I. Introduction: Words and their Meanings

The poet writes: “You know sometimes words have two meanings.” Upon reflection, each of us can think of many examples of this familiar phenomenon. For example, the word “bark” can mean the outer surface of a tree, or it can mean the call made by a dog. The word “pen” can mean a kind of writing utensil, and it can mean an enclosure such as a pigpen or a playpen. Sometimes a word has different meanings because of its use in scientific, business, legal, or other specialized contexts. “Law” means something different in physics than in politics. “Strike” means something different in business, bowling, and baseball. “Ball” means something different within baseball itself (i.e., both the sphere used to play the game and an umpire’s judgement about whether an individual pitch is a “ball” or a “strike”). “Pitch” means something different in baseball and soccer. I was asked at a doctor’s office who my “medical provider” was, and I had to ask if “provider” meant the insurance company or a physician. So, the poet speaks truly: sometimes words have multiple meanings.

But what does it mean for words to have two meanings? Why is this significant, and how does analogy fit into all of this?

Let’s begin with what it means for a word to have two meanings. To grasp this, we need to consider first what it is for a word to have meaning at all. The fourth- century B.C. philosopher Aristotle gave us a useful tool for thinking about the meaning or (to use the technical term) the signification of words. Propositions combine words or terms into truth claims in which some predicate is affirmed or denied about some subject, as in “The pen is blue” or “The bark is not smooth.” The words or terms themselves are signs of the speaker or writer’s thought or conception of the things being discussed. More precisely, the words are signs to the listener of a speaker’s mental conception, and the speaker’s mental conception is a sign of the nature of the things the speaker is speaking about.{1} Words signify things or the natures of things, but only insofar as both word and thing relate to the speaker’s conception. For a word to have two meanings is for a speaker to be able to use the same word to signify through different conceptions the natures of different things.

The technical term for using the same word to signify things through different conceptions is equivocation. “Bark” is said equivocally of a dog’s call and a tree’s surface. “Right” is said equivocally about a side of a body, a political orientation, a legal entitlement, and an answer to a question. “Pen” is said equivocally about an enclosure and a writing utensil. By contrast, the technical term for using the same word to signify things through the same conception is univocation. Two calls made by a dog (or by different dogs) are called “bark” univocally, and two surfaces of trees are also called “bark” univocally. The correct answers to two different questions are called “right” univocally to one another. In baseball, the throwing hand on a second baseman is called “right” univocally to the throwing hand on another second baseman. All three numerically distinct pitches leading to a “strikeout” are “strikes” univocally.

Now, what if the poet had spoken with greater precision and had written instead, “Sometimes two or more meanings of a word are related to one another, and sometimes the different meanings of a word are not related”? Returning to our examples of “pen” and “bark,” there is no apparent relation between the meaning of “pen” as in a writing utensil and “pen” as in an animal enclosure, nor is there any apparent relation between the bark of a dog and the bark of a tree. Knowledge of one of these meanings of “pen” or “bark” provides no insight into the meaning of the other meaning that is equivocal to it. In such cases as these, the technical term applied is pure equivocation or, alternatively, these cases are said to be equivocals by chance—because there is no reason behind why the same word should be applied to these different things. Note, there can be historical reasons for why a word took on a meaning that is purely equivocal in relation to its previous meanings. The word “right” may have taken on a political meaning due to where a group of French politicians sat relative to other French politicians in the same room, but the place where a politician sits relative to other politicians in a room is not part of the meaning or signification of “right” as applied to political views. There is nothing incongruous about holding right wing political views while sitting in what is physically the left wing of a room in a legislative building.

Contrast these examples of pure equivocation with my earlier example of “provider.” The physician and the medical company are not “providers” in the same sense. After all, the physician provides care informed by the art of medicine, and the company provides physicians as well as space, equipment, and staff supporting the practice of medicine. Yet, there is clearly a connection or relation between what makes the physician and the company “providers” in their own ways such that knowledge of one would not be altogether irrelevant for knowledge of the other.

