reaffirmed in the Council of Trent (in 1551), and it has been reaffirmed consistently since then, including in Paul VI’s 1965 encyclical Mysterium Fidei and in the modern Catechism of the Catholic Church (¶1376 and ¶1413). The doctrine of transubstantiation is thus often taken as a distinctive mark of Roman Catholic faith, and in Christian discourse outside of Roman Catholic faith (as well as frequently within it), it has become common to ask whether there are alternative ways of affirming Christ’s real presence in the Eucharist, without the specifics of transubstantiation or the apparent “baggage” of Aristotelian concepts.

In this talk, I want to explore why, from the perspective of Aquinas’s conceptual framework, the doctrine of transubstantiation was not at all controversial, and the use of Aristotelian concepts was not regarded as importing some kind of speculative philosophical theory and imposing it on the mystery of the Eucharistic miracle. For Aquinas, to speak of the conversion of substance, and to articulate that in Aristotelian terms, was a common-sense and coherent way to accurately identify and articulate what the Church, and Jesus himself as reported in Scripture, had always taught about that miracle and its mysteriousness.

However, the lucidity that Aquinas saw in the doctrine of transubstantiation is often obscured from our perspective, because of two related systemic obstacles to understanding Aquinas’s conceptual framework. These obstacles are all the more frustrating and difficult to overcome because they are in matters of first principles – of metaphysics, and of logic: on the one hand, a loss of a once common conception of substance; and on the other, a loss of a once common account of how words signify.

This situation means that recovering these lost notions – of substance, and of the way words signify – is necessary for us even to understand Aquinas’s position on transubstantiation – not so much to agree with it, but to be able to comprehend it enough so make possible an act of agreeing or disagreeing. Sketching a path toward this recovery, suggesting its possibility and its utility, will be the heart of the lecture.

I mean this lecture to be an exercise in reading and thinking about Aquinas’s treatment of the Eucharist in the Summa Theologiae, which I understand is assigned for all seniors at the college. I will also draw at least indirectly from other texts that are part of the curriculum, including especially Aristotle’s Categories, Physics, and On Generation and Corruption, and from Aquinas’s On the Principles of Nature and On Being and Essence.

These are all dense and difficult texts, but my overall goal of advocating and enacting conceptual recovery is modest here: it is not to persuade you that the doctrine of transubstantiation is true, but to make it possible to apprehend that Aquinas had a coherent account of language and causality such that the doctrine of transubstantiation would naturally express what he took to be a central truth of Christian faith.

The benefits of such recovery should be obvious. I do think it can have personal, spiritual significance, insofar as it can help the faithful Catholic enter into the worship of the Mass, with better understanding the miracle of Christ’s Eucharistic presence. I also believe this recovery work has pastoral and ecumenical significance, insofar as it can help Christians in and outside of the Catholic fold better to understand where they do and don’t disagree about the Eucharist and negotiate those disagreements more carefully. Most immediately, and perhaps most fittingly for a celebration of Aquinas in an academic environment that attends closely to reading texts and practicing arguments, I believe that gestures of conceptual recovery offer a unique test and exhibition of the value of liberal education and the crucial dialectical activity, in pursuit of truth, especially truth about first principles, that must be at its heart.

II. The Text of the Summa Theologiae: Challenging Common Assumptions

As is often the case when turning to Aquinas’s Summa Theologiae, the challenge is not so much that we don’t share Aquinas’s theories, or that we don’t accept the answers that he gives to questions. Rather it is that we don’t share his dialectical perspective: we aren’t asking his questions.

This is conspicuous because of course questions are the building blocks of the Summa. The Summa is meant to embody, refine and preserve a practice captured in medieval disputation but which goes back through Aristotle’s aporetic method and Plato’s literary dialogues to the viva voce dialectic of embodied Socratic inquiry. The Summa is structured with and around questions, and not simply a list of questions but hierarchies of embedded questions. The most common architectural metaphor for the Summa is that it is cathedral, which naturally evokes grandeur and nobility, but should also call to mind careful attention to detail and order, symmetry and variation, across larger and smaller scales. The Summa’s design is fractal, interrelating and embedding questions across telescoping layers covering different scopes of inquiry.

