Part III. Logical Reasoning: Picking Apart an Argument

Chapter 9. Strengthening and Weakening Arguments

In This Chapter

 Analyzing different types of logical reasoning questions

 Tackling strengthen/support questions

 Taking on weakening questions

 Finding the EXCEPTions

When a lawyer argues a point, she must support it with evidence. Her opponent argues the opposite point, and she must find evidence that can weaken his argument. Law students take an entire class on evidence in which they explore how to use evidence to support their cases or to destroy the other side's evidence. Using evidence to support arguments is a constant requirement in all their other classes. To succeed as a law student and a lawyer, you absolutely must have a good understanding of how evidence can strengthen or weaken a conclusion.

The LSAT-writers design logical reasoning questions to test your ability to strengthen or weaken arguments. These questions present an argument and then ask you to strengthen it, weaken it, criticize it, or some other similar exercise.

In this chapter, we show you how to identify strengthen/weaken questions and provide strategies for working them.

How These Questions Work

Logical reasoning questions that ask you how to best support or damage an argument are some of the easiest to answer. You probably analyze ideas every day and think of evidence to attack or defend those ideas. Because you already have the skill to evaluate arguments, it doesn't take much work for you to modify that skill to fit this specific LSAT question format. This question category has two subtypes: One asks you to strengthen an argument, and the other asks you to weaken it. You'll recognize these questions because they include words that mean to strengthen or weaken (like support, bolster, or impair), and they almost always contain an “if true” qualifier.

 Nearly all these questions contain the words “if true,” but not all questions that have “if true” in them are strengthening-or-weakening-the-argument types. To make sure an “if true” question is really a strengthening-or-weakening question, look for the identifying language that asks you to either strengthen or weaken the argument.

Here are three simple steps to follow when approaching strengthening-or-weakening-the-argument questions:

1.     Read the question very carefully so you know exactly what it is you're strengthening or weakening.

In most cases, it's the main argument's reasoning. But in less frequent cases, you may be asked to support or impair a different line of reasoning, like the view of the author's opponent.

2.     Examine the argument to find the premises and conclusion and to determine what method of reasoning the author uses to reach the conclusion.

Usually the author uses inductive reasoning, so you need to figure out whether the argument relies on analogy, statistics, or cause and effect to arrive at the conclusion. In the upcoming sections, we tell you what to look for in each type of reasoning.

3.     Evaluate the answer choices to determine which choice best fits with the author's conclusion and method of reasoning.

Assume all the answer choices are true and then determine which one best either supports or undermines the specific line of reasoning addressed in the question.

 Always assume that all the answers to strengthening-or-weakening-the-argument questions are true. Almost all these questions include the words “if true” in them to remind you that you're supposed to assume that each answer choice presents a true statement. Don't fall into the trap of trying to evaluate whether answer choices are true or false! Your only job is to determine whether the choices help or hurt the argument. This means that a statement like “humans do not breathe air” could be a correct answer choice even though you know it's not true. Perhaps you're supposed to weaken an argument that concludes that a company must pump air into an underwater habitat for humans. If humans don't breathe air, pumping in air may not be necessary. Make sure you don't dismiss any answer choices simply because you know or suspect they aren't true in the real world.

Affecting cause-and-effect arguments

Questions that ask you to evaluate arguments often feature cause-and-effect reasoning. If the argument uses cause and effect to make its point, focus on the causes. Almost always, the right answer to a question that asks you to strengthen the argument shows that the cause mentioned is the most likely source of the effect. The best answer for a question for which you have to weaken the argument points to another probable cause of the effect. Here's how you apply this reasoning to a sample question:

 Average hours of television viewing per American have sharply increased for more than three decades. Over the same period of time, there has been an increase in obesity rates in America. To fight the rise in obesity, Americans must limit their hours of television viewing.

Which one of the following, if true, would most weaken the author's argument?

(A) A person burns more calories while watching television than while sleeping.

(B) Over the last 30 years, there has been an increase in the number of fast food restaurants in the United States.

(C) Americans spend most of their television time watching sports events rather than cooking shows.

(D) Television viewing in Japan has also increased over the past three decades.