Consider also how we speak of a “length” of time and a “length” of a body or of a physical distance of some sort, as in “The lecture is thirty minutes long” and “The pants are thirty inches long.” Here again, “long” or “length” are not said univocally of a time and a spatial magnitude, but neither are the meanings purely equivocal. From knowing what “length” signifies about a magnitude we can begin to acquire insight into a “length” of time and vice versa. Indeed, we use terms that signify physical magnitudes with different but not altogether unrelated meanings all the time. Just to give a few examples, we speak about “hard” rocks and “hard” tests; about “rough” terrain and “rough” play and “rough” days; about “sharp” edges, “sharp” sounds, “sharp” smells, and “sharp” remarks; about “materials” for building and “materials” for an argument (and, in team sports, about billboard “materials”); about “building” furniture and “building relationships;” about “grasping” someone’s hand and “grasping” the point of someone’s remarks; and about the “point” of a sword and the “point” of owning something or of reading about analogy. For practical purposes, we cannot get by in life without using words with different but related meanings. The technical term for this sort of equivocation is equivocation by design or deliberate equivocation because there is a reason or explanation behind why the same word is applied to the different things that it is applied to—even though the word is not signifying the same nature in the things that it names as though it were being used univocally.

Equivocation by design is also called analogy, and analogy is considered to be a kind of middle between univocation—where the word picks out the same nature in different things—and pure equivocation—where the name does not signify anything that the things share in common, and it is only by the oddities of the history of a language that the things share the same name at all.

So, we now have three technical terms for the three ways of using the same word to talk about different things: (1) when a word is said about different things with the same meaning (signifying the same nature in the different things), then it is said univocally. (2) when the same word is said about different things with different and unrelated meanings, then it is said purely equivocally. And when (3) a word is said about different things with different yet related meanings, then it is said about them analogously.{3}

What makes reflection on words and their usage important? Let’s begin with univocation. There is a great benefit to things being univocal to one another, namely, that what is true of one is true of the other insofar as they are univocal. Anything that you learn about the nature of the bark of a tree, is true about everything else that is called “bark” univocally. (Assuming no misidentification has happened.) Hence, the tree scientist does not need to have studied every individual tree bark sample that has ever been in order to know something about all of them and, thereby, to be able to say things that are always and everywhere true about the nature and properties of tree bark. By contrast, no amount of study of tree bark will provide the scientist with insight into the nature and properties of the call of a dog, and the science of dogs provides no insight into tree bark. For example, speaking of the bark of a dog, one can say, “barks put humans on alert.” However, one cannot proceed to argue, “A bark puts humans on alert; a tree grows bark; therefore, a tree grows something that puts humans on alert.”

The general point here is that univocation makes our reasoning secure and valid, whereas pure equivocation does the opposite. Univocation is useful for learning and scientific discourse. Equivocation must be avoided with the utmost care by the scientist or by anyone trying to engage in rational thought. Indeed, as Aristotle explains in the Posterior Analytics, his work on the theory of demonstrative science, the reason why scientists do not fall into error by accidentally using words equivocally in their arguments is that they define their terms, and their demonstrations proceed through the definitions of their terms. (See especially Thomas Aquinas, Commentary on the Posterior Analytics, Book 1, lecture 22.) I will return to this point in the following section on Analogy and Aristotelian Science.

II. Analogy and Aristotelian Science

Every science (especially, but not only, science in the Aristotelian tradition) seeks to draw affirmative conclusions about its subject and/or the essential parts of its subject. The biologist aims to draw conclusions about living things in general and about plants, animals, and their species (the essential parts of biology) more specifically. The geometer aims to draw conclusions about figures in general and three-dimensional and two-dimensional figures and their species more specifically. For natural theology, whose subject is God as knowable by human reason, the goal would be attained in a demonstration which concludes that “God is spiritual,” or “God is intellectual,” or “God is wise,” or “God is good,” etc.

