B. N. Waller - Classifying and analyzing analogies.pdf - Logika nieformalna - dr_vanini

Classifying and Analyzing Analogies

Youngstown State University

BRUCE N. WALLER

Abstract: Analogies come in several forms

that serve distinct functions. Inductive anal-

ogy is a common type of analogical argu-

ment, but critical thinking texts sometimes

treat all analogies as inductive. Such an

analysis ignores figurative analogies, which

may elucidate but do not argue; and also ne-

glects a priori arguments by analogy, a type

ofanalogical argument prominent in law and

ethics. A priori arguments by analogy are

distinctive, but--contrary to the claims of

Govier and Sunstein-they are best under-

stood as deductive, rath«r than a special form

of non deductive reasoning.

Resume: Les analogies ont differentes formes

et fonctions. L'analogie inductive est une forme

courante d"un argument par analog ie, mais des

manuels de pen see critique traitent parfois

toutes les analogies comme si elles etaient

inductives. Une teUe analyse ignore les analo-

gies figurees, dont la fonction est parfois

d'elucider et non d'argumenter. Cette analyse

ne tient pas compte aussi des arguments a

priori par anaJogie, qui s'empJoient souvent

en droit et en ethique. Les arguments a priori

par analogie constituent une autre forme

distincte d'analogie, et contrairement it I'avis

de Govier et de Sunstein. its sont deductifs

plutOt qu'une espece speciale de raisonnement

non-deductif.

Keywords: Analogy, deductive, figurative. inductive. T. Govier, legal realism, C. Sunstein.

When disputes turn from ad hominem attacks and strawman distortions toward

serious argument, there is no better means of convincing listeners and settling

debates than by effective use ofanalogies. Unfortunately, it is often supposed that

all analogies can be covered with a single analysis. The result is that round analo-

gies are forced into square holes, and a powerful but complex form of reasoning is

oversimplified. The first step in understanding analogies is recognizing that they

come in several varieties and perform distinct functions. Evaluating one type of

analogy by the standards for another makes legitimate analogies appear fundamen-

tally flawed.

This paper will examine three types of analogies: figurative, deductive, and

inductive. Failure to distinguish among these has resulted in several problems in

the critical thinking literature. First, figurative analogies have been neglected, and

when noted at all they are frequently treated as flawed inductive arguments by

analogy. Second, the tendency to treat all analogies as inductive arguments means

that deductive arguments by analogy are either ignored or analyzed as ifthey were

inductive arguments. Misrepresentation of deductive arguments by analogy is

©lnformal Logic Vol. 21, No.3 (2001): 199-218.

200

Bruce N. Waller

also the source of the third problem to be examined: Trudy Govier's influential

denial of their status as deductive arguments. By emphasizing the often-tentative

nature of the principles invoked in unpacking deductive arguments by analogy,

Govier offers important insights into their structure; but denying their deductive

status obscures the way such analogies function in argument. Finally, having

defended three distinctive categories of analogy, the last section of the paper will

offer guidelines for recognizing the different types.

Figurative Analogies

Critical thinking is usually concerned with analyzing arguments by analogy, but

many important and useful analogies are not arguments. I Consider an analogy

offered by Samuel Johnson to illustrate the difference between argument and tes-

timony:

Argument is argument. You cannot help paying regard to their arguments, if

they are good. If it were testimony you might disregard it. ... Testimony is

like an arrow shot from a long bow; the force of it depends on the strength of

the hand that draws it. Argument is like an arrow from a cross-bow, which

has equal force though shot by a child. 2

Dr. Johnson effectively marks the difference between testimony and argument by

means of afigurative analogy. His analogy illustrates-and does not argue for-

that distinction. If you are not independently convinced that testimony depends

for its reliability on its source, while argument must stand or fall on its own merits,

then Johnson's analogy offers nothing to persuade you. That is not a flaw in the

analogy, unless one assumes that all analogies must be arguments.

Figurative analogies do not argue/ though they may elucidate. Experienced

physicians note that interns examining symptoms often forget the most likely diag-

nosis, favoring instead some exotic and improbable disease they have recently

studied. A popular parable describes a group of interns standing in the dark and

hearing hoofbeats, then concluding that it must be a zebra. The zebra analogy is

not an argument to prove that simpler diagnoses are often right; but it is a good

illustration of how neophyte physicians may be tempted to overcomplicate their

diagnoses, and a helpful reminder not to ignore the more mundane maladies.