So the treatment of the Eucharist—one may call it a “treatise” on the Eucharist—appears within a section of the Summa on the sacraments in general, which appears after a section on Christ. All of that appears in the third of three main parts of the Summa, on salvation, which appears after the first part inquiring into God and creation, and the second part inquiring into human life (the long, central “moral” part).

Turning to the treatment of the Eucharist, the first thing that might strike even a theologically well-informed modern reader is how long it is: it takes up questions 73 through 83 of the Third Part. There are a total of 84 dialectical queries, or “articles,” organized under the heading of 11 general areas of investigation, or “questions.” (One could add more, for instance Q. 65, A. 3, “Whether the Eucharist is the greatest sacrament.”)

So I think the second thing that would strike a reader of this section on the Eucharist is the oddity of some of the questions raised. Here is a sample of what Aquinas asks:

Whether the sacrament is suitably called by various names? (73.4)

How much water should be added to the wine? (74.8)

Whether Christ’s body is movably in the sacrament? (76.6)

In what sense do the accidents of the bread and wine have causal power? (77.3-6)

In what sense are the words of the consecration appropriate? (78.2-3)

There are eight articles about how the Eucharist bestows grace (79), and twelve articles about the suitable reception of the Eucharist (80). When formulating questions about the institution of the Eucharist at the Last Supper, Aquinas asks whether Christ himself received, and whether Judas received (81.1 & 2). There are ten articles about the minister of the sacrament (e.g. article 6: “Is the Mass of a wicked priest of less value than that of a good one?”) and there are six articles about the rite, or circumstances of celebrating, the Eucharist.

And of course, given what I’ve called the Summa’s “fractal” character, in addition to the 84 queries of the articles, of course within the parts of articles – in the objections, body, and replies – there are very often further even more specific questions raised and answered, to clarify distinctions, illustrate concepts, defend premises, or entertain and counter misinterpretations. Are bread and wine substances? Why are the words of consecration in the present tense? What are the most proper names to call the Eucharist? (In his commentary, Cajetan includes a long discussion of why pasta cannot serve the same role as bread!)

In short, on first inspection the treatise on the Eucharist seems to give rise to a large quantity and diverse quality of questions, exactly the experience that gives legs to the old joke that a Thomist is someone who has answers to what you didn’t even know were questions. And yet in all seriousness the challenge of reading Aquinas is learning to appreciate and in some sense share the questions that he asks, to understand why they arise and what is at stake in answering them. Obviously one doesn’t do that simply by seeing what answers he gives to the questions. The Summa is not a theological dictionary recording information to be looked up. The Summa is a record and model of active thinking, and we read it by learning to share its questions; its design is meant to “inform” not in the sense of delivering content to passive minds, but in the sense of inviting the reader into new habits of thinking, reshaping how the reader’s mind actively seeks understanding.

In the case of the Eucharist, even if, for our purposes—trying to understand Aquinas on transubstantiation—we exclude more practical or pastoral kinds of questions about the observance, use and benefit of the sacrament, and focus on the more metaphysical questions about what it is, we are left with 16 articles, eight each under two questions: Question 75, on the conversion, the change of the bread and wine into the body and blood of Christ (and so sometimes said to be about “transubstantiation”), and Question 76, on how Christ has being, or the mode by which Christ exists, in the Eucharist.

Question 76 is sometimes said to be about “the real presence”—it is common for that phrase to appear in English translations or descriptions. But this leads me to observe a second source of potential frustration. I believe that even narrowing our focus to Questions 75 and 76, a typical modern reader could be frustrated, for something else that is often surprising when we turn to Aquinas is what seems to be missing, the questions he does not ask. Anyone passingly familiar with historical or systematic theology today, relying on trustworthy accounts of Eucharistic doctrine, might turn to Aquinas asking, and expecting him to address, such questions as:

  • Is it appropriate to use Aristotelian philosophical categories to interpret the Eucharist?
  • Is transubstantiation the only way to articulate the orthodox understanding of the reality of Christ in the Eucharist?
  • Do we even need to have a metaphysical account of the Eucharist?