In Aristotelian science, demonstration (in the strictest sense) occurs through a syllogism or set of syllogisms. A syllogism is a form of logical reasoning whereby two statements or propositions that are (a) known to be true and (b) overlap in a common term, called the “middle term,” (c) generate knowledge of a third proposition which (i) lacks the middle term but (ii) uses the remaining non-overlapping terms (called the minor term and the major term) for its subject and its predicate. Hence, to use a variation of the classic example, one reasons syllogistically from (1) “All animals are mortal” and (2) “All humans are animals” to the conclusion (3) “All humans are mortal.”{4}

Of interest to the topic of analogy in natural theology is that, in a demonstrative syllogism, the middle term must be the definition that signifies what-it-is-to-be (that is, the essence or nature of) the subject. In the absence of this definition, no syllogism or chain of syllogisms will establish a necessary connection between the subject and predicate of its conclusion such that what-it-is-to-be the subject causally requires the subject to possess the predicate (or to not possess the predicate in the case of negative demonstration). And if a subject can exist without also being the subject of that predicate, then the subject only has that predicate incidentally. What belongs to a subject merely incidentally cannot be demonstrated of it.{5}

Why does this matter for theology, either natural theology or revealed (sacred) theology? For God to be the subject of the conclusion of a demonstrative syllogism, the definition of God needs to be the syllogism’s middle term. And not just any sort of definition will do. The definition that serves as a middle term in a demonstrative syllogism must signify the very essence of the subject of the demonstration, in this case, the nature of God. Such definitions apply only to terms signifying a species, and they give the genus of the species and the difference that sets it off from the genus itself and other members of the genus. (Minimally, such a definition would express some of the genus or the difference of its species.{6})

For God to have such a definition, the word “God” would have to signify not only a nature or essence (as St. Thomas Aquinas says that it does), but it would have to signify the essence of a species under a genus. If God were a species under a genus, then God would have something essentially in common with creatures just as humans have something essentially in common with beavers (animality) and with oak trees (being alive) and with rocks (bodiliness) and with angels (substantiality). As the examples above illustrate, terms that signify the essence of a species under a genus are said univocally about each species under the genus and about each individual under the species. Plato and Aristotle are univocally humans; humans and beavers are univocally animals; humans, beavers, and oaks are univocally living; and humans, beavers, oaks, and rocks are univocally bodies. But nothing whatsoever belongs univocally to God and creatures (for reasons which will be treated below in the section Analogy and Scientific Discourse).

Consequently, scholastic theologians deny both that definitions signifying what-something-is can be applied to God and that any demonstrations through such definitions can be made about God. Instead, they reason that only a lesser sort of demonstration can be made about God, one in which an effect of God (such as “causing motion first”), or a relation to creatures (such as “greatest being”), plays the role of a definition in a demonstration of the existence and the attributes of God.{7}

III. Analogy in Scientific Discourse

As discussed above, we can engage in scientific discourse (and other forms of rational thinking) by using words univocally but cannot by using words equivocally. What about analogy? When we use words analogously, can they be useful for learning and discourse like when we use words univocally? Or do words used analogously have the same effect as words used equivocally, invalidating any arguments in which they appear? It is this question that vexes us when finding words to talk about God.

Whether we say, “God is good,” “God is wise,” “God is better than pizza,” or “God is love,” whenever we talk about God, we use words that we also use to talk about other things. If we do not, we either say nothing about God at all, or we only use words learned through direct intellectual encounter with the divine nature, unmediated by any experience of creatures. In the latter case, instead of saying, “God is good,” we will say “God” and the predicate will be a term signifying what we grasped from that mystical experience. But in the absence of such mystical experience or of suitably prepared dialogue partners, we are left to speak of God using words also used about creatures. This situation gives rise to the question: When we speak about God, do the words that we use signify (1) the same reality/essence/nature as they do about creatures, (2) something altogether different, or (3) something partially the same and partially different? To use our familiar standard terms from the Aristotelian and Scholastic traditions, do we speak about God and creatures (1) univocally, (2) purely equivocally, or (3) analogously?

If our words signify God univocally to how they signify creatures, then, evidently, we can use these words in valid reasoning aimed at discovering truths about God from truths already known about creatures. However, for our words to signify God and creatures univocally—that is, with the same meaning such that the words signify nothing about creatures that they do not also signify about God and vice versa—it would have to be the case that God and creatures are really no different with respect to what is said about them through the words being used. In effect, God and creatures would need to have the same nature or essence, either specifically or in some more generic way.

