critical thinking

“I don’t get why you want to quit,” said Malcolm. “You came here to play volleyball. Volleyball is all you ever want to talk about! Now suddenly you want to quit?”

Caitlin looked at Malcolm. He couldn’t possibly be this dense. “Look, I explained it all to you already.”

“You said that you didn’t like Coach Williams. So what? She’s your head coach. Nobody likes a head coach. I don’t like the marching band director, but you don’t see me quitting the band,” said Malcolm.

“Coach was screaming at everyone again. She’s so negative, always screaming at the players, and that doesn’t motivate me to try harder. I just hate all her yelling! Anyway, it’s the setter, Jenny; she kept putting the ball too far from the net. It messes up everybody. But coach kept yelling at the rest of us, when it was all Jenny’s fault.”

“So,” said Malcolm, “you’re quitting because the coach yells at you? Williams has been a screamer since she took over as head coach two seasons ago. Her yelling never bothered you before. Or is it something else?”

“Yes! No. I don’t know,” replied Caitlin in exaspera- tion. “Who cares? It’s not like I have a future in volleyball after college.”

“What does that have to do with anything? You knew a spot on the Olympic team or the AVP beach volleyball pro tour was like a near-impossible long shot before you came here. And another thing: Don’t tell me you don’t get moti- vated when the coach is fired up. I’ve seen you in games. You’re angry because you know you can play Jenny’s posi- tion better than she can. But the coach doesn’t let you. So, you’re pissed at the coach. It’s not about the yelling.”

“You’re right. Jenny’s terrible. I don’t understand how she ever made the team.”

“But, Caitlin, nobody can spike and defend at the net like you. Coach knows that, and so does everyone else on the team. So, you’re going to play the front line. Which is great. I’ll bet that Jenny wishes she could play where you play.”

“Well, I don’t care about any of that anymore. I’m quitting and therefore I’m quitting. End of story. Let’s talk about something else. . . . Tell me how your marching band practice was today.”

“Fine, I hear you. You’re going to quit. And, yes, we can change the subject. But let me just say for the record that I still don’t think you’re really being honest about why you’re leaving the team and the sport you love. And just saying over and over again that you plan to quit does not explain why you plan to quit.”

In the scene that just played out, Caitlin explains her decision to quit the college volleyball team. Her stated reason is that she is not motivated to play harder by the coach’s constant criticism. Ergo, she’s going to quit the team. That may be a reasonably logical argument, if we also assume that Caitlin is the kind of athlete who does

not respond well to that coaching style. But her friend Malcolm knows better. He does not accept her argument because he has seen her respond positively to the coach’s style in game situations. The truth is that Caitlin does get motivated to play harder when the coach is fired up. Although Malcolm does not make the point, we might observe that the word yelling is negatively slanted. It fits Caitlin’s current negative attitude toward the coach. But “yelling” is probably not the best word to use when talk- ing about those times when the coach is successful in motivating Caitlin.

Caitlin offers another argument, saying that she has no future in volleyball. Malcolm points out the irrelevance of that consideration, and then he suggests that her real rea- son for being upset with her coach has to do with which position she wants to play. Caitlin ends the conversation about volleyball with a definitive and somewhat defensive, “I’m quitting and so I’m quitting.” Malcolm makes it clear that her final statement forcefully affirms her intention, but it is not an acceptable answer to the question “Why?”

Throughout their conversation Malcolm has been evaluating his friend Caitlin’s arguments. This chapter focuses on building argument evaluation skills. It presents a comprehensive and straightforward evaluative process that we can apply in everyday situations, much in the way that Malcolm did in the opening conversation with Caitlin. The process includes four specific tests. An argument must pass all four tests to be considered worthy of acceptance as proof that its conclusion is true or very probably true. Each of these four criteria is rooted in the natural and universal human practice of making arguments and giving reasons. Because critical thinking requires skill at evaluating argu- ments in real-life contexts, we begin with the expectations and responsibilities associated with giving reasons and making arguments.

7.1 Giving Reasons and Making Arguments

The dynamic conversational practice of explaining to one another the reasons for our claims—that is of making arguments—is part of every human civilization and cul- ture. Every natural human language includes terminol- ogy and social conventions for making arguments as well as for evaluating them. But argument making is sensible only because of a set of presumptions we all implicitly rely upon to engage in this practice successfully. These presumptions are operative wherever and whenever peo- ple engage in a sincere effort to make arguments to one another regarding a decision about something of serious mutual concern. These presumptions form the basis for the expectations the listener has—and the responsibilities

the argument maker has—when offering reasons to explain why the argument’s claim is worthy of acceptance as true or very probably true.

Truthfulness

The practice of argument making rests in part on the presumption upon which so much of human discourse depends, namely that the speaker is telling the truth. In other words, when making arguments we expect that the statements offered as part of any reason are, in fact, true. As a rule, people collaborating with one another to think something through do not intentionally use erroneous information or lie to one another. If a disagreement about the truth of any statement that is part of a reason should arise, then the people involved have two options. They can make an effort to find out if that statement is true, or they can qualify the force with which they assert and maintain any claims in the line of reasoning that relies on that state- ment. Of course, people do lie on occasion. And so this presumption often goes unfulfilled.

In Chapter 5 we used the familiar term premise to refer to a statement, either explicit or implicit, that is a compo- nent of a reason. Another way to express the truthfulness presumption is like this: In a conversation that involves making arguments, we expect that all the premises offered are in fact true.1

The assumption that premises are true provides a reasonable basis for moving to consider whether those premises imply that the conclusion is true or very prob- ably true. But without first really considering the truth- fulness of the premises, it becomes only a conceptual exercise, rather than a matter of practical significance, to consider the argument’s logical strength. Here are two arguments with true premises.

• Chicago is north of St. Louis. St. Louis is north of New Orleans. Therefore, Chicago is north of New Orleans.

• There are 325 children registered in grades 1 through 6 at the Carver Elementary School. We have tested 40 percent of these children for reading skills. We also have taken a number of physiological measurements of each of those same children. Our data show that there is a strong positive statistical correlation be- tween the size of a child’s feet and the child’s reading skill level.

Not sure if the premises in the first example are true? No problem. We can check a map or pull up Google Earth and find the relative position of the three cities mentioned. Regarding the second example, one obvious question is whether the measurements mentioned in the third sentence included foot size. If not, we may want to call into question the truthfulness of what the speaker is saying. If the speaker does not have any information about the children’s foot sizes, then the speaker’s argu- ment falls apart.

Logical Strength

Consider the following example. In this case, were we to take the premises to be true, then its conclusion would have to be taken as true as well.

• We have been keeping track of how often the weekday 6:56 am Caltrain from San Francisco arrives late at the Millbrae station. We conducted three 6-week surveys over the past 12 months. In each survey the week- day train arrived at the Millbrae station late 24 out of 30 times. Therefore, there is an 80 percent probability that the weekday 6:56 am Caltrain will arrive late at the Millbrae station.

In this next example let’s assume that what the speaker is saying about John is true and let’s assume that we agree with the speaker about the pattern of behavior that is the precursor to a breakup. If so, then it seems reasonable to conclude that the relationship with John will not endure. • This is not the first time someone has broken up with me. I recognize the pattern. First the person is too busy to do things together. Then the person doesn’t return texts or phone calls. Then the person “forgets” that we had plans. And then comes the “we can still be friends” conversation. John has progressed to the “too busy” phase. As much as I don’t want to believe it, my rela- tionship with John is probably heading for a break up.

Assume, for this next example, that there was a comet one night and that the next day the king took ill. So the premises are true. But the reasoning is an unacceptable leap from those observations to a claimed causal relation- ship. The premises of this argument do not logically justify accepting conclusion as true.

• I saw a strange light streak across the midnight sky last night. And, look, this morning the king became deathly ill. This can only mean that the strange light in the night sky caused our king’s sickness.

When someone offers an argument, the speaker’s reason is supposed to be the logical basis for the speak- er’s claim. The point of giving reasons for our claims is that the reasons support the claims. The second

presupposition of the practice of argument making is that the speaker’s reason, if true, is the logical basis for the speaker’s claim. Notice that this is hypotheti- cal. Were we to assume that the reason a person gives for his or her claim is true, that assumption would then imply that the person’s claim is probably or necessarily true as well. In the language of logic, this presupposition is expressed this way: The assumed truth of the premises of an argument justifies or implies that the conclusion of the argument also be taken as true.

Most people would sooner die than think; in fact, they do so.

Bertrand Russell, Author, Mathematician, & Philosopher2

Relevance

It happens that a conclusion might be true independent of whether the premises are true or whether the premises logically support the conclusion; because this is so, when we make arguments we also presume that the truth of the reason is relevant to the claim. This presumption might be called the “So What?” presumption. Consider this

example, where the premises are true and the conclusion is true, but the reason is not relevant to the claim.

• To many around the world, the Statue of Liberty sym- bolizes the welcome our nation extends to all freedom- loving people. So, as the great Yogi Berra says, “You can observe a lot just by watching.”

This argument is so odd that it would get a squawk out of the Aflac duck. The reason given has no relevance to the truth of the claim. Their only connection is that Yogi Berra happened to have been a player for the New York Yankees, and the Statue of Liberty happens to be in New York. That happenstance is not sufficient to say that the one is relevant to the other. If anyone were to seriously present this rea- son as the basis for the truth of the conclusion we would say, “So what? That’s not relevant!” And this reveals our third presupposition: the listener takes the reason given by the speaker to be relevant in believing the speaker’s claim.

There is no point to giving reasons if the listener is not going to rely on those reasons in deciding what to believe with regard to the claim. Recall that in our opening example, Caitlin changed her story about why she wanted to quit the volleyball team. At first she talked about how the coach’s yelling and berating players was her issue. But then she gave a different reason, saying that she was going to quit because she did not anticipate a future as a professional volleyball player. Malcolm challenged her on that, noting that it was not even relevant, in his view. A future in professional volleyball was never her reason for joining the college team, and the absence of that opportu- nity is not relevant to why Caitlin now wants to quit the team. Everyone, including Caitlin, may believe that Caitlin wants to quit the volleyball team. But nobody, not even Caitlin, believes that whether or not she has a future in professional volleyball has anything to do with her want- ing to quit at this point in time.