Deductive Arguments by Analogy

Attempting to measure all analogies by the standards for good arguments means

ignoring figurative analogies, which require a different yardstick. But the oppo-

site mistake also occurs. The old saw that "analogies never prove anything"4

treats all analogies as ifthey were figurative analogies, ignoring the fact that many

analogies are arguments. When the distinction between figurative analogies and

arguments by analogy is recognized, there is still the danger of lumping distinct

types of analogical argument into one muddled category. Analogical arguments

divide into two basic types: deductive and inductive.

ClassifYing and Analyzing Analogies

201

Perhaps the most important type of analogy for critical thinking is the deduc-

tive argument by analogy. This is the use of analogy familiar in courts of law: Is

this new case really analogous to Jones v. Smith, or does it fit better with the

precedent established in Green v. White? Deductive analogies also figure promi-

nently in philosophical disputes: Think of Judith Jarvis Thomson's marvelous vio-

linist analogy in the abortion debate,5 Tom Regan's analogical argument for stop-

ping the use of animals in research,6 or John Searle's Chinese Room argument in

opposition to computer intelIigence. 7 These are compelling images, but they are

much more than that. In contrast to figurative analogies, they are powerful argu-

ments that aim to settle difficult issues. And they are deductive arguments by

analogy, not inductive. Inductive analogical arguments are important, but critical

thinking texts often treat all arguments by analogy as if they were inductive. De-

ductive analogies cannot be understood in terms ofinductive reliability, since there

is not a shred of induction about them.

Consider Judith Jarvis Thomson's famous violinist analogy. You awaken one

morning to discover that last night you were drugged, kidnapped, brought to a

hospital, and then connected to a distinguished but gravely ill violinist. The violin-

ist has suffered acute renal failure, and the toxins building in his bloodstream will

kill him ifhis blood is not purified. The Society of Music Lovers discovered that

you-and you alone-are the perfect blood match for the violinist, and so they

kidnapped you and hooked you up with the violinist, and now your kidneys are

doing double duty: purifying the blood of both you and the violinist. This process

will cause you no physical harm, though it is no doubt an inconvenience.

Everyone present (the kidnappers have done their dirty work and fled) agrees

that you have been badly wronged and your rights violated by the kidnappers. But

now if you unhook yourself, the violinist will die. Therefore-the hospital staff

inform you-you must remain attached to the violinist until a machine is built that

will cleanse the violinist's blood (construction will require about nine months).

Since unhooking yourself will result in the death ofthe violinist, if necessary they

will compel you to remain attached to the violinist. If you say-as most people

will-that such compulsion is wrong, then you must (on the basis of this deduc-

tive analogy) also conclude that it is wrong to compel a woman pregnant as a

result of rape to remain "hooked up" to the fetus. If you have a right to unhook

yourselffrom the violinist to whom you were involuntarily linked (even though the

violinist-person will die), then a woman who is pregnant as a result of rape has a

right to an abortion (even though the fetus-person will dieV

Deductive arguments by analogy have the following form:

I. We both agree with case a.

2. The most plausible reason for believing a is the acceptance of principle C.

3. C implies b (b is a case that fits under principle C).

4. Therefore, consistency requires the acceptance of b.

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Bruce N. Waller

Deductive arguments by analogy force us to think hard about the principles we

hold, and how they apply to other circumstances. Why do you believe you have a

right to unhook yourself from the violinist? If your answer is (the principle that)

we do not have an obligation to save or sustain a life when we have done nothing

to take on that obligation, then your own principle also implies that a woman who

is pregnant as a result ofrape does not have an obligation to save or sustain the life

of the fetus (has a right to an abortion).

One might dispute this argument in two ways: by disagreeing with the princi-

ple ("I believe I do have an enforceable obligation to stay hooked up to the violin-

ist"); or by claiming that the two cases don't fit under the same principle and thus

that the analogy is flawed ("The principle that justifies detaching myself from the

violinist doesn't apply to the woman pregnant as a result of rape"). But note two

things. First, this is certainly an argument. It claims that logical consistency

requires a specific conclusion. And second, it is a deductive (not inductive) argu-

ment. It does not suggest that since people generally believe they have a right to

unhook themselves from violinists, thus (inductively) they are also likely to hold

that rape victims have the right to unhook themselves from fetuses. (In fact,

Thomson may well believe that many people are inconsistent in their beliefs on this

issue, not having reflected on what their principles require; recall the slogan that

"if men could become pregnant, abortion would be a sacrament".) There is no

induction in Thomson's argument, but instead a deduction from principle.