For example, consider the claim that “God is wise” or “God has wisdom.” We first learn about what wisdom is from the experience of wise humans in our lives or from reports of wise humans. It is part of our experience that some humans are wise and others are not. We find that wisdom is an acquired quality in humans. When we say something along the lines of, “Socrates is wise,” we are attributing a quality to Socrates that he does not need to have because he is human. Not all humans are wise, and no wise human is always wise or needs to remain wise as a condition of remaining a human. The loss of wisdom can only be an indirect cause of the loss of one’s humanity, even should one lose wisdom and humanity simultaneously, as when an unwise choice leads to one’s immediate death. There is a real difference between Socrates’s quality of wisdom and his human nature.

But what about God’s wisdom? If wisdom is said univocally in the propositions “God is wise” and “Socrates is wise,” then we would be making a valid argument if we say: “Wisdom is a quality, and God has wisdom; therefore, God has a quality.” We could go on to argue, “Something’s qualities can change; God has qualities; so, God’s qualities can change.” From there we could go on to make the further inference, “whatever changes is an effect of some other being that is its cause; God is something that changes; therefore, God is an effect of some other being that is God’s cause.” Since whatever else God is, God is not caused by any other being; we can see that the assumption that words signify God and creatures univocally leads to the absurd conclusion that “God is not God.”

The philosophers of the Christian tradition agree that God and creatures do not have a nature in common. Likewise, Orthodox Christian theology affirms the distinction between the human nature and the divine nature of Christ while also affirming that the same Divine Person is both God and human. God is an unchangeable source of being whose nature is not even generically the same as anything whose nature is capable of change or in any way dependent upon a source for its existence. Consequently, all philosophers in the broadly Aristotelian and Scholastic tradition either (a) deny that words apply to God and creatures univocally or (b) use the word “univocal” in a way that is equivocal to the way that others use the word “univocal” when they say that names can be said univocally about God and creatures (as in the case of Bl. John Duns Scotus, William of Ockham, and members of their traditions). Perhaps unfortunately, “univocal” is used equivocally and “analogy” is used analogously by different scholastic philosophers and theologians and even by the same scholastic philosophers and theologians in different places within their own writings. In any case, if by “God” we in fact mean the first causal source of creatures and their natures, then God’s nature must indeed be different from the natures of what God creates. The alternative is that whatever God creates is God too.{8}

The alternative to names or words being used univocally about God would be that they are used only purely equivocally about God and creatures. Whereas affirming that using names about God and creatures univocally leads into the error of denying the difference between God’s nature and the nature of creatures (and thereby effectively denying the existence of God altogether), the approach of saying that words only ever signify God and creatures purely equivocally rules out learning about God from what we know about creatures. The search for knowledge of the existence and attributes of God from what we know about creatures would be as futile as the search for insight into the existence and attributes of tree bark through the study of dog barks. “A bark is a sound that puts humans on alert, and bark grows on trees; therefore, a sound that puts humans on alert grows on trees” is clearly not a demonstrative syllogism. Moreover, the problem would not stop with natural or philosophical investigation of God. Revealed theology (what St. Thomas calls “sacred doctrine”) also uses words. Thus, even divinely revealed scriptures would give us no insight into God whatsoever.

So, our options are to claim either (a) God and creatures share the same nature; or (b) our words signify nothing about God in any way connected to what they signify about creatures and that, in fact, we are not saying anything meaningful when we use our words to talk about God; or (c) the words that we use to make true claims about God are used analogously to how we use those same words to make true claims about creatures. Option (a), that names are said univocally about God and creatures, rules out any distinction between God and creatures, and option (b), that names are said only purely equivocally about God and creatures, rules out learning about God from creatures.

But does option (c), that names are said by analogy of God and creatures, fare any better than the alternatives of univocation and equivocation? Aristotle affirms that demonstrations can occur using what things have in common by analogy even though such things do not share a common nature.{9} Unfortunately, Aristotle gives little account of why or with what restrictions this can occur. And, as is evident from examples, there must be some restrictions on demonstrations using analogous terms.

