In this article we will review these three concepts and the relations among them by giving examples from the realms of both physical and metaphysical concepts.
Even though there is no universally accepted definition of analogy, or metaphor, or literal similarity, the purpose of their use is unanimously defined as "throwing light on an unfamiliar concept or situation using a familiar one." The past few decades have witnessed several attempts of redefining these terms or at least extending a definition that is somewhat agreed-upon to an all-encompassing one. In so doing, researchers tended to employ mathematical structures that are by no means simple. What seems to differ from one approach to another is the method used in the process of establishing a correspondence between the familiar and the unfamiliar. Our purpose is not to give a full account of these approaches here, as there are so many of them, but rather to adapt one that is more convenient for conveying our examples.
Analogy: The word analogy is derived from the Greek word analogia. Originally, this was a mathematical (actually a musical) term before becoming a grammatical and linguistic one, meaning "proportion" (Szabo 1978, 23). An example of Aristotelian analogy is "spine is to fish as bone is to animal." This simple analogy is generally formulated as A:B = C:D. We say, in this case, A and C are analogous. The sense in which A and C are analogous could be a property they have in common as well as the similarity between their relations to B and D, respectively. In the spine and bone example above we observe both. In the analogy "feet are to animal as wheels are to automobile," however, feet and tires have virtually nothing in common, but they are analogous with respect to their functions within the bodies that they are part of, i.e., both are used as a means of transportation. Therefore, common relations are essential to analogy, but common objects are not. (Gentner-Markman 1997, 46).
One of the recent approaches to analogy which is widely used is the structure-mapping theory (SMT) (Dedre Gentner, 1983). It presumes a mapping between the familiar (domain or base) and the unfamiliar (target). The domain and the target consist of objects and relations among objects. SMT establishes a one-to-one correspondence between the objects of the domain and the target in a way that preserves the relations between objects (Those who are familiar with the category theory in mathematics will notice the resemblance of this mapping to a "covariant functor" between two "categories"). This is a "structural alignment" between the domain and the target (Gentner-Markman 1997, 47). In the "feet and wheels" example the mapping occurs between a body and an automobile. It maps feet to wheels and the relation TRANSPORT (feet, body) to the relation TRANSPORT (wheels, automobile). One can find more matching elements between a body and an automobile. For instance, we can match the heart of the body to the engine of the vehicle and observe that the relations RUN (heart, body) and RUN (engine, automobile) are preserved.
One might ask where do the arms get mapped? The answer is "nowhere." We do not expect this mapping to match every object in the domain to an object in the target. The "power of the analogy" is not in the number of objects that are matched or the common attributes that the objects share. It is rather the degree of matching among relations that makes an analogy more powerful (Gentner 1982, 110).
Having introduced the concept of analogy by using some simple physical examples let’s now consider a not-so simple metaphysical situation.
In the 1920’s two mathematicians proved a very interesting but at the same time very puzzling theorem, known as the Banach-Tarski Paradox. In plain English, the theorem states that it is possible to divide a solid ball into a few pieces and reassemble those pieces together to make two balls, each of which has the same size as the original ball that was divided. A more striking consequence of their theorem is (you may want to sit down before you read this) a solid ball the size of a small pea can be cut into a number of pieces and reassembled into a new ball the size of the sun! Strange as it may sound, it is a valid mathematical argument, not a myth. (We have to note that it is not something one can do at home using a knife and a cutting board, because some of the pieces have no volume!) The analogy that we would like to establish under SMT is to map that solid ball of the theorem to a small amount of water which could quench the thirst of an army of about 30,000 in Tabuk in year 631. This was a miracle given to Prophet Muhammad, peace be upon him. A similar miracle of Prophet Jesus, peace be upon him, is described in the Bible, Matthew 14:21 (Volker Runde, in the Sky 2 (2000), 13–15).