Not only are questions like these not formulated or addressed, but one does not even find Aquinas asking the obvious question, the question that one might think is central to any responsible Catholic teaching about the Eucharist, presumably a necessary preliminary to any discussion of transubstantiation: Is Christ really present in the Eucharist?

To summarize, then, on first approach a modern reader seeking to understand Aquinas’s metaphysical account of the Eucharist is likely to notice, when turning to the text of the Summa:

  • That there are a large number of articles or inquiries,
  • Including about problems that might not seem to arise today, or might not seem important to us;
  • But Aquinas does not ask about the fittingness of using Aristotelian conceptual categories,
  • And strictly speaking he does not formulate any inquiry about “real presence.”

Noticing this, we have to realize that we come to the text asking different questions than the author. This could mean that to understand Aquinas we need to translate our questions into the questions he was asking; but it could also mean that we need to set our questions aside and try to understand the questions he is asking, and let his questions challenge our questions, sometimes perhaps reformulating them or at least helping us to see what assumptions we were making in asking them.

III. What Does Aquinas Say about “Real Presence”?

I mentioned that Aquinas does not formulate a question about “the real presence.” In fact he doesn’t talk about “real presence” at all! The expression “real presence” does not occur in the Summa, or elsewhere in Aquinas as far as I know.

To be sure, Aquinas is willing to talk about the metaphysical status of the Eucharist, and we may want to loosely translate what he does say as concerning “real presence,” but even if we want to make this translation we should notice that his own terminology is tellingly different.

Where English translations sometimes talk about Christ’s “presence in the Eucharist,” the Latin typically has simply Christ’s being in the Eucharist. So we find Aquinas asserting the being of the true body and blood of Christ in this sacrament (verum corpus Christi et sanguinem esse in hoc sacramento). He will commonly say that the Eucharist really contains Christ (realiter continet Christum) or that it contains Christ Himself (continet ipsum Christum). So instead of what we might expect him to say, about Christ being “really present” in the sacrament, Aquinas has it that the body of Christ, or Christ himself, truly is in, or is really contained in, or has being in the sacrament.

In question 75 (about the Eucharistic conversion) Aquinas will sometimes talk about Christ’s bodily presence, but in question 76 (the one often characterized as about “real presence”) even that phrase, “bodily presence,” does not occur. Question 76 is about the mode of Christ’s being in the Eucharist. But the individual articles make clear that Aquinas is assuming and not defending that Christ has a substantial mode of existence, and is exploring what follows from that. So the articles ask: Whether the whole of Christ is in the sacrament (1), under each species (2), and in each part of each species (3), whether the dimensions of Christ’s body are in the sacrament (4), whether Christ’s body has location in the sacrament (5), whether Christ’s body is moved by the sacrament being moved (6), whether Christ’s body is visible (7), and whether it remains even when the Eucharist appears as something other than bread and wine (8)? In answering these, Aquinas has occasion to expand on what it means that Christ’s body is substantially in the Eucharist, but each of the questions presumes that mode of being and arises from it.

IV. Instead of “Real Presence”: Kinds and Causes of Truth

To get anything like a defense of the fact that Christ’s body is substantially in the Eucharist, we have to look earlier. There is an early indication that the substantial mode is important: a key passage before the “treatise on the Eucharist,” in a discussion of the sacraments in general, characterizes the Eucharist as the greatest among the sacraments because it is the only one “containing Christ substantially” (65.3.c) and so it is even that in which “the common spiritual good of the whole Church [namely Christ] is contained substantially” (ad 1).