The classic example of failed reasoning leading to the fallacy of equivocation happens to employ a term analogously. An animal and a urine sample can both be called “healthy” via a kind of analogy that later scholastics call “analogy of attribution.” “Analogy of attribution” is the kind of analogy in which a relation to one of the things signified by the name provides the meaning of the name when it is said analogously about the others. The word “healthy” in the proposition “the animal is healthy” signifies that the animal’s organs and other parts are in good order. Using “healthy” in this sense, we can rightly say, “Everything healthy is alive.” Now, as said about a urine sample, “healthy” means that the sample comes from a healthy animal—the urine’s relation to the animal’s health provides the meaning of “healthy” as applied to the urine. These two analogous (by the analogy of attribution) meanings of “healthy” do not permit us to reason validly: “Everything healthy is alive; this urine sample is healthy; therefore, this urine sample is alive.” The same issue arises when we replace the example of urine in the minor premise with medicine. When “healthy” is said about medicine, the predicate “healthy” means that the medicine causes health in an animal. Accordingly, we again fail to have a valid syllogism if we argue: “Everything healthy is alive; this medicine is healthy; therefore, this medicine is alive.”

Consider also our example from before of length. Speaking of a magnitude, one can say, “a greater length requires a greater amount of space.” But the argument does not follow validly which says, “A greater length requires a greater amount of space; a minute is a greater length than a second; therefore, a minute requires a greater amount of space than a second.” This example illustrates that, although “length” is said analogously of magnitude and time, an argument from the properties of one sort of length to the properties of the others can be invalid.

Additionally, in speaking of a surface, we can say “what is rough is uneven.” But we cannot draw the conclusion, “what is rough is uneven; the day was rough; therefore, the day was uneven.” If we can draw this conclusion, it would only be because, just like the word “rough,” the word “uneven” is also used analogously about a surface and about a day.

I purposely use these examples of analogous length and analogous rough because, unlike the classic example of analogous health, they are analogous by the kind of analogy scholastic philosophers called “analogy of proper proportionality” (as distinct from “analogy of attribution”). This is significant because (a) Aristotle was talking about analogy of proper proportionality when he wrote that demonstrations can proceed on the basis of analogy and (b), following Aristotle’s example, major figures in the Thomist tradition, such as Thomas Sutton (d. 1315), Thomas de Vio Cajetan (d. 1534), and John of St. Thomas (d. 1644), single out analogy of proper proportionality as the only kind of analogy that can be used in a demonstration without falling into the fallacy of equivocation. The examples of “length” and “rough” in the previous paragraphs show, however, that analogy of proper proportionality can also fail to preserve valid demonstration.

So, does this about wrap things up for the possibility of talking about God in a meaningful way? The univocity option either turns God into another creature or creatures into God. The equivocation option renders our words into mere sounds signifying nothing when extended from creatures to God. Analogy can fall into the same logical pits as equivocation.

There is a way to save analogy and thereby preserve talking meaningfully and truthfully about God. First, we need to keep in mind that analogy is not supposed to be a kind of disguised univocity. Things that are analogous do not share the same nature—so what belongs to the nature of one need not apply in the same way to another and may not apply at all. Here I borrow an example from a Scotist critic of analogy. “Foot” is said analogously of a mountain and of a body part. As said of a body part, it can be said truly, “What has a foot can run.”{10} Yet we cannot argue validly, “What has a foot can run, a mountain has a foot; therefore, a mountain can run.” The reason why this does not work is that what makes both the part of an animal and the part of a mountain feet analogously is not that they are both moving parts. At least provisionally, I suggest that what makes them both feet analogously is that they are both sources of stability for the other parts. Their diverse analogous ways of “holding up” the other parts are their analogous similarity. This brings me to the second point. If we are going to draw any inferences about mountain feet from what we know of animal feet—if we are going to generalize from animal feet to something that would apply to mountain feet insofar as mountain feet are analogous to animal feet—it will have to be from what we know of animal feet precisely as a principle or source of stability. “If a foot falls, the whole-body falls” is a statement that applies both to an animal’s foot and to a mountain’s foot insofar as they are analogous. “What is rough is more challenging than what is smooth” applies both to rough terrain and to a rough day insofar as they are analogous. “What is wise knows ultimate causes and explanations” and “what is just gives to each what is due to them” applies to human and divine wisdom and to human and divine justice insofar as they are analogous. If I am right, then analogy does provide a way for talk about God that both avoids univocity’s reduction of God to creatures and equivocation’s reduction of speech about God to utter meaninglessness.