Metaphor: The essence of metaphor is understanding and experiencing one kind of thing in terms of another. (Lakoff & Johnson 1980, 104) Simple examples are "What a sweet baby!" "Your car is a lemon, let’s take mine." Obviously babies are not candies, nor are vehicles some sort of fruit. We use this sort of "identification" in order to communicate our ideas/feelings in a more striking way. Here are more examples of metaphors: "he is the apple of my eye," "it’s raining cats and dogs," "he has a golden heart," "she cried rivers" etc. As these examples show, the distinguishing characteristic of metaphors is substitution, for example, rivers taking the place of tears in the last example. And this substitution takes place between different domains. If we say "a nightingale is a bird," that’s not a metaphor; it’s a literal categorization, as both nightingale and bird signify the same domain (Gentner 2005, 200).
As long as the correspondence is not purely attributional, but some relations are also preserved we can also talk about structural alignment for metaphors (Gentner 88, 49). From this perspective, many metaphors are in fact analogies, but it’s the form of the language that helps us differentiate them. For example, "the engine is the heart of an automobile" is a metaphor, but it uses the same structural alignment of the analogical comparison that we mentioned above.
Nonetheless, not every metaphor is of this sort. Consider, for example, the verse (48:10) "God’s hand is over their hands" from the Qur’an; this was revealed in connection to some 1,400 believers’ pledging allegiance to Prophet Muhammad, peace be upon him, under a tree in Hudaybiyah in year 628 by giving their hands to him. Whatever "God’s hand" in this verse refers to, whether it is to His power, His victory, His protection and blessings for the believers, or His acceptance of their pledge, it is far from being a physical hand. Therefore, we can not imagine a relation between dissimilar objects (Gentner 1982, 109; Gentner 2001, 204) that is mapped to the relation (Hand, God) under a structural alignment using SMT.
Literal similarity: If there is a considerable number of common attributes that are shared by the objects of the domain and the target then the comparison is more likely to be a literal similarity (Gentner 1982, 110). For example the comparison in the following verse of the Qur’an is a literal similarity: "Indeed, the example of Jesus to God is like that of Adam. He created him from dust; then He said to him, "Be," and he was" (3:59). In this example there are a great number of attributes that Jesus and Adam (peace be upon them) share but only one of them is the subject of the comparison here, which is that both Jesus and Adam had no father. If Jesus also had no mother this would be an "identity," not a similarity (Gentner 1982, 110).
The statement "Jesus is like Adam" makes much more sense than "Jesus is Adam," even if we make it clear in what sense we use this identification. Typically metaphors use the word "is" and literal similarity comparisons (similes) use either of the words "like" or "as." Mathematically speaking, if metaphors are equalities, then similes are approximations (Casnig).
Even though metaphors are substitutions, they are not necessarily "two-way" identifications. In other words, most of the times they are asymmetric; i.e., there is a sense of direction in the "identification." For example, we never substitute a car in the place of a lemon and say "this lemon is a car." This is because the first and foremost requirement of any comparison is that it be informative. What information do we obtain from the statement "rose is love" or "iron is fist"? In that respect many metaphors are irreversible, like similes: "a butcher like a surgeon" is quite different than "a surgeon like a butcher." One is a compliment but the other is not! (Gentner 2001, 224). Perhaps irreversibility can also be taken as a distinguishing character of (at least attributional) metaphors.
Mathematical and metaphysical examples: Although there is no consensus on how mathematical ideas come about, it is certain that they are introduced into our world of knowledge by symbolism. Whether we associate a symbol to something physical, such as the symbol 70 to the weight of an object or the letter g to gravitational force, or to an abstract mathematical concept, such as the letter i to √–1, we are substituting one thing to mean another thing. We even associate symbols to concepts we cannot even describe, such as the concept of infinity and the symbol ∝that is used to represent what it signifies in mathematics. From this perspective, mathematical symbols can be viewed as metaphors (Pimm, David 1981).