We don’t find an actual argument for Christ’s substantial being in the Eucharist except at the beginning of Question 75. It is based on the words of consecration, taken from Scripture, Jesus’ own words from the institution of the Eucharist at the Last Supper: This is my body. So Article 1 does not ask what we might want it to ask: “Is Christ really present in the Eucharist”. It rather asks: “Is Christ’s body truly in the Eucharist, or only figuratively?” The fact that this article is not on the first among those considering metaphysical issues, but is new to a list of queries that otherwise had earlier appeared in Aquinas’s treatment of the Eucharist in the Sentences Commentary, suggests that it deserves special attention. (It is also worth noting that a similar formulation is in Aquinas’s Commentary on the Gospel of John: “The truth of this sacrament is indicated when he says it is my flesh. For he does not say, it signifies my flesh, but it is my flesh, for in reality that which is taken is truly the body of Christ” (Ch. 6, 962; Veritas autem huius sacramenti insinuatur cum dicit caro mea est. Non dicit autem carnem meam significat sed caro mea est; quia secundum rei veritatem hoc quod sumitur, vere est corpus Christi).

So is Christ in the Eucharist truly, or only figuratively? We might say more loosely: Is the assertion that Christ is in the Eucharist literally true or is it only a figure of speech? For Aquinas this is an exhaustive distinction: All assertions are about what is, and this can be either what is according to truth (so that what is asserted as being, really is) or what is figuratively (so that what is asserted as being, isn’t really but may still be helpful or meaningful to suggest). “The warrior is courageous,” is an assertion according to truth; “The warrior is a lion,” is a figurative assertion, poetically comparing the warrior to a lion but not truly claiming that he is one.

On its own, this according to truth vs. according to figure distinction might not seem to do as much work as it obviously does here for Aquinas. For one could think that it is true and proper, and not a mere metaphor or poetic figure, to say that the Eucharist is the body of Christ, but still analyze the truth in such a way that avoids attributing Christ’s actual body, or any intrinsic reality at all, to the Eucharist. One could have a view, for instance, according to which it becoming true that the Eucharist is Christ’s body is just a matter of a ritual being performed, in a certain context, so that those who participate in the ritual are authorized to now think of the bread and wine in some new relation to “the body of Christ,” where that truth is based on something extrinsic to the bread and wine (which in themselves remain what they are as bread and wine).

This might sound like a denial of real presence, but historically some accounts of the Eucharist as a kind of “symbol” were not presented as rejections of real presence so much as alternative accounts of real presence unencumbered by the contested, outdated scholastic notion of “substance.” This is the charitable read of some versions of “transsignification,” “transfinalization,” and other interpretations of Eucharistic “presence” by anti- or post-metaphysical theologians. Such approaches may seem confused or disingenuous, and in some cases they may indeed be so, but in principle it is not necessarily incoherent to insist that in some cases at least the truth, and thus the “reality,” of something, or even its “presence,” can come to be from only an extrinsic or relational change in the circumstances in which it is considered, not some change in the thing itself.

Let me make use of a mundane example. Suppose my chess set is incomplete and in order to play a game of chess I use a salt-shaker as one of the pawns – in a sense “consecrating” the salt-shaker as a pawn. If you see me playing chess with a salt-shaker on the board and ask me if the salt shaker really and truly is a pawn, in the context of the game I can honestly say, “Yes of course it is!” It is certainly not metaphorically or figuratively a pawn (in the way that, say, you may be called a “pawn” if you are being used by someone as part of their political schemes). And this saltshaker pawn is surely present to me as a pawn; I could even talk about the formal “pawn-ness” of the pawn (what makes it to be a pawn, which is after all simply it being subordinated to conventions about its use, a set of relations that the physical item has to the board, the other pieces, and the rules for manipulating the pieces on the board in the context of the game). If I’m playing chess and using the salt-shaker as a pawn, it being a pawn, and even the pawnness by which it is a pawn, are really present to me.