Non-Circularity

Our fourth precondition when we give reasons for our claims is that the claim must not be part of the basis for believ- ing in the truth of the reason. Argument making in real life is essentially a one-way street: The reasons are used to

because in mapping arguments we used the arrow con- vention to display the intended directionality of the argu- ment maker’s reasoning.

In the Dilbert’s cartoon strip the boss criticizes Dilbert’s presentation for being full of technical words and way too long. We naturally think that the boss came to those conclusions about the presentation by having seen it and evaluated it. But no. The boss then turns around and uses those same two claims as his reasons for not seeing or evaluating the presentation. It makes no sense to give a reason as the basis for one’s claim and then to use that claim as the basis for one’s reason. In a comic strip, circular reasoning is funny, and in real life it can be infuriating.

7.2 The Four Tests for Evaluating Arguments

The four presumptions about argument making as an interpersonal human activity form the bases for the four evaluative criteria applicable to all arguments. In other words, it would be reasonable to accept a person’s argu- ment if it met all four of the conditions implied by those presumptions. Given a reason offered in support of a claim, these are the four conditions that must be met:

1. To the best of our knowledge and understanding, the reason is true.

2. The logical relationship between the reason and claim is such that the reason implies, entails, strongly warrants or strongly supports the claim, such that the claim must be true or very probably true if the reason is as- sumed to be true.

3. The relevance of the reason to the claim is such that the truth of the claim actually depends on the truth of the reason.

4. The flow of the reasoning is such that truth of reason must not depend on the truth of the claim.

An argument that satisfies all four conditions is wor- thy of our acceptance as a proof that its claim is true or very probably true. We will apply the adjectives good and

worthy to those arguments. A good argument or a worthy argument is an argument that merits being accepted as a proof that its conclusion is true or very probably true. The four conditions listed to define four tests to apply when evaluating arguments are to be applied in the order given. As soon as an argument fails to meet one of the four, it is no longer eligible to be considered a good or worthy argument. Let’s see how to apply each of these four to determine whether or not an argument is worthy of acceptance.

Test #1: Truthfulness of the Premises

In everyday situations, the truth or falsity of premises is our first concern. If one or more of the premises of an argu- ment is not true, then, for all practical purposes, there is little point in moving forward to evaluate other aspects of the argument. Our first job is to get our information straight. The critical thinking habits of truth-seeking and inquisitiveness demand that we cou-

rageously endeavor to learn what we can before mov- ing forward with claims and arguments based on incomplete knowledge.

The Test of the Truth- fulness of the Premises is a favorite in police dra- mas. We have all seen the scene in which detectives interrogate someone who gives a lame alibi like this one: “My friends and I were at a movie the night the crime took place.” The detectives check the story and discover it is a lie. Having

A person who has never been drunk cannot be an alcoholic.

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exposed his lack of truthfulness, the detectives no longer accept the person’s alibi and may even make the liar their prime suspect.

Test #2: Logical Strength

One practical way to apply the Test for Logical Strength is to challenge yourself to imagine a situation, if possible, in which all the premises of an argument are true, but the con- clusion is false. If there is no possible scenario in which all the premises of an argument can be true while at the same time its conclusion is false, or if such a scenario is extremely improbable, then the argument passes the Test of Logical Strength.3 However, to the extent that such a scenario is possible, plausible, likely, or actually true, the argument fails this test.4 If there is a possible scenario, but it is remote and implausible, perhaps as unlikely as 1 chance in 20 or 1 chance in a 1,000, then we can maintain a comparable degree of confidence in the argument’s logical strength. Logicians call an argument with true premises that has also passed the Test of Logical Strength a sound argument.5 Sound is used here in the sense of “healthy,” meaning that such an argument ordinarily is rather robust and deserves our attention as we deliberate what to do or what to believe.

What if there is more than one independent reason given to support a claim? Does discovering that one reason has a false premise make the claim unacceptable? Consider this example; here a claim is supported by two reasons, which the speaker wants the listener to take as indepen- dent considerations.

• “I’m not an alcoholic. First of all, I only drink beer. And, second, I’ve never been drunk in my life.”

Map #1 shows the two reasons as independently sup- porting the claim.

Suppose we discover that the speaker is telling the truth when he says that he only drinks beer. However, the implicit but unspoken premise (“Someone who only drinks beer

cannot be an alcoholic”) is false. So, the first argument fails the Test of the Truthfulness of the Premises. Suppose we then discover that the speaker is also being truthful when he says that he has never been drunk in his life. This, along with the generally accepted truth of the implicit, but unspoken, prem- ise “A person who has never been drunk cannot be an alco- holic,” indicates that his second argument passes the Test of Truthfulness of the Premises.

The Test of Logical Strength comes next, and the sec- ond argument also passes that test. It is difficult to imag- ine a case where a person who has never been drunk is an alcoholic, although it is not impossible to imagine such a case. So, it would seem reasonable to accept that our speaker is not an alcoholic, even though one of his reasons (that he only drinks beer) was poor. His second argument, based on the other reason (he has never been drunk in his life), which is independent of the first, was sound.

People often provide multiple independent reasons for a given claim and some of those reasons may turn out to be false. One may be inclined to dismiss the claim itself, having heard the speaker present one unsound argument.

Dismissing an otherwise-worthy claim simply because one or more of the arguments made on its behalf contains false reasons is one of the most common human reasoning errors. Before determining that a claim should be rejected, a strong critical thinker would first need to find problems with the soundness of all the arguments being advanced.

Because there are so many important varieties of argu- ments, which require special attention when testing for logi- cal strength, we will suspend this discussion at this point but return to it again in the coming chapters. We will devote Chapters 8 and 9 to the evaluation of inferences. And then later we will look more closely at inferences based on pat- tern recognition, ideological reasoning, and empirical rea- soning. For the moment, let’s complete our review of the four basic tests of an argument’s worthiness to be accepted.

Test #3: Relevance

The Test of Relevance requires making a reasoned judg- ment that the truth of the conclusion depends upon the truth of the reason given. If an argument passes the first twotests, then The Test of Relevance is the next one to apply. Recall that the presumption we are seeking to fulfill is that the author’s reason is, in fact, the basis for believing the claim. And the listener must judge if accepting the claim as true depends on support derived from that reason. For example, the following example passes the Test of Relevance.

• A study from the Harvard Center of Risk Analysis estimates that cell phone use while driving contributes to 6 percent of crashes, which equates to 636,000 crashes, 330,000 injuries, 12,000 serious injuries, and 2,600 deaths each year. The study also put the annual financial toll of cell phone– related crashes at $43 billion. The research investigated whether or not a hands-free device was less dangerous. The statistical evidence suggests not. It appears from the data that the fact that the driver was distracted by the conversation was a greater factor than was the type of cell phone technology, hands-free or not, that was being used. The researchers concluded that using cell phone technol- ogy of any kind while driving was associated with a greater risk of automobile accidents.6

By contrast, the next argument fails the Test of Relevance.

Is it reasonable or ethical for another driver to expose you to greater risk just so he or she can text a friend?

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So, how does a person connect San Francisco’s Golden Gate Park with a trip to the Botoli Garden in Florence, Italy? Find out about the influence that unreflective associational thinking has on human decision making in Chapter 10.

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• Yeah, I’m looking forward to visiting Italy, you know, Old Europe. Why is too obvious. See, I’ve been work- ing part-time at the Golden Gate Park in San Francisco. It’s incredible there. Beautiful, open, free. There’s this one garden there that kind of reminds me of pictures I’ve seen of Italy. I love being outside in the spring, the flowers and the fresh air, the smell of fresh-cut grass. And all that makes me think how great it would be to just live slow and relaxed, like they do in Europe, tak- ing life as it comes. You know what I mean?

That the research on car accidents and cell phone usage is relevant to the conclusion in the first example is obvious in the first example. The connection between visit- ing Italy and working part-time in Golden Gate Park in the second example seems to be tenuous at best, more based on the person’s free association of ideas than on any actual evidence. Even if the speaker imagines a connection, the listener can judge that the reason given, even if true, is not a basis for believing that the speaker wants to visit Italy. In fact, if the speaker had simply said, “I want to visit Italy,” that might have been more credible than his having come up with the far-fetched and irrelevant dissertation about the glories of a part-time job in a city park—even if it is one of the greatest public parks in this nation.

Applying the Test of Relevance is substantially easier for people with knowledge and experience appropriate to the context and issues under discussion. For example, U.S. laws prohibiting using gender as the basis for workplace promotions express American society’s judgment that a per- son’s gender is not a relevant consideration when deciding whether the person merits a promotion. In another country with a different set of cultural mores, gender-based promo- tion decisions might be considered both legal and reason- able. The Test of Relevance is important because people often make the argument that they should be excused from

responsibility for certain actions. However, as a people, having heard these arguments before, we have come to the judgment that certain reasons are not going to be accepted as relevant. For example:

• Claiming that one was following the direct orders of one’s superior is not a relevant defense against charges of war crimes.

• Claiming that one’s judgment was impaired by drugs or alcohol is not a relevant defense against charges of vehicular manslaughter resulting from driving while under the influence.

• Claiming that one must protect his or her GPA because one plans to become a doctor is not a relevant defense against charges of academic dishonesty in any course, including general education elective courses.

Test #4: Non-Circularity

The fourth and final test of an argument’s acceptability is the Test of Non-Circularity. This test requires that a claim is not being relied upon either implicitly or explicitly as part of a chain of reasoning used to support its own rea- son. If such a chain looping back on itself is found, then the argument maker is reasoning in a circle. An argument is like a river that flows in one direction, from reasons and

evidence toward the conclusion. A river cannot feed itself and still be described as a river; rather, it becomes a stag- nant moat. So it is with good arguments: Claims cannot be the bases for their own reasons. If they were, then the rea- soning would simply be stagnant and self-justifying in the most unflattering sense.

The final argument Caitlin made about quitting the volleyball team was “I’m quitting and therefore I’m quit- ting.” Here the circle is so tight that the reason and the

claim are identical. The map of her circular argument would look something like Map 2.

We can interpret this way of speaking as a way of emphasizing one’s claim, but not as a way of proving one’s claim. It is like saying “I’m quitting” real loud. But volume is not proof.