On the other hand mathematical formulas preserve the relations among the objects or concepts that they represent. In that respect, it is possible to see them as analogies as well. Therefore, they can be subjects of structural alignment. In the next example we will use SMT to form an analogical comparison between infinity and human life in order to better understand a Qur’anic verse.
In verse (5:32) of the Qur’an reads: "…he who kills a soul unless it be (punishment) for murder or for causing disorder and corruption on the earth will be as if he had killed all humankind; and he who saves a life will be as if he had saved the lives of all humankind…"
In a sense this verse means "one equals many." How can that be? How can one be equal to a million? Or a billion? Those who know something about mathematics with infinities will remember that it is a quite different thing from mathematics with ordinary numbers. For example, if we add two infinities we still get infinity, i.e., ∝+∝=.∝=∝, something that never happens with any finite number, except for 0 (0+0=2.0=0). Likewise, if we add any number of infinities together we still get infinity: ∝+∝+∝+...∝=∝.Therefore, for any positive number m if we write m.∝=∝ it would be a perfectly acceptable mathematical statement.
Now, everyone will agree that there is no value one can associate to human life. Therefore, it’s fair to say that the value of human life is infinite. Let’s map "∝" to "saving the life of one person" under a structural alignment and let counting people in the target correspond to adding infinities in the domain. Now, if m represents the total number of lives on earth then what element should we associate to saving them altogether? The answer is m infinities added together, in other words m.∝ But seeing that m.∝ is equal to ∝ we can say that saving the lives of all people on earth is no different than saving the life of one individual! That’s how one can equal many. Now, if we map "killing an innocent person" to "–∝" then we clearly see that the mathematical statement m.(-∝)=-∝translates into "killing all innocent people on earth is as grave a sin as killing one."
Note that this "one equals many" situation is not a violation of the requirement that structure mapping be one-to-one (Gentner-Markman 1997, 47). It’s a relation that occurs between the objects of the domain and the objects of the target and that relation is preserved under a one-to-one structure mapping.
Another relation between infinities is that "∝-∝" is indeterminate. In particular "∝-∝" is not necessarily 0. Using the analogy we just constructed we can translate this as "killing one innocent person and saving the life of another does not balance out." Then, "∝-∝"is indeterminate" translates as "we cannot know if God will forgive that person for saving a life or punish him/her for taking one; it depends on which ∝is greater!" Indeed, those who have taken calculus will remember that "∝-∝" sometimes turns out to be a positive number and sometimes a negative number; as well as 0 or ∝ or -∝
One could ask, what about m.0=0? Isn’t this also true? Yes, indeed "the sum of m zeros is equal to zero" is another mathematically accurate statement. Then, what meaning could this equation be given? Perhaps this would be the "murderer’s" version of the Qur’anic principle that we mentioned above: "When the life of an individual has "no value" in your heart, killing one person or a million people should be equally disheartening (!)"
Another mathematical tool that would be helpful in interpreting the above-mentioned principle is a technique that is used in mathematical proofs. When proving a fact about a set of elements in mathematics one proves it for an arbitrarily chosen member of the set and it is automatically generalized to the rest of the elements in the set. For example, in order to prove the statement "the square root of every prime number is irrational" we choose a prime number, say p, arbitrarily and prove the statement for it. Once we do that it is as if we proved that √2 is irrational, √3 is irrational, √5 is irrational etc. It covers all the numbers in the form √p, where p is a prime number. In the same way, when one kills an innocent person the message that it is acceptable to kill "any" innocent person is given, as the choice of person has been made arbitrarily. Therefore, this can be likened to killing all of mankind because being able to kill one person is simply generalized to all people who could be in that person’s shoes.
Summary: In this article we have given examples of analogy, metaphor, and literal similarity and have tried to indicate some distinguishing characters that set them apart. We included some uncommon metaphysical phenomena which have been placed in analogical correspondence with mathematical quantities with the intention of showing that mathematics can be used to shed light on purely religious concepts as well.
Yusuf Ziya Gurtas is an assistant professor of mathematics in Queensborough Community College, CUNY.
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