If at this point you wanted to quibble and say that the salt shaker is not really a pawn, that it only represents or signifies or symbolizes or stands in for a “real” pawn, I would of course know what you mean, but then we would not really be arguing in any meaningful way, we would only be talking past each other, and your alternative account of the salt-shaker “pawn,” whatever your motivation – perhaps because you want to sell me a “real” pawn, which after all is just some physical object that was always intended to play the role of pawn rather than something that was conscripted into playing that role – would be rather irrelevant to whether you were capable of comprehending my use of the salt-shaker as pawn, which even from your perspective is not “figurative” or “metaphorical.”

So to review this example: it seems like we can take something (a salt-shaker) and give it a new name (“pawn”), such that we can say truly, and not merely metaphorically or figuratively, of that something that it is a pawn, and we can say that the truth of this assertion is even on account of some reality or mode of being – namely, the relation it has to other pieces and rules in the context of a game – where there is no doubt that that reality or mode of being has absolutely nothing to do with some intrinsic change in our original object: in this case, it is extrinsic, relational, and a matter of social convention. While it really is a pawn (because of extrinsic factors) it is also in itself still really a salt-shaker and hasn’t undergone any intrinsic change. 

Clearly then Aquinas thinks that when a priest in the context of a Mass says “this is my body” of the Eucharist, something very different is going on than when I, in the context of a chess game, say “this is a pawn” of a salt-shaker, for Aquinas’s view is that what was bread no longer is bread and has been converted into the body of Christ, and the being of the Eucharist as Christ is not merely some extrinsic factor, relation, or product of social convention, but a conversion of one substance into another (obviously depending on some supernatural power).

Moreover, since Aquinas would certainly be able to follow my example of a non-pawn truly and not figuratively “consecrated as” a pawn, Aquinas must think that when we distinguish between true and figurative predications, that distinction alone is not enough to draw some thick metaphysical inferences about what the two kinds of predications reflect. So what else is going on such that Aquinas believes that a true predication in this case implies a real change?

While Aquinas does not defend and elaborate on it in the treatise on the Eucharist, clearly he is assuming that his audience is familiar with a then-common distinction between different kinds of true predications: substantial and accidental. Notice from the way that we were describing the shalt-shaker as a chess piece we were clearly characterizing the being of the chess piece as what Aristotle would consider an accidental mode of being, that is, something that in coming to be does not change the underlying reality in which it exists. Whether it is a typical pawn in a chess game (a piece of wood carved into a characteristic shape), or an ad hoc emergency pawn (such as a salt-shaker), what makes it a pawn doesn’t change what it was before it was a pawn (wood or salt-shaker).

Aquinas’s argument about the truth of the predication in This is the body of Christ obviously depends on the predication being not only true (as opposed to figurative) but also substantial (as opposed to accidental). Aquinas does not think being the body of Christ is an accidental reality, and this is not simply because there is an authoritative dogma about the Eucharist containing Christ’s “substance.” There are perfectly natural reasons to hold that the coming to be of a person’s body is a substantial change, and not an accidental one. “Body” is a genus term in the category of substance – a human being is a certain kind of body, namely a living, sensitive, rational living body. Bread is also substance, something whose unity is not only accidental or the result of artifice. Aquinas even takes time to defend that bread is a substance, in Q. 75, a. 6, objection 1 and reply, since it could seem that bread is an artificial thing, as the work of human hands. Merely mixing ingredients might create an accidental, artificial unity, but bread is also the product of the activity of nature: the chemical reactions of the mixed ingredients, and heat in process of baking, generate bread from the dough: there is a new nature in the bread, which after all is made from, but not made of, flour and water.


V. Reconstructing Aquinas’s Argument for Christ’s Being in the Eucharist

So to make sense of Aquinas’s argument in 75.1, we need to rely on the distinction between substantial and accidental predications. If there were any doubt that Aquinas would think in these logico-grammatical terms in the context of the Eucharist, he explicitly affirms in 75.8 that the words of consecration employ a “substantive verb in the present tense.” So to analyze the truth of the statement This is the body of Christ, one has to grasp the nature of the predicate, and realize that signifying Christ’s bodiliness is signifying a substantial reality and not an accidental one, so that to affirm of something that it is the body of Christ is to make a claim about its substantial nature.