Reasoning in a circle results most frequently from the use of multiple arguments in combination with each other. At times people lose track of the reasons for their beliefs, forgetting, for example, that their basis for believ- ing one idea, X, was because they accepted another idea, Y, and that their reason for accepting Y had been their belief in X. The result is that the person has high con- fidence, although misplaced, in both ideas. However, because their support for X is Y and their support for Y is X, the reasonable thing would be to have no confidence in either. For example, consider the pair of arguments in this passage:

• I’m sure we can make this marriage work. That’s why we’re talking through our problems, which shows that we still care for each other. And that’s why I’m sure we can make this marriage work.

The speaker’s reason for the claim that the marriage is salvageable is the belief that both parties still care for each other. And the basis for believing that goes back to the idea that the marriage can be saved. If we were to map

these arguments, it would look like Map 3. This reasoning is as fragile as a house of cards; touch it in the least with an analytical finger and it collapses upon itself.

Argument Making Contexts

There is nothing about argument making that demands that the format be a debate. There is nothing about argument making that requires that it be an adver- sarial confrontation either. In fact, it does a great dis- service to decision making and collaborative effort to imagine the process must be oppositional or confronta- tional. In an adversarial context, it is too easy to forgo truth-seeking in the false belief that argument making is simply the search for facts that support one’s preconcep- tions. Too often, the courageous desire for best knowl- edge is trumped by the competitive need to vanquish the opposition. In that case, the honest pursuit of reasons and evidence, wherever they may lead, even if the rea- sons and evidence go against one’s preconceptions or interests, is abandoned because intellectual honesty and integrity are not always suitable virtues for warriors who must bring home the victory for their side. Just like win- ning a legal action does not guarantee that justice has been done, winning an argument does not guarantee that we have made the best decision or that we have dis- covered the truth. Taking a page from the best practices of scientists and criminal investigators, optimal decision

making and problem solving are more likely to occur when we are fully invested, focused, and yet objective about our argument making.

Good arguments—subtle and yet effective as solid proofs that their claims are worthy of being accepted as true—can be expressed in so many ways that listing them all may be impossible. In natural language contexts argument making can take the form of a personable and convivial conversation between friends as they explore options and consider ideas. Good argument making can occur in front of juries and judges in the push and pull of a legal dispute. Managers seeking budget approvals present arguments for more funding. Fundraisers seek- ing donations offer reasons that tug at our minds and our hearts for why we should contribute to their chari- ties. Researchers present complex and detailed argu- ments when reporting their findings in professional journals. Good argument making can be embedded in warnings, ironic commentary, allegorical dramas, one- line counterexamples, recommendations, policy state- ment preambles, public addresses, conversations, group meetings, negotiations, comic monologues, serious pro- and-con debates, meandering reflections, and even the lyrics of songs.7

The vocabulary we use to evaluate arguments must be as flexible as our understanding of the wide variety of contexts within which argument making can be found. A conversation with a colleague about an impending deci- sion can be helpful, even if we would not think about calling it valid, or persuasive. Natural language offers such richness in its evaluative repertoire that it seems wise, at least at this early point, not to close our options by prematurely stipulating a set of evaluative categories. Thus, with the understanding that the terms listed in the table “Evaluative Adjectives for Arguments and Their Elements” are not meant to be interpreted rigidly or in some special technical way, let us simply go forward with our evaluation of arguments using common language. The table offers suggestions regarding the range of evaluative adjectives that might reasonably be applied when evaluat- ing the different elements of major concern, data, warrants, claims, and arguments.

7.3 Common Reasoning Errors

Humans learn from their mistakes. We can capitalize on that truism to strengthen our skill in evaluating arguments by studying those errors of reasoning that have over the centuries earned themselves a reputation as alluringly deceptive and misleading. As a group they are called “fal- lacies.” Fallacies are deceptive arguments that appear logi- cal and seem at times to be persuasive, but, upon closer analysis, fail to demonstrate their conclusions. Many types of fallacies have their own name, as we shall see.

Learning to recognize common fallacies and learning how to explain in ordinary, non-technical terms the mis- taken reasoning they contain is a great aid to evaluating arguments. The seven fallacies of relevance described in this chapter are types of arguments that will fail the Test of Relevance. In Chapters 8 and 9, to help with the appli- cation of the Test of Logical Strength, we will expand the list of fallacies to include several more.8 Skill in recogniz- ing when someone is making a fallacious argument is a strong defense against being misled about what to believe or what to do.

Fallacies of Relevance

Like alerts warning of bad weather, for centuries logi- cians have supplied lists of the kinds of deceptive argu- ments that tend to mislead people.9 When it comes to being deceived by the rhetoric of gifted speakers, elo- quent writers, or clever advertisements, many of us are no wiser or more sophisticated than people were in Aristotle’s time. Yet in our effort to make an honest argument to another person about what to believe or what to do, we are asking that person to accept the truth of the claim because of the reason given. This expectation of relevance at times goes unfilled. Instead we provide a reason that is not relevant. Creative questioning is a powerful tool for uncovering the false assumptions that lie at the core of fallacies of relevance. Whatever the spe- cific application of the question, the fundamental issue is “What does that reason actually have to do with thatclaim?” From this fundamental concern we can derive a number of more specific queries.

It is impossible to list all the ways that the reason given might be irrelevant to the claim being made. There are too many ways to be irrelevant. Some arguments appeal to tra- dition, others, particularly in marketing, try to sell us some- thing simply because it is new. Some use emotions such as fear to move us to accept the claim being made. Others try flattery, praise, trust, or affection to move us to accept a claim that we otherwise would not believe. Some challenge our ability to quickly come up with an alternative. Or they toss in an irrelevant cliché. Others barrage us with true but irrelevant statements anticipating we will accept the conclu- sion sooner or later out of sheer mental fatigue.

• Nice idea, but it’s not for us. We don’t change horses in midstream.

• Try the mushroom, jalapeño, mango margarita. It’s new!

• It would be a grave mistake to think that there is no Hell. In fact, an eternal error.

• Hey, trust me. Would I lie to you, baby?

• Absolutely she was the one who told that lie about you. Who else would have done that?

Many kinds of irrelevant appeal fallacies are so notori- ous that they have earned their own name. The name can be helpful to remembering the type of mistaken assump- tion being made.

appeals to Ignorance It is false to assume that the mere absence of a reason for (or against) an idea should itself count as a reason against (or for) the idea. Consider these examples:

• We know we have a corporate spy someplace in the organization, probably on the management team itself. There is no evidence that it is Francesca. In fact, she’s too clean, if you know what I mean. We should fire Francesca; she’s got to be the spy.

• Someone here took my computer and I need it back. Who was it, John? Was it you? No, you say. Well prove it! Aha, you have no proof to offer. Well then, John, it was you. And I want it back now!

• Impressionism, and especially French Impressionism, is the best form of art. You don’t believe me? Then name some other form that has been proven to be more beautiful. You can’t, can you? So, I’m right.

appeals to the Mob It is false to assume that because a large group of people believes something or does some- thing that their opinion or their behavior is necessarily cor- rect or appropriate. Here are two examples of the Fallacy of Appeal to the Mob, also known as the Bandwagon Fallacy. This seems like such an obvious mistake that it may be hard to imagine that people can be so gullible as to think

If you cannot name a superior art form, does that imply that French Impressionism is the best art form?

something is true just because everyone believes it. That is, right up until you remember the power that mythology and superstition still have in this world.

• Everyone knows that a black quarterback will not be able to lead an all-white team. So we will not put Doug Williams at the quarterback position.10

• All the kids at school are getting tattoos. Every one of my friends has one, and some have two. I see adult men and women with tattoos. So, I’m thinking that it’s about time that I get a tattoo.

• A lot of people like Michigan State to win the Big 10 Championship this year. So I guess I’ve got to go with the Spartans as my pick too.

• Everyone believes Martha might be practicing witch- craft, so be careful how you act when she’s around.

appeals to eMotIon It is false to assume that our initial emotional response to an idea, event, story, person, image, or proposal is necessarily the best guide for form- ing reflective fair-minded judgments. Chapter 10 discusses this in greater detail, because the relationship between our emotional responses and our decisions about what to believe and what to do are complex. Because gut reaction and reasoned reflection are both real factors in human deci- sion making, strong critical thinkers learn to draw on both of those resources. But, at times, people offer fallacious argu- ments that provide nothing more by way of a reason than

an appeal to one’s unreflective emotional response. Here are some examples of the Appeal to Emotion fallacy, which tends to rely on emotionally loaded words and expressions.

• I love you like the son I never had, and so I believe you. No, I must believe you. Love leaves no other option.

• He’s a lousy, rotten terrorist. One of those people. So, there’s no question but that he deserves to die.

• Watch out—the political right is populated by a dan- gerous pack of hate-mongering jackals. They will destroy this nation because they have no respect for the truth or common decency. You can’t believe any- thing they say.

• Watch out—the political left is a goose-stepping gag- gle of dangerous tax-and-spend activists. They will destroy this nation with their bloated, ineffective social programs that we hardworking taxpayers can’t afford. You can’t believe anything they say.

• I know you have your heart set on going to Stanford; it’s something you talked about since you were in the ninth grade. You kept up your grades, aced the SATs and did everything you could to be admitted. And, I’m so proud of you, you did it. Everyone is. And you know what, I don’t care what it takes or what the fam- ily has to do, we’ll mortgage the house, get another

job, anything. But somehow, some way, whatever it takes and whatever the consequences for me or for your younger brothers and sisters, we are going to find the money so you can go to Stanford. I’ve made up my mind. That’s what we’ll do!

ad hoMIneM attacks It is false to assume that because the person making the argument is deficient in some real or imagined way, the person’s argument, work product, or views should not be accepted on their own merits. Ad hominem is Latin for “against the person” and it expresses the error this fallacy makes, which is to claim that a person’s ideas must be tainted because the person has some vice or flaw. The opposite would be equally falla- cious, which is to assume that because the person making the argument is virtuous the argument must be good, too. Strong critical thinking no more obliges us to reject every argument a convicted felon makes than to accept every argument the Dalai Lama might make. Arguments are to be judged on their own merits, not on the merits of their pro- ducers. The Ad hominem fallacy is a favorite verbal assault weapon in the arsenal of talk-radio hosts.

•

I don’t trust you because of what you did last week at the party. Don’t bother trying to explain yourself. As far as I’m concerned, anything you say is a lie. The guy’s a lazy, rich moron, and an egomaniac. He’ll never be elected. So why are you bothering to try to understand his proposals on tax reform and immigra- tion? They have to be total garbage.