IV. Analogy and the Anti-Christ

The discussion above has shown that philosopher-theologians in the scholastic and Aristotelian traditions have been concerned that the names that we use to speak about God say too little about God for use in theology. In other words, there is a concern that analogy is too close to pure equivocation for use in theology or any scientific discourse. Scholastic philosopher-theologians, however, are also familiar with traditions of apophaticism or negative theology from the writings of Pseudo-Dionysius and Maimonides. This tradition warned of the dangers of thinking that one is saying more about God than one really is; that is, that analogy is too close to univocation. St. Thomas Aquinas’s work on names said of God and creatures reflects the apophatic tradition, notably in Summa theologiae (p.1, q. 13, a. 2), where he integrates the tradition of naming God by saying what God is not with practices of naming God through causal relations and naming God by adding eminence to what the name signifies (the actuality or perfection) insofar as it belongs to creatures.

In the twentieth century, Karl Barth expressed, in extreme form, the concern of the apophatic theologians that analogy compromises the distinction between God and creatures, saying famously that the analogy of being is the invention of the anti-Christ. This entry does not engage directly in apologetics for analogy against Barth as this is not the place for adequate treatment of his nuanced position or of the twentieth-century theories of analogy of being that Barth encountered. Important differences between Patristic apophatic theologians and the Protestant tradition influencing Barth are also beyond the scope of this article. Instead, this article observes the metaphysical and logical commitments assumed by a proponent of using analogy to speak about God and creatures, beginning with the metaphysical commitments.

To say that there is analogy between God and creatures is to affirm that there is nothing specifically or generically the same about the divine essence and the essences of creatures. Yet, there is more than mere verbal unity between what we attribute to creatures and what we attribute to God in such propositions as “God exists, and creatures exist,” “God is intelligent, and humans are intelligent,” “God is wise, and Socrates is wise,” and “the human soul is spiritual, and God is spiritual.” To borrow an example from St. Thomas, while a creature is wise by knowing the highest causes, God is wise by knowing Himself perfectly and through His essence. (See Summa contra gentiles Book 4, chapters 12 and 14.) The activities for which wisdom is predicated of the creature has nothing essentially in common with the activity for which wisdom is predicated of God. The former is finite and performed through an acquired habit that is really distinct from the nature of the creature. The latter is infinite and not really distinct from the divine essence itself or even from the highest cause which is the divine essence. The one is known to us from what it is—an acquired intellectual habit. The other is knowable to us only indirectly and though its effects. There is no more (indeed there is less) entailment of real specific or generic identity of essence between God and creatures in their wisdom than there is real specific or generic identity between times and places in their distances or lengths.

Just as analogy does not entail specific or generic unity between things, analogy does not entail that the speaker or thinker conceives of both things or their natures as though they were essentially the same, either specifically or generically. Although we first conceive of being, wisdom, justice, etc. through our experience of creatures, etc., when we come to apply those terms to creatures and to God with precision as to what we are saying (i.e. with the sort of definitions that allow us to avoid errors in reasoning brought on by equivocation and ambiguity), we come to realize that our concepts, which are derived from our experience of creatures, both (a) include elements that prevent them from being attributed to God without modification and (b) lack something that they should have to signify what God is. Hence, Aquinas writes that when we speak about God and creatures by analogy, we modify the definition of the words we use for creatures in two ways. First, we negate the part of the definition that entails imperfection. Second, we add eminence or excellence to make up for what is absent but needed for the word to signify God (ST, p.1, q. 13, a. 2 and 5). So, “wisdom” goes from (a) signifying that a creature has the quality or habit of knowing the highest cause to (b) signifying that God is essentially an unlimited knower of the highest cause. Bringing the metaphysics and logic of analogy together, we can say that the nature or essence of the analogous realities are not the same, and neither are the concepts through which the analogous realities are signified. There is no danger that recognition of analogy between God and creatures will lead one into idolatry—at least no more danger than there is that recognition of analogy between spatial and temporal lengths will lead one to think that they will travel across the room just by waiting for time to pass.