(E) Studies show that the number of television commercials that promote junk food has risen over the past ten years.

To tackle this question, first identify the conclusion and the premises the author states or implies to reach that conclusion. The conclusion is pretty easy to spot. The last thought of the argument is that Americans must limit their hours of TV viewing to curb the rise in obesity. The author makes this judgment using the following evidence:

·        The author directly states that the number of TV viewing hours has increased over the last 30 years.

·        According to the author, the number of obese Americans has also increased.

·        The author implies that TV viewing causes obesity.

To weaken the argument that Americans have to reduce their TV watching, you have to find the answer choice that shows that there could be another cause for the rise in obesity.

You may have been tempted to select Choice (A) because it shows that TV watching may be less fat-producing than another activity, sleeping. But it doesn't give you another reason for the rise in obesity. Choice (A) could be right only if it showed that Americans are sleeping more than they were 30 years ago. It doesn't, so move on.

On the other hand, stating that during the same time period the number of fast food restaurants also increased introduces another possible cause of obesity and weakens the conclusion that Americans have to stop watching so much TV to get slimmer. Maybe it's the popularity of fast food that's the culprit! Choice (B) is a better answer than Choice (A), but read through all the possibilities before you commit. Choice (C) is wrong because the argument contains nothing that suggests that the type of TV Americans watch affects their obesity, nor does Choice (C) show that viewing patterns have changed over the last three decades. You can eliminate Choice (C) from contention. And Choice (D) is also out because it doesn't correlate what's happening in Japan with what's happening in the United States. You don't know whether Japanese citizens weigh more now than they did 30 years ago, so the information in Choice (D) is useless.

If the question had asked you to strengthen the conclusion, Choice (E) would be a good option. It shows a reason that increased TV watching could cause obesity. But the question asks you to weaken the conclusion, so Choice (B) is the best answer. It's the only one that shows that there could be another cause for the rise in obesity.

Analyzing analogy arguments

Remember that analogy arguments rely on the similarity of the two persons, things, or ideas being compared. Therefore, if the author uses an analogy to reach a conclusion, answer choices that show similarities between the compared elements support the conclusion, and choices that emphasize the differences between the elements weaken the conclusion. Take a look at this example of an analogy argument:

 Hundo is a Japanese car company, and Hundos run for many miles on a gallon of gas. Toyo is also a Japanese car company; therefore, Toyos should get good gas mileage, too.

The author's argument would be best supported by which one of the following, if that statement were true?

(A) All Japanese car manufacturers use the same types of engines in their cars.

(B) British cars run for as many miles on a tank of gas as Hundos do.

(C) The Toyo manufacturer focuses on producing large utility vehicles.

(D) Toyo has been manufacturing cars for more than 20 years.

(E) All Japanese cars have excellent service records.

Recognizing the premises and conclusion in this argument is simple. The author states directly that Hundo cars are Japanese and get good gas mileage and that Toyo cars are Japanese; therefore, Toyos also get good gas mileage. Your job is to find the answer that bolsters the similarity between Hundos and Toyos.

 You can generally eliminate answer choices that introduce irrelevant information, such as Choices (B), (D), and (E). The author compares Japanese cars, so British cars have nothing to do with the argument. The length of time that Toyo has been in business tells you nothing about how similar its cars are to Hundo's. And the question is talking about gas mileage, not service records, so don't spend too much time considering Choice (E).

Choice (C) tells you the focus of Toyo producers, but it doesn't give you any information about how that compares to Hundo, so the best answer is Choice (A). If all Japanese manufacturers supply their cars with the same engines, and Hundo and Toyo are both Japanese manufacturers, it's more likely that Toyos will achieve a gas mileage similar to that experienced by Hundos.

Stabbing at statistical arguments

If you see statistics used to promote an argument, look for an answer that shows whether the statistics actually relate to the conclusion's topic. If they do, you'll strengthen the conclusion. On the other hand, an answer that shows the statistic is unrelated to the conclusion significantly weakens that conclusion. The following is an example of a statistical logical reasoning question you could find on the LSAT:

 In a survey of 100 pet owners, 80 percent said that they would buy a more expensive pet food if it contained vitamin supplements. Consequently, CatCo's new premium cat food should be a top seller.