• I’ll grant you that President’s nominee is a widely respected Harvard educated physician. And that he is known for his many years of working to improve medical services for the poor. But a few years ago he once tweeted that hand guns were an urban health hazard. So as far as I’m concerned, that comment alone shows he is not qualified to be Surgeon General.

• The Senator was spotted drunk in a Bangkok bordello. There are pictures on the Web already. So we can’t believe anything he says about environmental prob- lems or clean energy solutions.

• You have nothing of value to contribute to this conver- sation about minority race relations. You’re not black, Latino, Asian, Native American, or anything. You’re white.

• I’m sorry, but I don’t find his income and expense pro- jections credible. I don’t see how he could have done those numbers correctly. After all, we know he’s look- ing for another job. He has no company loyalty.

straW Man Fallacy This fallacy relies on the false assumption that, by refuting a weaker argument among several independent reasons given in support of a claim, one has successfully refuted all the reasons for that claim. For example:

• Look, we can’t approve your request for additional advertising funds. You said that one of the four mar- keting options you were reviewing was Web page design. But we have a policy not to support any fur- ther Web-based development.

• You said that legalizing pot was a good idea, because then pot could be regulated for quality and taxed. And you said it would permit us to shift law enforce- ment resources toward preventing other more harm- ful criminal behaviors. But I’m opposed to new taxes of any kind. So, I cannot agree with you about legal- izing pot.

A variation on the theme, also called the Straw Man Fallacy, is the pernicious practice of attributing to the opposition an argument that is not theirs, and then demolishing that argument. The misattribution may be mistaken, or worse, intentional. From this the per- son committing the fallacy misleadingly then argues that he or she has destroyed the opposition’s position entirely. Besides being intellectually dishonest and incon- sistent with the critical thinking virtue of truth-seek- ing, this practice violates the values of objectivity and fair-mindedness.

Adopting the strategy of trying to make an idiot out of your opposition can be risky. To use straw men and mis- representations when presenting the opposition’s argu- ments can lead one’s listeners, and at times one’s self, to the

mistaken belief that there is little or no merit to the opposi- tion’s view. In the vicious health care reform debates dur- ing the summer of 2009, those opposed to “death panels” demonized the proposed legislation for a provision that, as it turned out, was already part of existing Medicare law. The actual provision to which they objected provided for reimbursement to health care providers if patients volun- tarily sought end-of-life counseling about such matters as living wills, power of attorney, do not resuscitate (DNR) orders, or hospice care. When the dust settled, even some who had raised the specter of government death panels backed away from that overly dramatic straw man criti- cism. Others, however, continued to believe wrongly that the proposed legislation would mandate euthanasia.

Underestimating one’s opponent in a debate or dis- pute can backfire. One reason is that listeners can be alienated when they realize that we have not been fair or objective. A second reason is that we may become overconfident. Strong critical thinkers try not to mislead themselves. They school themselves to follow the politi- cal adage, “Never believe your own press releases.” In so doing, strong critical thinkers try not to confuse defeating

a straw man argument with giving due consideration to the opposition’s array of worthy arguments.

playIng WIth Words Fallacy Vagueness and ambiguity can be problematic in certain contexts. The Playing with Words Fallacy exploits problematic vague- ness, problematic ambiguity, donkey cart expressions, stereotyping, and slanted language in attempting to sup- port a claim. Because Playing with Words Fallacies are so varied and so vexing, we devoted Chapter 4 to learning how to apply our critical thinking skills to resolve those problems. Here are three more quick examples of argu- ments that are fallacious because they exploit problematic uses of key terminology.

• •

Everyone who is in prison can still be free, for true freedom is the knowledge of one’s situation. The more one knows about one’s self, the more one is truly free.

I’m selfish, you’re selfish. When you really look at it, everybody tries to meet their own needs. So, we are wrong to be so harsh on a guy just because he spends all his money on nice clothes and fine food for

himself while letting his children run around hungry and in rags.

• We cannot know that others experience the world as we do. To truly know is to be inside the minds of oth- ers. And that is simply not possible.

MIsuse oF authorIty Fallacy One version of the Misuse of Authority Fallacy relies on the false assump- tion that if a powerful or popular person makes a claim, then the claim must be true. In addition to this error, there are other ways that expertise can be misrepresented and misused. We talked about the many characteristics of an authority whose word should, in all probability, be accepted. Because reliance on the word of another is such an important part of how people decide what to do or what to believe, critical thinkers are alert to the falla- cies of Misuse of Authority. Here are a couple more quick examples:

• When asked why the curriculum had been changed, the Superintendent of Schools replied that the city’s Chamber of Commerce had advised that the stu- dents in the Junior High School would be education- ally better served if all teachers used more class time to prepare students to take standardized math tests and less time on American History, Creative Writing, Social Studies, Art, Leisure Reading, or Health Education.11

• In the annual NCAA March Madness office pool, the boss picked North Carolina State to win it all. I’m go- ing to pick the same team she picked. After all, she’s the boss.

The written historical record shows that the ques- tion of how to evaluate arguments goes back at least 2,500 years to the birth of the field study today known as logic. Logic, with its historical roots in rhetoric and argumenta- tion, explores the question of how to decide whether or not the claims based on various kinds of arguments should be accepted. More specifically, it focuses on one of the four presumptions of the practice of argument making: If the premises of an argument are taken to be true, that implies that the argument’s conclusion is probably or necessarily true as well.12

The wisdom and intellectual treasures of many of the world’s great cultures and civilizations are evident in the rich history of logic. Fortunately, there are many impor- tant and enduring lessons that critical thinking can draw from the study of logic with regard to testing the logi- cal strength of different kinds of arguments, recognizing common fallacies, and understanding the conditions for using various methods of reasoning correctly. Drawing on those enduring lessons, we have begun to assemble our tool kit for evaluating arguments in this chapter. Later, we will add some precision tools for the evaluation of arguments.

JOURNAL

Summing up this chapter,

the universal human practice of reasoning with a friend or colleague to seek the truth reveals how, in argument making and reason giving, four important presump- tions support the expectations and responsibilities that make that practice work in real life. The reasons we give should be true. The arguments we use should be logical. The reason given should be a relevant basis for accepting the truth of the conclusion. And the conclu- sion should not be used to lend support or credence to the reason. These four conditions ground the applica- tion of four straightforward tests to determine whether

Key Concepts

good argument/worthy argument is an argument that merits being accepted as a proof that its conclusion is true or very probably true.

sound argument is an argument with true premises that also passes the Test of Logical Strength.

Applications

Reflective Log

the ethics of fallacious argumentation: What if we dis- covered that we could manipulate the voting public more effectively by the use of fallacious arguments than by the use of worthy arguments? Consider the political impact of the “death panels” issue described under the Straw Man Fallacy. The entire episode generated more heat than light. And, yet, it may have achieved its political pur- pose. Many who heard and believed that the proposed legislation envisioned a eugenics program akin to that advanced by Nazi Germany showed up at town meetings to vent their anger and voice their objections. If the goal was to delay or derail the Democratic legislative agenda,

Individual Exercises

evaluate argument worthiness and explain—tests 2, 3, and 4: Assume that all the premises that are asserted are true. Apply the remaining three tests to evaluate each argument to see if it is worthy of acceptance. Remember, if the argument fails a test, you do not have to apply any fur- ther tests because at that point the argument is not worthy to be accepted. In each case, give a detailed explanation to

an argument is worthy of being accepted. The four are the Test of Truthfulness, the Test of Logical Strength, the Test of Relevance, and the Test of Non-Circularity. The tests, which are to be applied in a particular order, must all be passed if an argument is to be worthy of accep- tance as a demonstration that its conclusion is true or is very probably true. To help with the application of the Test of Relevance, we examined seven common fallacies of relevance. Arguments that manifest these notoriously fallacious approaches to presenting reasons and claims often beguile and mislead us.

fallacies are deceptive arguments that appear logi- cal, but upon closer analysis, fail to demonstrate their conclusions.

then the strategy succeeded. This is only one example of using one’s skills at argument making to achieve one’s goals. Defense attorneys who get juries to acquit crimi- nals is another, as are prosecuting attorneys who get juries to convict innocent people accused of crimes. The ethical question for all critical thinkers is: To what pur- poses ought I to put my powerful critical thinking skills? This question is analogous to the question: To what pur- poses ought I to put my college education? These are, in part, ethical questions and, in part, questions about one’s sense of how to make the meaning of one’s life. And what are your answers? Why?

support your evaluation. State in your own words why the argument is worthy of acceptance, or why it is not a good argument.

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1.

When I stop at a traffic light, I hear this funny rattling sound coming from under my car. It is sort of in the middle or maybe toward the back, but definitely nottoward the front. I only hear it when the car is idling, not when I’m driving along at a reasonable speed. My dad said once that the metal baffles inside a muffler can loosen up if the muffler is old and rusty. He said that a loose baffle makes a rattling sound when it vibrates, like when the engine is idling or when the tires are out of alignment. My muffler is at least nine years old. So, I’m thinking that probably the rattling sound is coming from the muffler.

2. In a perfect world, the government should investigate whether any laws were broken relating to the treatment of wartime detainees. But this is not a perfect world. So, it would be a mistake for the government to engage in such an investigation.

3. Having turned up some new information, a cold case homicide detective interviewed the victim’s husband some years after his wife’s death. The distraught husband said, “I have been praying all these years, asking God to send us something. My wife’s murder could not have been simply a random accident. God would not permit that.”13

4. If God intended marriage for the sole purpose of human reproduction, and if same-sex couples are entirely incapable of human reproduction, then it follows that God did not intend marriage for same- sex couples.

5. As you all know, there has been a successful Chinese experiment that used a single cell from a laboratory rat to generate a living chimera of that rat. In the chimera, which lived to adulthood, 95 percent of its genetic material was identical to the donor rat. Noted cell biologist Dr. Kastenzakis believes tinkering with nature is just what scientists do. Therefore the Chinese experiment raises no ethical questions and poses no ethical risks.

6. In the past whenever the TV news programs in Chicago ran headline stories featuring a sketch artist’s drawing of a fugitive, the Chicago Police Department (CPD) hotline received over 200 phone calls from people all over the city who said that they spotted the person. Tonight the Chicago TV news programs are going to feature a sketch artist’s drawing of a fugitive whom the police are trying to locate. This will probably yield hundreds of calls on the CPD hotline.