So now we can make explicit the assumptions Aquinas is making in Question 75, Article 1, and spell out the logic of his reasoning including implicit premises that would have been easily understood by his contemporary audience:

  1. Upon consecration it becomes true to say of the Eucharist, “This is the body of Christ”.
  2. In that statement, “is the body of Christ” is a substantial predicate.
  3. A true substantial predication signifies the actuality of the substantial form signified by the predicate in the subject.
    It follows that:
  4. Upon consecration, the substantial form signified by “is the body of Christ” comes to be actual in the Eucharist.
  5. For a substantial form to come to be actual is for the substance of which it is the form to come to be.
    And of course:
  6. The substantial form signified by “is the body of Christ” is Christ’s bodiliness.
    So it follows (from 4, 5 & 6) that:
  7. Upon consecration, the Eucharist comes to be the substance of Christ’s body.
    Further (and to extend this reasoning to the real subject of Question 76, which is not about the fact of “real presence” but about the implications of substantial presence):
  8. The substantial form that is Christ’s bodiliness is the one whole substantial form of Christ, only named in respect of its material degree of actuality.
  9. In that one substantial form, other degrees of actuality of Christ (such as His life, divinity, etc.) accompany the material degree of actuality (in Aquinas’s phrase, “by concomitance”).
    It therefore follows (from 5, 8 & 9) that:
  10. Upon consecration, the Eucharist comes to be the substance of Christ.

Now this has been a lot of work to make sense of one article about the Eucharist that seems relevant to, though it differs from, an article about “real presence,” namely, the article defending the substantial bodily being of Christ in the Eucharist. And by filling in details, and making explicit elided steps in the reasoning, I may not have made it more convincing, as I have added further questionable concepts and assumptions that would themselves need further elucidation and defense. My goal has been to help you see the “logic” of Aquinas’s reasoning, in the sense of the kinds of necessary inferences, but also to help you better understand that there are very basic assumptions in the implicit “logic” of the mind that would naturally think in terms of the propositions that make such inferences possible. So I offer this argument, not to try to convince of its conclusion, but to begin to make intelligible a new way of conceiving of the question of Christ’s “presence” in the Eucharist.

VI. Substance and Signification

What I especially want to highlight is that Aquinas’s reflections on the Eucharist presume, and make no sense without, a notion of substance, and a notion of how words signify in true propositions. Some reflections on each in turn.

About substance: As this notion appears in Aquinas, it is sometimes articulated with the help of Aristotle, but as in Aristotle it is taken to be an already available, pre-philosophical concept that is part of the way human beings naturally make sense of the world in the normal course of life. Understood as Aristotle and Aquinas do, the distinction between substance and accident is not an optional conceptual dichotomy that one can choose whether to adopt or not, rather it is the most basic distinction that we find in the world and the only area of contention is in particular judgments about which things count as substances. Even such different philosophical views as Democritean atomism, Pythagoreanism, or Parmenidean monism, don’t avoid the distinction between substantial and accidental modes of being, they merely posit different kinds of things as the most fundamental substances: particles, numbers, or the whole of what is.

For two reasons, it is even misleading to consider substance vs. accident as a strictly “metaphysical” distinction. First, while it is heavily scrutinized in Aristotle’s Metaphysics, it emerges in Aristotle’s reflections on change, and the different modes of “coming to be” in his works on natural philosophy. And second, it is reflected in the operations of our minds and the interpretation of our speech as much as in the natures of things, which is why it appears also at the opening of Aristotle’s logical works: the distinction between substance and accident is the difference between what is not in and what is in a subject, as described the beginning of the Categories.