Which one of the following, if true, would most weaken the author's argument?

(A) Some brands of cat food contain more vitamin supplements than CatCo's does.

(B) CatCo sells more cat food than any of its competitors.

(C) Some of the cat owners surveyed stated that they never buy expensive brands of cat food.

(D) Ninety-five of those pet owners surveyed did not own cats.

(E) Many veterinarians have stated that vitamin supplements in cat food do not greatly increase health benefits.

Because the argument hinges on statistics, eliminate answers that don't directly address the statistical evidence. Those surveyed stated they would pay more for pet food with vitamin supplements, but they didn't provide information on whether the amount of vitamin supplements was important. So even though Choice (A) may entice you, it isn't the best answer because it doesn't address the statistics used in the argument. Choice (B) doesn't regard the survey results either, and it seems to support the conclusion rather than weaken it. The argument has nothing at all to do with veterinarians, so Choice (E) can't be right. Only Choice (C) and Choice (D) deal with the survey the author uses to reach the conclusion that CatCo's premium cat food will be a big seller.

 You can eliminate answer choices that show there's an exception to the statistical evidence. Exceptions don't significantly weaken a statistical argument.

Therefore, Choice (C) is wrong and Choice (D) is the best answer because it demonstrates a weakness in the statistics the author uses to support the conclusion. The preferences of dog or bird owners wouldn't be a good indicator of the habits of cat owners.

 Strengthen/weaken questions lend themselves quite well to the technique of trying to answer the question before reading the answers. If you can identify the conclusion, take a moment to think about how you'd answer the question if you didn't have an array of answers to choose from. Consider what the author is claiming, and then consider how you'd strengthen it, weaken it, or whatever the question wants you to do.

Build It Up: Strengthen/Support Questions

Sometimes lawyers want to bolster their arguments. They look for evidence, court decisions, and laws that support the claims they're making. Spotting evidence that can support an argument is a real skill; law schools teach it, but they want their students to arrive already understanding the basic concept. That's why the LSAT includes logical reasoning on the test.

The logical reasoning section includes some questions that ask you to pick answers that can strengthen the argument. The questions may use the word strengthen, but they may also ask you to support a position or justify reasoning. No matter how they're phrased, they're all asking you to do the same thing — to spot the answer that can make the argument's conclusion more likely.

Check out some examples of strengthen/support questions:

·        Which one of the following, if true, most strengthens the argument?

·        Which one of the following, if true, most strongly supports the statement above?

·        Which one of the following, if true, would provide the most support for the teacher's assertion?

·        Which one of the following, if true, most helps to support the position of the second group of economists?

·        Which one of the following discoveries, if it were made, would most support the hypothesis stated above?

·        Which one of the following, if true, most supports Martin's counter to Jessica?

·        Which one of the following principles, if valid, most helps to justify the reasoning above?

·        Which one of the following principles, if established, most helps to justify Susan's position?

·        Which one of the following principles, if valid, most helps to justify the bookstore owner's argumentation?

·        Which one of the following principles, if valid, most justifies the physicist's conclusion?

 The approach to answering all these strengthen/support questions is the same: Figure out what the conclusion is and what the premises are, and then figure out what would make the connection between them stronger and more believable. Try to come up with your own answer before you consider the choices.

Tear It Down: Weakening Questions

Almost as important as strengthening your own arguments is tearing down your opponent's. Lawyers spend at least as much time attacking their opponent's arguments as they do bolstering their own. No matter how strong your case is, your opponent will have a tough case in response. Even if the opposing case is flimsy as gauze, you still have to go through the necessary steps of taking it apart. That's why the LSAT tests for this skill.

The logical reasoning section contains several questions asking you to weaken an argument. These questions may use the word weaken. They also may ask you to criticize, undermine, or attack the argument.

Here are some weaken questions:

·        Which one of the following, if true, most weakens the argument?

·        Which one of the following, if true, most seriously weakens the argument?

·        Which one of the following statements, if true, most seriously weakens the argument above?