7. Suppose we imagine electricity flowing through wires in the way that water flows through pipes. With this analogy in mind, it would be reasonable to infer that wires that are larger in circumference should be capable of carrying greater electrical loads.

8. Former NFL quarterback James Harris tells a story about how he committed to throwing footballs until his arm hurt. Knowing that the NFL regarded

the down-and-out pass pattern as one of the more difficult passes for the quarterback, Harris visited the local park and, while nobody watched, he tested himself. He targeted a tree and threw at it blindfolded. He knew that if he missed, he would have to walk a long way downfield to pick up

the football. And he did miss the first time. So he wondered whether it was a good idea to even try again. But he did try. And when he heard the ball hit the tree that sound gave Harris a ton of confidence.14

9. My client did not intend to use the weapon, and so he is not guilty of armed robbery. Yes, we agree with the prosecution that he committed the robbery. And, yes, we agree that he was carrying a weapon and that he brandished the weapon to intimidate the store clerk and the customers. We agree that the law reads, “Anyone who carries a weapon in the commission of a robbery shall be guilty of armed robbery.” And, yes we admit that he shouted, “Everyone down on the floor or I’ll shoot.” But, and here is the key fact, the weapon was not loaded. He did not have ammunition anyplace on his person or in his possessions. He never intended to use that weapon. And, therefore, the crime that he is guilty of is robbery, but not armed robbery.

10. Look, officer, you can’t arrest me on felony rape charges just because she’s 17 and I’m 21. Yes we had sex. But it was consensual. And anyway, in two weeks she’s going to be 18, and we plan to get married.

11. I like the President’s approach to trade with China, and I haven’t heard anyone give any evidence that his approach is not going to be effective. So, it must be the right thing for our country to do at this time.

12. Not every argument is of equal quality. Therefore, at least one argument is better than at least one other argument.

using all four tests, evaluate argument worthiness and explain: Evaluate the following arguments using all four tests, applied in their proper sequence. In each case, give a detailed explanation to support your evaluation. State in your own words why the argument is worthy of accep- tance, or why it is not a good argument.

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1.

Being a sports writer offers challenges that writing standard news stories do not. Here’s why. Unlike with standard news stories where the writer is telling the reader something that the reader does not yet know, most of the time the reader knows who won the

game before reading your article. Readers probably watched the game on TV. This means a sports writer has to find some angle or some clever and captivating way of telling the story. . The Seattle Post-Intelligencer and Denver Rocky Mountain News are going to close unless they find a buyer. Same for the San Francisco Chronicle and the Miami Herald. The Minneapolis Star-Tribune may file for bankruptcy. The Los Angeles Times Sunday edition has shrunk to half its former size. And the list of newspapers in financial trouble goes on and on. I think it is safe to

say that the newspaper business may be dying.

3. Torturing prisoners of war often results in poor- quality intelligence. Experience has shown that people in pain will say anything to get the pain to stop. The pain can be either physical or psychological—it does not matter. People crack under the pressure of an experienced interrogator using torture methods. So, we cannot trust the information that comes from that source.

4. Torturing prisoners is against the Geneva Conventions, but it can be a useful means of gathering potentially valuable intelligence. There have been cases where the information given to us by prisoners who have been repeatedly waterboarded, for example, has turned out to be correct. Therefore, we are justified in using torture on prisoners even if our laws explicitly prohibit such methods.

5. More than transferring genes from one organism to another, biologists have successfully engineered synthetic chromosomes into yeast, replacing 16 original chromosomes.15 Our species now knows how to alter the DNA of living cells using synthetically manufactured chromosomes. Synthetic bio-engineering makes possible new biofuels,

new medicines, and other genetic improvements.

Group Exercises

should duI homicide be prosecuted as murder? What do others think? This exercise works best with a five person group. Each member of the group, having seen the 60 Minutes video and worked on the individual exercise will

Therefore this landmark scientific achievement is a very good thing.

6. Morethantransferringgenesfromoneorganism to another, biologists have successfully engineered synthetic chromosomes into yeast, replacing 16 original chromosomes. Our species now knows how to alter the DNA of living cells using synthetically manufactured chromosomes. Synthetic bio-engineering is tampering with nature in a way that goes beyond all previous methods. Nobody knows what damage might be done to our species and to other animals and plants. Therefore this landmark scientific recklessness is a very bad thing.

should duI homicide be prosecuted as murder? What do you think? A prosecuting attorney in New York is bringing charges of murder against individuals who have killed other people while driving under the influence. The attorney argues that everyone understands that driving while under the influence poses risks for the driver and for other people, including the risk of a fatal accident. The statutes provide for charges of “depraved indifference” when one’s behavior results in the unintended but fore- seeable death of another human being. Defense attorneys argue, among other things, that the laws pertaining to murder were never intended to be applied in this way. The debate was captured by CBS’s 60 Minutes in a segment that aired on August 2, 2009. Search "Should DUI Homicide be Prosecuted as Murder 60 Minutes" to locate and watch that segment. Map out the reasoning for both sides of this debate. Evaluate the reasoning using the four tests for evaluating arguments. After completing your evaluation, present your own reasoned views on the matter. than a textbook’s abstraction. So you and the other mem- bers of your group need to focus on what you hear in the interviews without letting your personal opinions get in the way.

Your group will conduct four sets of interviews. You must always have at least two members of your group par- ticipate in each interview. This is so that you can help each other remember what the person being interviewed said.

First set of interviews: Locate at least one person— two or three if possible—who has been arrested for driv- ing while under the influence of alcohol or drugs even if not for homicide. Find out what that person or those peo- ple think. Listen to their arguments, and then write them down and evaluate those arguments. Be objective and fair-minded in your evaluation, regardless of whether you agree or disagree with the person’s position.

Second set of interviews: Locate at least one person— two or three if possible—who is a former drinker. Interview that person the same way. Get his or her views on the matter, write down the person’s arguments, and evaluate those arguments objectively and fair-mindedly.

Next, contact Mothers Against Drunk Driving (MADD) or some other volunteer organization that is known for its stance on issues relating to drunk driving. Follow the same drill. Get that organization’s arguments down and evaluate them.

Finally, contact the office of your local prosecuting attorney, or the state police and, again, conduct your inter- view and evaluate the arguments you hear.

Having talked directly with people who are close to this issue, your group must now assemble all the argu- ments that came forward in the various interviews. In light of these perspectives, take a stance individually and as a group on whether or not homicide by DUI should be prosecuted as murder. Write out the group’s opinion and give the reasons. Write out your individual opinion, if you disagree, and give your reasons. Whatever you finally decide, use strong critical thinking and sound reasons.

assisted suicide: Assisted suicide is legal in Oregon and in Sweden, but not in many other places. There are argu- ments pro and con. Begin this exercise by familiarizing yourself with those arguments. Map and evaluate the most common arguments on both sides. Then interview two or more people over the age of 60, two or more peo- ple between the ages of 18 and 30. With their permission, record the interviews so that you can check the accuracy of your analysis and interpretation of their perspectives. Ask each person to consider whether or not they would agree with a law that permitted a competent adult to seek and to receive suicide assistance from a licensed health care professional, if that adult knew with a very high level of confidence that she or he had a medical condi- tion that would result in painful death in less than three months. Map and evaluate, using the four tests of the worthiness of arguments presented in this chapter, the set of arguments you collect from the eight people. Is there a pattern?

CHAPTER 8

You need a liver lobe now! Imagine that you, like 78,000 other Americans each year, overdose on acetamin- ophen, the active ingredient in Tylenol. Imagine you are one of the 33,000 whose overdose is so severe that you are rushed to the hospital.1 You go into acute liver fail- ure. Fortunately you survive. Your liver, however, does not. You need an organ transplant. Specifically, you need a liver lobe. You have three and only three options: You must get on the waiting list here in the United States and hope that you do not die before a donor liver is found for you. Your second option is to travel overseas where you can be assured of receiving a liver transplant. Your third option is to die. But, let’s assume that you cannot be put on the waiting list for a liver here in the United States because you have other medical issues. Disqualified from the wait- ing list option, that door is closed. And let’s assume that you do not want to die. So Door #3 is closed. The only pos- sible conclusion from this set of assumptions is that you have but one option: travel overseas where you can be

Deductive Reasoning

To learn to think well we must accept the challenge of digging deeply into core ideas and key questions.

The core idea in Chapter 8 is this: An important group of inferences logically require that their conclusion must be true if

assured of receiving a liver transplant. Apart from chang- ing the premises, there is no logical way of escaping that conclusion. Of course, that conclusion implies an ethically repugnant result, which is that you must now become a buyer in the international marketplace for human organs. The liver lobes sold in that marketplace are harvested from healthy but desperate people living in abject poverty who sell their body parts to feed their families. (To learn more, search and watch “Tales from the Organ Trade,” an HBO documentary.2)

In this chapter and the next, we will be refining our argument evaluation skills. Here our attention will be on arguments that are structured in such a way that their premises guarantee the truth of the conclusion. In every- day language we would say that the premises imply the conclusion or entail the conclusion, meaning that there is no possibility that all the premises could be true and the con- clusion false. The opening scenario is structured so that you have exactly three possible options. But two of them

turn out to be closed to you. Therefore we can infer with certainty that your one and only choice is to go overseas for the organ transplant. The situation is structured like this: There are only three doors: #1, #2, and #3. You must select one of the three doors. Door #1 is nailed shut and so is Door #2. Therefore Door #3 is your only option.

If the assumption that all the premises are true makes it impossible for the conclusion to be false, that is, if the prem- ises entail or imply that conclusion, we will evaluate that argument or inference as valid.3 Needless to say, a valid argument passes the Test of Logical Strength. In this chapter we will learn how to recognize valid arguments by the way the inference is structured and we will consider a group of common fallacies that masquerade as valid inferences.

8.1 The Structure of the Reasoning

One important distinguishing feature of valid arguments is that if the conclusion is false, then one or more of the premises must also have been false.