This brings us to the second issue, about truth and the signification of words. What I have had to bring out in the logic of Aquinas’s argument is his assumption that predicates signify forms and that the truth of sentences is a matter of the actuality or inherence of those forms in the subjects of predication. This notion, the “inherence theory of predication,” is a central element of what historians of philosophy call “realist” semantics. The fate of realist semantics is a complicated story but the short version is that significant thinkers after Aquinas rejected this account of language, and proposed an alternative, account, which we may call “nominalist” semantics. In accounts of the history of philosophy, the dispute between realism and nominalism is often described as a metaphysical one, about the “status of universals,” whether or in what sense universals, as opposed to particulars, exist. But realism vs. nominalism is actually much better characterized as a logical or semantic dispute, about how words signify truth, and the role of forms and their explanatory function in cognition and signification.

Within the realist semantic framework, the everyday, pre-philosophical notion of a distinction between substantial and accidental changes helped to articulate a natural fit between a metaphysical account distinguishing between substantial and accidental modes of being, and a logical, conceptual, or semantic account, distinguishing true substantial and accidental predications, mediated in terms of the inherence of substantial and accidental forms. The nominalist alternative, eliminating the role of forms, thus inadvertently eliminated a ready way to talk about modes of being and truth and their connection, which made possible the neglect of the distinction between substance and accident as modes of being and modes of truth.

As a result, one of the long-term legacies of nominalism has been the diminishing significance, or even the utter neglect, of the notion of “substance” in philosophy. Metaphysics, for instance, was once unified and defined as a science in terms of the primary mode of being, substance. But what gets called “metaphysics” in modern analytic philosophy today is often conducted without any notion of substance at all, and as a result is usually not described as a science with any unified subject but as an historically arbitrary collection of questions about identity, time, modality, etc. Ironically, a version of a “metaphysical” question about of “the status of universals” persists, but unmoored the concept of substance, from the notion of forms as objects of signification and actualizing causes, and from the original semantic framework which originally gave rise to the question.

Without elaborating on the nominalist perspective, suffice it to say that the question of the truth of the statement This is my body, said of the Eucharist, does not in a nominalist analysis lead to any of the conclusions, or give rise to any of the questions, that it did for Aquinas on a realist analysis. This does not mean that a nominalist cannot have an orthodox understanding of the being of Christ’s body in the Eucharist, it only means that that understanding would feel, and actually would be, logically unconnected to and wholly incidental to, a conceptual analysis of the truth of the words of consecration. While for Aquinas, on a realist analysis, the doctrine of transubstantiation quite naturally unfolds from an analysis of the truth that The Eucharist is the body of Christ, on a nominalist analysis the doctrine of transubstantiation necessarily, and in fact historically, looks rather arbitrary, only one among many possible accounts of Eucharistic presence, and one based on the imposition of technical philosophical categories that may have no connection to Biblical or early Christian discussions of the Eucharist.

Indeed, from this nominalist perspective, rather than the questions that arise for Aquinas about the mode of being of Christ in the Eucharist, a different set of questions would arise, and indeed some of the very questions that I earlier described as the expected questions of a typical modern reader of the Summa, questions which we can now see would need to be reformulated or redirected from the perspective the realist conceptual framework that Aquinas would have taken for granted:

Is it appropriate to use Aristotelian philosophical categories, especially substance and accident, to interpret the Eucharist? The realist would respond that such categories are not distinctively Aristotelian but rather natural, common, pre-philosophical concepts that Aristotle only helped to articulate and expound.

Is transubstantiation the only way to articulate the orthodox understanding of Christ’s real presence in the Eucharist? The realist would respond that “real presence” is and always has been an inadequate summary of the Church’s teaching about Christ’s presence in the Eucharist, and that it is more historically and theological accurate to insist on Christ’s substantial being in the Eucharist, a kind of “presence” for which the doctrine of substantial conversion, that is “transubstantiation,” is uniquely fit to defend.