Inductive Arguments by Analogy

Alice and Barbara are true soulmates, and in every area they have explored-

foods, sunsets, cars, architecture, poems, movies-they have similar tastes. Alice

may (perhaps correctly) conclude that she and Barbara are similar in all their

tastes; and she further concludes-on the basis of their similar tastes-that since

Alice likes Penelope Fitzgerald novels, Barbara wiII like them also. In that case,

Alice's inductive argument by analogy 9 would look something like this: We share

tastes in cars, foods, movies, and poems; such tastes are relevantly similar to

tastes in novels; so Barbara will also share my fondness for Penelope Fitzgerald

novels.

The structure of inductive analogical arguments can be represented as follows:

1. D has characteristics e, f, g, and h.

2. E also has characteristics e, f, g, and h.

3. D also has characteristic k.

4. Having characteristics e,f, g, and h is relevant to having characteristic k.1O

5. Therefore, E will probably also have characteristic k.

This is very different from a deductive argument by analogy, for there is no

implication that Barbara must like Fitzgerald novels in order to be consistent (the

claim made in a deductive argument by analogy). Suppose that Barbara surprises

ClassifYing and Analyzing Analogies

203

Alice, and hates the novel Alice recommended. Alice may be disappointed, per-

haps shocked; but Alice will not conclude that Barbara is being hypocritical, or

that she has some fundamental inconsistency in her belief set. After all, when she

recommends the novel to Barbara on the basis of their similar tastes, she is not

claiming that in order to be consistent-in order to follow some shared principle of

what constitutes an enjoyable novel-Barbara must like this novel.

Consider another example. Alice wants to save the whales, ban nukes, stop

acid rain, and promote civil rights: basic value commitments she shares with her

friend Barbara. So it is a reasonable inference-by inductive analogy-that since

Alice is a vegetarian, Barbara is also. If Barbara is a dedicated carnivore, that will

surprise Alice; but the inductive analogy does not imply that consistency compels

a vegetarian diet for Barbara. In contrast, when Alice offers Barbara a deductive

argument by analogy in favor of vegetarianism ("Look, you believe that it would

be wrong for smarter and stronger extraterrestrials to slaughter us for dietary

delicacies, right? So ...") then Alice is claiming that Barbara's failure to embrace

a vegetarian diet is a logical inconsistency, and not just an inductive surprise. To

see this from another angle, consider Barbara's response if she rejects Alice's

inductive argument, and affirms her taste for animal flesh: "How surprising! We

finally found a point in which our views do not match." Her rejection of the

principle behind a deductive argument by analogy will be quite different: "No, I

think you're wrong: if someone really is stronger and smarter, then they have

every right to use the weak and stupid for their dining pleasure."

Important differences are obscured if inductive analogies are analyzed under

the same pattern used f'Or deductive analogies. Framing the principle implied by a

deductive analogy is often difficult, but it may be possible to state it precisely and

fully; with inductive analogies, specifying the relevant similarities is a much tougher

task, requiring empirical research. In drawing an inductive analogy between a

horse's race last week and its upcoming race, it will be important to note that last

week the horse raced under "similar conditions" to those of today; but does that

imply exactly the same humidity, wind speed, lead ponies, and crowd noise? For-

mulating the principle behind a deductive argument by analogy also poses chal-

lenges, but the challenges are of a different sort than the challenges in determining

what is relevant to an inductive argument by analogy. In the former we are trying

to determine why we believe something (Why do we believe it wrong for extrater-

restrials to slaughter us? Why do I have a right to unhook myself from the violin-

ist?). That is not the sort of investigation required to determine what factors are

relevant to a runner's chances in the upcoming race. Determining relevance for

an inductive argument requires empirical knowledge of what factors are strongly

associated. (The author of the book is strongly relevant to whether Barbara is

likely to enjoy it; the color of the dust jacket is not-but that is a fact we learned

through experience, not deduction.) Furthermore, adding relevant characteristics

to the inductive analogy will strengthen the argument, while considering different

cases may help to narrow and specify the principle in a deductive argument by

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