Consider MAP #1, which shows the structure of the organ transplant scenario. Trace the reasoning backward, against the flow of the arrows. What can we infer if we assume that the claim “I must go overseas for a trans- plant,” is false? That may mean that you decided to accept your fate and embrace death. If so, then the premise “I want to live” has turned out to be false. Or perhaps you were invited to join a clinical trial for a newly invented synthetic liver. If so, then the premise “A transplant is my only option” is false. Or maybe you received the unex- pected news that the US organ donor policies had been changed so that you could now be put on the waiting list. If so, then the premise “I am not eligible for a transplant in the United States” is false. Or maybe your physician calls to say that your liver function has unexpectedly improved to a level that you no longer require an immediate trans- plant. In that case the starting point assertion “I need a

liver lobe now” is false. This is an example of the principle that if the conclusion of a valid argument turns out to be false, then one or more of its premises must be false too.

As they say in the TV infomercials, “But wait! There’s more.” Suppose you are so distressed about needing to go overseas for a liver transplant that you cannot sleep. Late one night you see a commercial that promises a “miracle cure.” For only $19.95 plus shipping you can buy “liver seeds.” The hawker, dressed in a white lab coat, says “these seeds take root in your body and grow into a healthy new liver.” The hawker goes on, “Yes, this is the first truly sur- gery free transplant!” Wow, have we found something that makes the conclusion false but permits all the premises to still be true. No. Even this ridiculousness makes the prem- ise “A transplant is my only option” false. Remember don- key cart words from another chapter? The bogus “truly surgery free transplant” is not a transplant in the standard medical definition of that term. What changed is the struc- ture of the argument. Adding the “miracle cure” is like adding the clinical trial option, it alters the structure of the reasoning by creating Door #4.

Inferences Offered as Certain

“Aristarchus deduced that the Sun was much larger than the Earth,” explains Carl Sagan in the 1980 Cosmos series.4 We often attribute the idea that the Earth is a planet revolv- ing around the Sun to the fifteenth-century Polish astrono- mer–priest named Copernicus. But, in fact, the first scientist known to have reasoned with certainty to a Sun-centered view of the solar system was the Greek astronomer– mathematician Aristarchus (310–230 bce). More than two millennia earlier than Copernicus, and using no telescope, but only his own eyes and the then newly invented math- ematics we call Geometry, Aristarchus considered the size of the Earth’s shadow on the Moon during a lunar eclipse. He then concluded that the only possible explanation for the size of the shadow of the Earth on the Moon during a lunar eclipse was that the source of light shining toward the Earth and the Moon from a very great distance away

must itself be of immense size. Must be. We are not talk- ing high degrees of probability here. This was certitude. If you assume that light travels in a straight line, and if you know anything about shadows, then you must infer with certitude that the Sun is gigantic as compared to the Earth and that it is very much further from the Earth than is our Moon.

There are times, perhaps not many, when a person makes an argument believing that truth of the prem- ises completely guarantees the truth of the conclusion.5 The Sagan quote in the Aristarchus example is one such instance. Sagan meant that there was no other possible explanation, no other inference Aristarchus could draw except that the Sun was very large and very far away. One important caution, however. Thoughtful and fair- minded interpretation is important. People do not always speak with the logical precision Sagan used. So we need to keep in mind the context and the intention of the argument maker. Strong critical thinking requires that we not attribute more than the argument maker intends. A friend of ours uses the expression “that must be what happened” when he means only “that is prob- ably what happened.”

Although at times we all have wished otherwise, none of us can suspend the laws of nature or the laws of logic. In business, a company that is losing money may have absolutely no choice but to lay off good employees. In a medical emergency, health care professionals have to decide which of the victims to treat first, knowing that they cannot get to everyone in need. Military leaders have to send brave soldiers into combat knowing with certainty that there will be casualties. Regardless of our feelings in the matter, there are times in our lives when the facts and

the logic of a given situation force us to entertain options we had hoped never to face. In those situations we can- not afford to be wrong about the facts or about the logical strength of our reasoning.

In this chapter we will assume that the examples are inferences and arguments presented to show that their conclusions must be certain, given the premises. From the perspective of building critical thinking skills, the impor- tant question is how to evaluate the logical strength of an infer- ence or argument offered as certain. Because the argument maker is asserting that there is no possibility whatsoever that the premises could all be true and yet the conclusion turns out to be false, our evaluative task is clear. If we can come up with a counterexample, namely a scenario in which all the premises are true but the conclusion is false, then the argument is not valid. It is not logically certain! Given that counterexample, we know that the premises do not imply the conclusion.

Because this chapter focuses on the Test of Logical Strength only, we will assume that the examples used here have already passed the Test of the Truthfulness of the Premises. This will be a lot to swallow, because some of the premises are patently false. But, for the educational purpose of focusing on the logic strength of the example arguments, let us entertain the fiction within the context of this chapter.

It is the mark of an educated mind to be able to entertain a thought without accepting it.6

Aristotle, Philosopher, Physicist, & Zoologist (384–322 bce)

Reasoning with Declarative

Statements

The first group of valid argument templates7 we will con- sider include those that derive their valid structures from the way simple statements interact grammatically when we use prepositions or adverbs that have logical force. These include the words and, or, not, and if . . . then. . .

Denying tHe Consequent8 One valid argument tem- plate we rely on regularly produces arguments structured like this:

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Premise #1: Premise #2: Conclusion:

If A, then B. Not B, Therefore, not A.9

The argument template uses the capital letters A and B to stand for simple positive declarative statements, like A = “the city has a reliable public transportation sys- tem.” And B = “i will use the city’s public transportation system.” Substituting those two statements in the template

for A and for B produces this argument:

• Premise #1: if the city has a reliable public transpor- tation system, then i will use the city’s public trans- portation system.

• Premise #2: It is not the case i will use the city’s pub- lic transportation system.

• Conclusion: Therefore it is not the case that the city has a reliable public transportation system.

In each of the examples below, the blue statement is A and the orange statement is B. Here are three more exam- ples of valid arguments built by substituting declarative statements into the Denying the Consequent argument template.

• if Richard graduated with honors, then Richard maintained a gPA of 3.2 or higher. It is not the case that Richard maintained a gPA of 3.2 or higher.

Therefore, Richard did not graduate with honors.

• If you have been promoted to the rank of captain, then you have served for at least a year. you have not served for at least a year. It follows then that you have not been promoted to the rank of captain.

• If the sun shines on the far side of the moon, then red roses grow inside the barns in iowa. It is not true that red roses grow inside the barns in iowa. So, it is not true that the sun shines on the far side of the moon.

This last example is curious because it is structurally valid, but in fact we would not rely on it as a proof that the sun does not shine on the far side of the moon. The argu- ment is not acceptable because even if it were true that no red roses grew in any Iowa barns, the first premise is not true. This example is a quick reminder that logical strength, while essential, is not the only consideration that strong critical thinkers have in mind when evaluating arguments in real life. Again, in all the examples here and to follow we are maintaining our focus on the logic while assuming that all the premises are true.Yes, it can be challenging to assume that the premises are true, but that is why we separated the Test of the Truthfulness of the Premises from the Test of Logical Strength. Facts and logic are two different things.

Using short declarative statements fill in the argu- ment template to create two valid Denying the Consequent examples of your own.

If ,then . It is not the case that .

Therefore it is not the case that . If , then . It is not the case that . Therefore it is not the case that .

AffiRming tHe AnteCeDent10 A second very com- monly used argument template also relies on the meaning and grammatical power of “if..., then...” expressions. In this case, however, the second premise affirms that the “if” part is true.

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Premise #1: Premise #2: Conclusion:

If A, then B. A. Therefore, B.

Here are three arguments that are valid on the basis of affirming the antecedent argument template.

• If the price quote from College insignias is lower than the price quote from university Logos, then we will get the t-shirts for our ACs Relay for Life team printed at College insignias.

the price quote from College insignias is lower than the price quote from university Logos.

Relay for Life team marching to support American Cancer Society.

Therefore, we will get the t-shirts for our ACs Relay for Lifeteam printed at College insignias.

• If you are eligible to graduate with honors, then you will receive notification from the Registrar. you are eligible to graduate with honors. So, it follows that you will receive notification from the Registrar.

• If the sun shines on the far side of the moon, then carrier pigeons get high in Denver. the sun shines on the far side of the moon. So, carrier pigeons get high in Denver.

As with pre-algebra, we are substituting values for the variables in the formula. In pre-algebra the result was an

equation; here the result is a valid argument. Using short declarative statements, fill in the Affirming the Antecedent argument template to create two valid examples of your own.

The next example is a variation on the second. Instead of the first alternative being eliminated so that the second emerges as the only remaining option, in this case the sec- ond alternative was eliminated so that the first emerged log- ically as the only remaining option. The template for this is:

•

•

If , then . .

Therefore, .

If , then . .

Therefore, .

Premise #1: Premise #2: Conclusion:

Either A or B. Not B. Therefore, A.

DisjunCtive syLLogism When we are presented with various alternatives and then learn that one or more of those alternatives will not work, it is logical to reduce our options. The argument template for this valid structure produces arguments with this pattern:

• Either i’ll take organic chemistry over the summer, or i’ll take that course next fall. There’s no way i can take that course next fall. So, i’ll take organic chemistry over the summer.

In context “that course” refers to organic chemistry. In actual practice, when we make arguments, we seldom repeat statements verbatim. Instead, we use internal refer- ences that are contextually unproblematic.

The chapter “The Logic of Declarative Statements,” extends the discussion above into the discipline of Logic. That chapter presents a method for expressing the key logi- cal relationships between simple declarative sentences using symbols. And it provides a surefire way of evaluating the validity of arguments expressed in that symbolic notation.

Reasoning about Classes of Objects

Other arguments derive their valid structures from the meanings of words in the language used to show the inter- action of groups of objects. Words like some and all are used to express our ideas about how individual objects and groups of objects relate.

Premise #1: Premise #2: Conclusion:

Either A or B. Not A. Therefore, B.

Here are two examples of arguments that are valid by vir- tue of the Disjunctive Syllogism argument template.

• Either we’ll go to miami for spring break, or we will go to myrtle Beach. we are not going to miami for spring break. So, we will go to myrtle Beach.

• Either i’ll take organic chemistry over the summer, or i’ll register for that course next fall. No way will i take organic chemistry over the summer. So, i’ll register for that course next fall.