Do we even need to have a metaphysical account of the Eucharist? If having a “metaphysics” means having a theory, no you don’t need a special theory, and the great 20th Century Catholic philosopher Elizabeth Anscombe was right that it is at least as pedagogically important for worshipers to observe reverent practice in receiving the Eucharist than for philosophers articulate accurate conceptual analysis of the Eucharist’s metaphysical status (G. E. M. Anscombe, “On Transubstantiation,” The Collected Philosophical papers of G.E.M. Anscombe, Vol. III, Ethics, Politics and Religion [Oxford: Blackwell, 1981], pp. 107-12). But if having a “metaphysics” means having the ability to make judgements about reality, including not only judgments about whether things do or don’t exist but how they exist and the different, related modes of being by which things can be said to exist, then yes obviously the Church’s teaching on the Eucharist, starting with Jesus’ own insistent words in the Gospel of John, and formally summarized, encapsulated and proclaimed through the teaching on transubstantiation, certainly demands that the faithful—and not only faithful philosophers and theologians—“have a metaphysics” about the Eucharist.

VII. Conclusion: The Reciprocal Gift

I said at the beginning that in turning to Aquinas on transubstantiation I wanted to help recover the role that substance, and the signification of words, play in his conception of the metaphysics of Eucharist. As an exercise in reading and thinking about Aquinas’s treatment of the Eucharist, and reconstructing the conceptual framework of “semantic realism” in which he formulated and answered his questions, I tried to anticipate the kinds of questions that readers today might bring to the Summa Theologiae, and allow those questions to be challenged, displaced, or redirected by the questions Aquinas himself asks and answers there. I also said that my goal was not primarily to defend the truth of the doctrine of transubstantiation, but rather to defend its intelligibility, to help you appreciate that Aquinas, in defending it as true, draws on a coherent account of language and causality that, before coming to Aquinas, we might not have shared or found easy to access or articulate.

Of course I do hope that a philosophical lecture on metaphysical and logical first principles helps you appreciate the power and fecundity of the Eucharist. Whether this conceptual exercise helps you personally in your spiritual life, or whether it has potential to foster more fruitful ecumenical dialogue with other Christians, I will leave as questions for you to ponder and explore. But at the very least, I hope that you can now better appreciate why, from Aquinas’s perspective, Aristotelian conceptual resources would be received as a kind of Providential gift, helping the Church better to articulate a mystery of faith. That gift, especially attention to the notion of substance and the accompanying account of signification and predication in terms of formal causality, was prized by Aquinas and, thanks to him, has come to prized by the Church.

I have taken for granted that that gift has had a rocky subsequent history, sometimes neglected, unappreciated, or even forgotten in theological, cultural, political, and ideological confusions. If the argument of this lecture has been successful toward fostering appreciation of that gift, if you have found it worthwhile to follow these reflections argument, to try to interpret and understand the questions that were once asked and the conceptual framework from which they were asked, that means that today, 750 years after the death of St. Thomas, we can now experience the Church’s persistent insistence on the doctrine of “transubstantiation” as itself a reciprocal gift back to philosophy—and even an act of philosophical memory. By its continuing, unequivocal, and apparently anachronistic attachment to substantial conversion and “transubstantiation” as an account of Christ’s “presence”—or better, His being—in the Eucharist, Catholic dogma has staked out a strong defense of the role of substance for the formation of judgments of truth, including about who we are, our nature, and our destiny. So even in proclaiming the mystery of Eucharistic conversion, and especially thanks to the great theologian Saint Thomas, the Church invites authentic dialectical inquiry in pursuit of understanding, ensuring that vitally human conceptual resources, however temporarily obscure, need never to be altogether forgotten. Thank you.

Note: Readers interested in fuller scholarly exploration of the main arguments of this lecture can see two publications by the author: “Substance Made Manifest: Metaphysical and Semantic Implications of the Doctrine of Transubstantiation,” Saint Anselm Journal 9.2 (Spring 2014), and “‘Real Presence’ Is Not Enough: Reclaiming the Lost Semantics of ‘Transubstantiation,’” in Gyula Klima, ed., The Metaphysics and Theology of the Eucharist: A Historical-Analytical Survey of the Problems of the Sacrament (Springer, 2024), pp. 433-454.



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