V. For Further Study

This essay presents analogy from a Thomist perspective. For insight into how many of the same philosophical issues arise and are treated in other influential twentieth- and twenty-first century schools of thought, see the study by Kris McDaniel, The Fragmentation of Being (Oxford University Press, 2017). Although the author does not point this out himself, McDaniel’s study displays the recapitulation of many scholastic disputes over analogy in the debates between phenomenologists, analytic philosophers, and other non-Aristotelian schools of thought.

For an overview of the history of the development of analogy in scholastic thought up into the late medieval/early modern period, see “Medieval Theories of Analogy” by E.J. Ashworth and Domenic D’Ettore in the Stanford Encyclopedia of Philosophy. This entry includes a bibliography useful for further study. As an introduction to contentious issues in the interpretation of the thought of St. Thomas about analogy, St. Thomas Aquinas on Analogy: A Textual Analysis and Systematic Synthesis (Loyola University Press,1960) by George Klubertanz remains an excellent source. More recent influential studies that take up many of these contentious issues (and take opposing sides on them) include John Wippel’s The Metaphysical Thought of St. Thomas Aquinas (Catholic University of America Press, 2000) and Steven A. Long’s Analogia Entis: One the Analogy of Being, Metaphysics, and the Act of Faith (Notre Dame Press, 2011). Notably, Wippel defends a developmental thesis whereby Aquinas’s mature writings do not employ analogy of proper proportionality. Long, on the contrary, defends the significance of analogy of proper proportionality for Aquinas’s doctrine. Wippel’s work is also a strong representation of the tradition that emphasizes the importance of the effect-to-cause relationship of creatures to God in establishing analogy between God and creatures.

There has also been significant work done on the critical position of John Duns Scotus towards analogy. Useful studies for someone entering the metaphysical thought of Duns Scotus include The Transcendentals and their Function in the Metaphysics of Duns Scotus (Franciscan Institute, 1946) by Alan Wolter and The Singular Voice of Being (Fordham, 2019) by Andrew LaZella. For studies addressing Thomist approaches to analogy that are informed by Scotus’s criticisms of the use of analogy in demonstrative arguments, see Joshua Hochschild’s The Semantics of Analogy (Notre Dame Press, 2012) and Analogy After Aquinas (Catholic University of America Press, 2019) by Domenic D’Ettore.

Karl Barth’s critique of analogy in theology is the subject of the volume, edited by Thomas Joseph White, entitled The Analogy of Being: Invention of the Antichrist or the Wisdom of God? (‎Wm. B. Eerdmans Publishing Co., 2nd edition, 2010). The series of essays in this volume provide a helpful entry into the background of Barth’s critique, Barth’s own position, and several responses to him.

VI. Summary Conclusion

Analogy is opposed to univocity at one extreme and to pure equivocation at the opposite extreme. When words signify the same things or natures through the same concepts, there is univocity and, because of univocity, security in reasoning. When words signify different things or natures through different and unrelated concepts, then there is pure equivocation and, with it, an insecure foundation for reasoning. In analogy, words signify different things or natures, yet these things or natures are not unrelated. The ways in which these analogous things or natures relate provides the foundation for different sorts of analogy; accordingly, the analogy can sustain or fail to sustain valid reasoning.

Analogy between God and creatures is necessary for theology because God’s essence and the essences of creatures cannot be the same even in a generic way, for that would make creatures into God or God into a creature. Nonetheless, the divine essence and the essences of the creatures must not be so unrelated that learning about God from creatures is impossible. Because God causes creatures, a creature’s nature or essence is related to God’s. This relation of creatures to God provides the opening for both human reason’s unaided discovery of the existence and attributes of God in philosophy and for God to reveal Himself to humans through creation and in the words that humans use to express what God has revealed to them.