APPLying A geneRALizAtion Consider this example of reasoning about individual objects and groups of objects:

• All the books by Michael Connelly feature his fictional hard-boiled LAPD detective, Hieronymus Bosch.11 Echo Park is a book by Michael Connelly. So, Echo Park features Detective Bosch.

In this example the first premise states every member of a class of objects (books by Connelly) has a specific attri- bute (features Detective Bosch). The second premise iden- tifies a specific member of that class (Echo Park). And the conclusion that follows necessarily from those two premises is that Echo Park features Detective Bosch. Whenever we have a generalization that asserts that a given characteristic applies to each of the members of a class of objects, we can logically assert that a given individual or subgroup of individuals that are members of that class has that characteristic. For example:

• Everyone who installs attic insulation runs the risk of inhaling potentially harmful dust and fiberglass particles. Angela and Jennifer install attic insula- tion. This means that both of them run that risk.

• Every young woman living in a Muslim coun- try who played in a successful Western style rock band was subjected to numerous hate mes- sages, slurs, and death threats. The young women Aneega, Noma, and Farah lived in a Muslim country and played in the successful Western style rock band known as Pragaash. So Aneega, Noma, and Farah were subjected to numerous hate mes- sages, slurs and death threats.12 [In this case the

premises are true. The grand mufti Bashiruddin Ahmad declared a fatwa on the band and advised its Muslim members to sing only inside their homes to the other female members of the family, and to wear veils when going out in public.13]

If F and G stand for classes of objects, and if X stands for an individual object, then the argument template for Applying a Generalization would work like this:

Premise #1:

Premise #2: Conclusion:

Every member of group f is a member of group g. Individual object X is a member of f. So, the object X is a member of g.

APPLying An eXCePtion If we know that every mem- ber of a given class of objects has a certain characteristic, and we also know that one or more specific objects do not have that characteristic, we can logically infer that they are not members of that class. For example:

• Everyone who waits tables has experienced the chal- lenge of trying to be respectful to a rude customer. Alex has never experienced that challenge. That implies that Alex has never worked as a waiter.

• Everyone who works as an attic insulation installer risks inhaling potentially harmful dust and fiberglass particles. Angela and Jennifer have jobs that do not put them at risk for inhaling anything that is poten- tially harmful. So, Jennifer and Angela do not install attic insulation.

• The numbers 5, 7, 13, and 37 are not divisible by 2 without a remainder. Every even number is divisible by 2 with no remainder. So, 5, 7, 13, and 37 are not even numbers.

The argument template for Applying an Exception works like this:

Now watch how the meanings change depending on where only is positioned.

Here is another example, but this time you fill in the left-hand side of the table by showing where the word only would be located to enable the interpretation on the right.

Location of Only to Change Meaning

Interpretation of New Statement

Only some people objected to being forced to attend.

Others people did not object.

Some people only objected to being forced to attend.

They did not quit, go on strike, or boycott.

Some people objected only to being forced to attend.

They would have preferred to have been asked or invited to attend voluntarily.

Some people objected to being forced only to attend.

They wanted to do more than attend; they wanted to participate actively.

•

Some who are students pursue excellence.

Location of Only to Change Meaning

Interpretation of New Statement

Some who are students pursue excellence.

They do nothing but pursue.

Some who are students pursue excellence.

The one thing they pursue is excellence.

Some who are students pursue excellence.

Some students do not pursue excellence.

Some who are students pursue excellence.

They have no other identity besides being students.

Premise #1:

Premise #2: Conclusion:

Every member of group f is a member of group g. The object X is not a member of g. So, the object X is not a member of f.

tHe PoweR of Only Only is one of the most interest- ing words in the language. That word has the power to change the meaning of a sentence depending on where it is placed. Consider this four-part example. Here, first, is a simple sentence:

• Some people objected to being forced to attend.

Reasoning about Relationships

Natural languages are rich with terms that describe relation- ships. We use our understanding of the meanings of these terms to make valid inferences about the objects to which

the terms apply. For example, the arguments below are valid because of the meanings of the relational terms like sibling, brother, sister, shorter than, older than, taller than, younger than, greater than, or equals. Notice that in ordinary discourse it is not necessary to specify generalizations like “Anyone who is a person’s brother is that person’s sibling,” because those relationships are part of the meanings of the terms. Our understanding of the logical implications of relational terms is part of our comprehension of language. We seldom, if ever, attend to the logical complexity embedded in natural language. Here are some examples of valid arguments built on the meanings of the relational terms these arguments use.

• John is Susan’s younger brother. So, they must have the same mother or the same father.

• Fresno is north of Bakersfield. Bakersfield is west of Phoenix. So, Phoenix is southeast of Fresno.

• Six is greater than five. Five is greater than four. Therefore, six is greater than four.

• (4 + 6) = 10. (2 × 5) = 10. Therefore, (4 = 6) = (2 × 5).

tRAnsitivity, RefLeXivity, AnD iDentity Three relational characteristics we rely upon regularly when using valid reasoning are named Transitivity, Reflexivity, and Identity. Here are two examples of valid arguments based on each, beginning with two examples of transitiv- ity, then a description of the transitivity relationship. After each pair of examples, the relationship is described.

Leonardo DiCaprio, Oscar nominated actor

• Tomas is taller than Jose. Jose is taller than Miguel. So, Tomas is taller than Miguel.

• Susan is Joan’s ancestor. Joan is Philip’s ancestor. So, Susan is Philip’s ancestor.

Transitivity Relationship = If x has a transitive relationship to y, and y has the same transitive relationship to z, then x has the same transitive relationship to z.

• David is Stanley’s neighbor. So, Stanley is David’s neighbor.

• Sara is Helena’s roommate. So, Helena is Sara’s roommate.

Reflexivity Relationship = If x has a reflexive relationship to y, then y has the same reflexive relationship to x.

• Leonardo DiCaprio played Jordan Belfort in the 2013 film The Wolf of Wall Street. The actor who played Jordan Belfort in that film was nominated for an Oscar. So, Leonardo DiCaprio received an Oscar nomination for his performance in that film.

• The President of the United States was assassinated in 1963. People still remember where they were and what they were doing when they heard that shocking news. John F. Kennedy was the President who was killed that tragic November day in Dallas. So, people still remem- ber where they were and what they were doing the day they heard that Kennedy had been assassinated

Sir Arthur Conan Doyle’s famous detective calls the arguments he put forth with certainty “deductions.” He describes the process of deductive reasoning this way:

“Eliminate all other factors, and the one which remains must be the truth.”

Sherlock Holmes14

8.2 Fallacies Masquerading as Valid Arguments

Just as there are valid argument templates, there are falla- cious argument templates. Analysis of the meanings of the terms used and the grammatical rules of the language reveal the source of the error. Precision of thought and expression is the key to avoiding these mistakes when making or evaluat- ing arguments offered as valid inferences. Often, a counter- example that mirrors the fallacious argument template will have the power to reveal the illogical structure, expose the fallacy, and squelch the argument’s apparent persuasiveness. As before, in this section please assume that the premises of the example arguments are all true, so that we can focus on their logical flaws rather than their factual inaccuracies.

Fallacies When Reasoning with

Declarative Statements

We saw that affirming the antecedent and denying the con- sequent were two logically correct ways of reasoning with declarative statements. There is a pair of familiar fallacies that mimic those logically correct templates.

AffiRming tHe Consequent Suppose it is true that “If the river continues to rise, then the carpet will get wet.” And suppose that we observe that the carpet is wet. It does not follow that the water that wet the carpet came from the river. The wetness may have come from an entirely different source, for example, the dishwasher overflowing, a pitcher of water being spilled, rain coming in an open window, or even old and sadly confused Uncle Joe bringing in the garden hose yet again to water the sofa with flower-patterned upholstery.

The fallacy of Affirming the Consequent follows this invalid pattern:

But A may not be the only condition that brings about B. So, it does not make logical sense to believe that A must be true simply because B is true. Here are more examples of the fallacy of Affirming the Consequent.

• if we put an American on mars before the end of the twentieth century, then we have a successful space program. we do have a successful space program. So it must be true that we put an American on mars before the end of the twentieth century.

• If i am a good person, then god favors me with friends, wealth, and fame. god has favored me with friends, wealth, and fame. Therefore, i must be a good person.

Denying tHe AnteCeDent Suppose the same hypo- thetical as before: “If the river continues to rise, then the carpet will get wet.” And suppose that we receive the good news that the river has crested and is now receding. It does not follow that the carpet will not get wet. We still must contend with the leaky dishwasher, the open window, and dear old Uncle Joe, the sofa watering man.

The fallacy of Denying the Antecedent follows this invalid pattern:

JOURNAL

It’s Elementary!

Is it even possible to follow the advice of Sherlock Holmes on how to figure out the one right answer to a problem? Explain.

Premise #1: Premise #2: Conclusion:

If A, then B. Not A. Therefore not B.

Premise #1: Premise #2: Conclusion:

If A, then B. B. Therefore, A.

As before, A may not be the only condition that brings about B. So, it does not make logical sense to think that just because A does not happen, B cannot happen. Here are two more examples of the fallacy of Denying the Antecedent.

• If everyone who lived in mississippi drank red wine daily, then the wine industry would be booming. But some mississippians never drink red wine. So, the wine industry is not booming.

• If we see a light in the window, we know that there is someone at home. But we do not see a light in the window. So, no one is home.

Fallacies When Reasoning

about Classes of Objects

Just as there are logically correct ways of reasoning about classes of objects and their members, there are familiar mistakes we often hear being made. Here are examples of fallacious reasoning about classes of objects. These com- mon errors have earned their own names.

fALse CLAssifiCAtion Suppose “Criminals enjoy mafia movies” and “Cassandra enjoys mafia movies” are both true. It does not follow that Cassandra is a criminal. The same feature or attribute can be true of two groups or two individuals without requiring that one group must

be classified as part of the other group or that the two indi- viduals must be grouped together in all ways. The facts that Emile attended the campus concert and so did 50 stu- dents from the local high school does not make Emile a high school student.

Here are three more examples of the False Classification fallacy.

• A good number of residents of Iowa enjoy reading popular fiction. Some who enjoy popular fiction also enjoy windsurfing on their local beaches. So, a good number of residents of Iowa enjoy windsurfing on their local beaches.

• The police profiler said that the rapist was a white male, age 25–35, and aggressive. The suspect is a white male, 28 years old, and aggressive. This estab- lishes that the suspect must be the rapist.