·        Which one of the following, if true, most undermines the doctor's argument?

·        Which one of the following, if true, most undermines George's objection to Marisol's analysis?

The approach to these questions is exactly like the approach to strengthen/support questions, except that you want to hurt the argument, not help it. Find the conclusion, figure out what evidence and reasoning the author used to get there, and come up with something that makes the relevance of that evidence to that conclusion seem less likely.

A Twist: EXCEPT Questions

Many strengthen/weaken questions don't ask for the choice that best strengthens (or weakens, or supports, or undermines) the argument but instead for the one choice that doesn't do one of those things. These questions end in the extremely important word EXCEPT. It's always capitalized, so you can't miss it.

These questions look like this:

·        Each of the following, if true, supports the argument above EXCEPT:

·        Each of the following, if true, would weaken the commentator's argument EXCEPT:

·        Each of the following, if true, supports the physicist's hypothesis EXCEPT:

·        Each of the following, if true, weakens the argument EXCEPT:

·        Each of the following, if true, strengthens the argument EXCEPT:

They can also look like this:

·        Which one of the following, if all of them are true, is LEAST helpful in establishing that the conclusion above is properly drawn?

·        Which one of the following, if all of them are true, is LEAST effective at undermining the politician's argument?

They're still strengthen/weaken questions, but instead of finding one answer to strengthen/weaken/support/undermine, you want to find four.

 As always, first read the question carefully. These questions aren't your standard strengthen/weaken questions. Instead, they offer four choices that do strengthen or weaken the conclusion, and one that doesn't. You don't necessarily have to find an answer that strengthens or weakens the conclusion; you just want an answer that doesn't do what the other four do. For example, if the question reads “Each of the following, if true, weakens the argument EXCEPT:” the correct answer doesn't necessarily strengthen the argument, but it definitely doesn't weaken it.

Here's an example of a question that has four answers that weaken the argument and one that doesn't:

 Some workers in microwave popcorn factories have contracted a rare lung disease. Experts have linked this disease to a chemical used in the process of mixing popcorn and flavorings. Consumers should, therefore, stop buying and eating all types of microwave popcorn to avoid the risk of contracting this lung disease.

Each of the following, if true, weakens the argument EXCEPT:

(A) The lung disease is caused by being exposed to the chemical for many hours at a time over a period of years.

(B) The chemical only becomes toxic when it is held at a temperature much higher than that reached by popcorn in a microwave.

(C) The lung disease has only been found in workers who handled the Cajun Spice flavor of popcorn.

(D) In 20 years of widespread microwave popcorn consumption, no consumer has ever contracted this rare lung disease.

(E) The EPA has not yet done any research to determine whether the chemical that causes the lung disease is present in the steam and air that come out of a bag of popcorn when it is opened.

From reading the question first, you know you want an answer that doesn't weaken the argument. The conclusion is that consumers should stop eating all types of microwave popcorn to avoid catching a disease. The evidence for this conclusion is that a chemical in microwave popcorn caused this disease in popcorn factory employees.

What weakens the argument? Any evidence that makes consumers seem safe. If you can prove that the disease is somehow restricted to the factory workers, you can reassure consumers that they can eat microwave popcorn with impunity. What doesn't weaken the conclusion? Any evidence indicating that consumers can catch the disease from eating microwave popcorn, or any evidence that's of unclear relevance or simply off-topic.

·        Choice (A) weakens the argument because most consumers aren't exposed to the chemical in question for long periods of time.

·        Choice (B) weakens the argument because consumers aren't keeping their popcorn hot enough.

·        Choice (C) weakens the suggestion that consumers should avoid all kinds of microwave popcorn, though possibly not the suggestion that they should avoid Cajun Spice flavor.

·        Choice (D) weakens the suggestion because it makes the risk to consumers appear almost negligible.

·        Choice (E) doesn't weaken the argument; if the EPA hasn't yet done any research into the chemical's presence in popcorn steam, then the chemical could well be lurking in there, ready to sicken hapless consumers.

Choice (E) doesn't especially strengthen the argument, but it doesn't weaken it, either. Choice (E) is the correct answer.