• There are ways of telling whether or not she is a witch. Wood burns and so do witches burn. So how do we tell if she is made of wood? Well, wood floats. And ducks

float. So, if she floats, then she weighs the same as a duck and therefore she is made of wood. And there- fore . . . , she is a witch! (Condensed from Monty Python and the Holy Grail Scene 5: “She’s a Witch,” 1975.)

Millions have enjoyed the humor that Monty Python created out of this fallacy in the famous “She’s a Witch” scene from Monty Python and the Holy Grail. If you Google "Witch Monty Python" chances are you will find the scene.

The Monty Python knight’s reasoning implies certain death for the poor woman accused of witchcraft, but only if all three premises are true.

Premise #1: If she floats, then she is a witch and we shall burn her. Premise #2: If she does not float, she’ll drown. Premise #3: Either she will float or she will not float. [Unspoken.]

Conclusion: Ergo, she dies.

fALLACies of ComPosition AnD Division

Reasoning about the relationships of parts and wholes can appear to be valid, but fail because the attribute that

Valid Inferences 169 applies to the parts may not apply to the whole, or vice

versa. Here are some examples:

• It is in each person’s financial interest to cheat a little on his or her income tax return. So, it is financially good for the nation if people cheat on their taxes.

• No muscle or joint or organ or cell in your body has the right to give its individual informed consent to a medical procedure. So, why should you, who are com- posed entirely of those many parts, have such a right?

In the first example, an attribute of individual peo- ple who pay taxes is being illogically attributed to the class of objects (“the nation”). The good of each is not necessarily the good of all. The second attempts to with- hold from individuals the right to give informed con- sentbecausenoneofourbodypartshavethatright. These examples of the Fallacy of Composition, so called because these fallacious arguments err by reasoning

that a group has exactly the same attributes that each of its members have. “I don’t know, Bill. Everyone on the Budget Committee is really smart. But, wow, that Committee makes stupid decisions. How can that be?” Simple. What is true of individuals is necessarily true of groups, including how well the group performs. Now consider these three examples:

• The president of the large corporation sent a memo to every vice president, director, manager, and supervi- sor saying, “In corporations of our size with hundreds of employees we can be certain that 10 percent of our total workforce is performing at a substandard level. Therefore, I am directing everyone in charge of a unit of 10 or more people to immediately terminate one person of every 10 in the unit. Forward the names of your substandard employees to Human Resources by 5:00 pm tomorrow.”

• The United States of America has the right to enter into treaties and to declare war. Therefore each of the 50 states has the right individually to declare war or to enter into treaties.

• The average class size at the university is 35 people. Therefore, every class you are taking this term must have 34 other people enrolled in it.

These three examples illustrate the Fallacy of Division, which is the same error, but committed in the opposite direction. Fallacies of Division attribute to each individual member of a group a characteristic that is true of the group as a whole. In the first, an attribute of the class of objects known as the corporation’s total workforce is being illogi- cally attributed to each individual small department or unit. In the second, an attribute of our nation as a whole— the authority to enter into treaties—is being ascribed to each of the states that form our nation. In the third, the average class size, which is an attribute of the university, is illogically attributed to each and every class being offered, as if small seminars and large lectures did not exist.

Fallacies of False Reference

Fallacies of false reference occur when reasoning about relationships like identity, reflexivity, or transitivity these most often occur when people think they are talk- ing about the same thing, but in fact are not. The ambi- guity of the expressions like “When did we see it?” or “I did it yesterday.” can be the source of a mistaken infer- ence if different people interpret “it” to be referring to different things. In another chapter we used an example from My Cousin Vinny to illustrate the miscommunica- tion that can arise out of just such an error. In that film the sheriff thought that a young man was confessing to murder when, in fact, he was only saying that he had inadvertently shoplifted a can of tuna fish. A comparable

reasoning mistake occurs when people are not aware that the same object, person, or event may be identified using multiple descriptions.

Suppose that “The dean knows that this year the School of Engineering award for Best Senior Project should go to Team Steelheads.” And suppose that “The four mem- bers of the team are Karen, Anna, Dwight, and Angela” is true. It does not follow that the dean knows that Karen, Anna, Dwight, and Angela are winners of this year’s award. Why? Because the dean may not know that they are the members of Team Steelhead. Knowing, believing, wanting, or intending something when it is described or named in one way does not imply that the person neces- sarily knows, believes, wants, or intends that very same thing as described or named in another way. That is, unless we add that the person is aware that the two descriptions actually refer to the same thing. Here are two more exam- ples of the fallacy of False Reference.

• Tyler at age 10 has often told his Mom that in col- lege he wants to learn how big buildings and bridges are built. These are subjects addressed in civil engi- neering. Therefore, Tyler has announced that he plans to major in civil engineering in college. [No. Young Tyler has no idea what "civil engineering" is.]

• Anthony heard that a winner of the 2010 Tour de France used banned performance-enhancing sub- stances. The winner of the 2010 Tour de France is Andy Schleck. Therefore Anthony heard that Andy Schleck used banned performance-enhancing sub- stances. [It is not logical to suppose that Anthony knows anything about the cyclist Andy Schleck, including that he is the 2010 winner. As it happens, however, we cannot leave this example without clari- fying something. Andy Schleck is the winner of 2010 Tour de France. But he was awarded the win after Alberto Contador, the original winner, was disquali- fied for doping.15]

Personal Infallibility?

We Don’t Think So

Relying on the grammatical structures of our language, the meanings of key terms, and the laws of mathematics and physics our powers of reasoning enable humans to achieve wondrous technological, computational, and engineering successes. Our species is capable of inferring with certainty the implications of rules, laws, principles, and regulations. This same capability provides endless hours of enjoy- ment working puzzles and playing games like Sudoku, Spider solitaire, Go, and Chess. The structures defined by the rules of those games determine with certainty the choices we can make as players and the outcomes of each possible choice.

Summing up this chapter,

when a person offers an argument believing that the truth of the premises completely guarantees the truth of the conclusion how might we evaluate the logical strength of that argument? The answer is clear: If we can find a coun- terexample, then the argument fails to show that its con- clusion must be true given the truth of the premises. But, if there is no possible scenario in which the premises all are true and the conclusion false, then we would say that

Key Concept

valid describes an argument or inference such that the truth of the premises entails or implies that conclusion

Applications

Reflective Log

getting the Problem wrong: The risks associated with what the Fallacy of Affirming the Consequent (which we renamed in honor of the TV character “The House M.D. Fallacy”) were the extra expense, unnecessary trauma, and risk of death associated with mistaken diagnosis. Review that Thinking Critically box and think about whether you might have ever committed that fallacy or whether you

But our power to reason with certainty can have more ominous results too. At times, like a freight train thundering recklessly down the tracks, our capacity for certainty drives us headlong toward conclusions that turn out to be patently wrongheaded. We are cer- tain that our assumptions imply those conclusions, so we move ahead perhaps not thinking about whether those conclusions make any sense in their own right. Consider, for example, the ideologically based reason- ing used to perpetuate the deprivation and abuse of women and girls.16

How can we prevent that ideological freight train from reaching the wrong destination? The answer lies at the starting point. Are all of our beliefs, values, assump- tions, and interpretations true? A healthy sense of skepti- cism, the study of human history, and a great deal of life experience suggests that the probability of personal infal- libility approximates zero. Even the most learned, saintly, and wise among us can be mistaken. The chapter on Ideological Reasoning takes up this important theme as it explores the captivating certainty and the often dreadful outcomes our species derives from ideological reasoning.

the premises do imply or entail the conclusion. In that case we describe the argument as valid. Because validity depends on the meanings of structure of the argument, including the words and the grammar of our language, we first examined a number of valid reasoning templates. Then, to arm ourselves against their tempting deceits, we reviewed a roster of fallacies that masquerade as valid arguments.

evaluate arguments: Determine which of these arguments are valid and which are fallacious. In each case assume that all the premises are true, even if it strikes you that one or another of them is actually rather implausible. In each case indicate which valid argument template or which fal- lacy is exemplified.

1. Everyone who owns a car needs car insurance. Joe just purchased a car. Therefore Joe needs car insurance.

2. Gatorade® is thirst quenching. Tap water is thirst quenching. So Gatorade is tap water.

3. If we drive on the Pacific Coast Highway near San Francisco we can see islands off the Pacific Coast. We can see islands off the Pacific Coast. So we are driving on the Pacific Coast Highway near San Francisco.

4. “I believe the one who brings the hotdogs is supposed to bring the buns too. Somebody messed up,” said John. “So, what you’re saying is that my mother messed up,” said Mary.

5. There are a lot of repossessed condos on the market. The one on Maple Street is less expensive than the place we saw on Palm Ave. And that cute one on Oak Blvd. is priced even lower than that. So the most expensive of the three is the place on Maple.

6. Tweetsareshort,atmost140characters.Icountedthe characters in your last e-mail and there were 1,400. That implies that your last e-mail is nothing but 10 tweets.

7. “Eitherwe’llfinishtheyardworkintimetogotothe movie, or we’ll enjoy a quiet evening at home,” said John. “I don’t see us finishing in time for the movie,” said Malaya. “It’s a quiet evening at home then,” said John.

8. If Pepsi tasted better than Coke, then more people would select Pepsi in a blind taste test. And that’s just what happened. So, it must taste better.

9. If Pepsi tasted better than Coke, then it would outsell Coke. But Pepsi does not taste better than Coke. So it will not outsell Coke.

10. If the tuition goes up next year, then next fall the freshmen class enrollment will drop. But the freshmen class enrollment will be as high as ever next fall. Therefore next year the tuition will not increase.

Devil and angel: Having died, you find yourself in a room with no windows. You see two identical doors in front of you. There is someone guarding each door. The two guards are wearing identical uniforms. They look exactly alike. A voice, which you recognize as the voice of God suddenly fills the room. God says, “Welcome. An angel guards the door to Heaven. A devil guards the door to Hell. The angel never lies. The devil never speaks the truth. You may ask only one guard only one question. If you ask correctly, the door to Heaven will be opened for you. Good luck, I hope to see you soon.” What one question do you ask to identify the door to Heaven with absolute certainty? To see this puzzle worked out watch, after searching, the epi- sode of the Ricky Gervais Show that HBO broadcasted on January 28, 2011.