Chapter 8

Conclusions, Inferences, Assumptions, and Flaws in Logical Reasoning Questions

IN THIS CHAPTER

check Identifying and practicing conclusion questions

check Tapping into inductive reasoning to tackle inference questions

check Approaching seeking-assumptions questions

check Rooting out logical flaws

Logical reasoning questions come in various types, which require you to focus on different aspects of each argument. The most basic task involved in logical reasoning questions is identifying the argument’s conclusion. To answer most questions, you first have to spot the conclusion and then figure out how and why the author reached that conclusion. For some questions, though, all you have to do is identify the conclusion. Look at those questions as a gift. Other logical reasoning questions are a bit more complicated; you must not only spot the conclusion but also figure out how the author uses evidence to support the conclusion, either effectively or not so effectively.

In this chapter, you discover how to approach questions that ask you to spot a conclusion and figure out how the author reached that conclusion, or questions that ask you to draw a conclusion from a set of premises. The most basic conclusion-type questions simply require you to spot the conclusion or draw your own. The more complicated assumption and logical flaw questions ask a bit more of you; you first have to spot the conclusion, and then you figure out what facts the author assumed to reach that conclusion or point out a mistake the author made in applying the evidence.

Jumping to Logical Conclusions

The LSAT tests your ability to identify conclusions in two ways. One type presents a full argument with premises and a conclusion and then asks you to identify the statement that constitutes the conclusion. These questions are relatively easy. Classify each statement in the argument as either one that leads to a conclusion or one that contains the ultimate opinion that results from the other statements. This type of question may be worded like these:

Which one of the following most accurately expresses the main conclusion of the argument?
Which one of the following most accurately expresses the conclusion drawn in the paragraph?

More frequently, the LSAT tests your ability to draw logical conclusions (or hypotheses) from a series of premises (the evidence). You choose an answer that best concludes the information. Questions that ask you to draw conclusions from premises may be worded like this:

Which one of the following is most strongly supported by the information above?
If the statements above are true, which one of the following is most strongly supported on the basis of them?
Which one of the following most logically completes the argument?

As you read through the premises, think of a logical conclusion of your own. Then look through the answer choices to see whether one comes close to matching what you’ve thought up.

The key to correctly answering these more common conclusion questions is to look for the answer choice that addresses most of the information contained in the premises. Eliminate any choices that are off-topic or incomplete. A conclusion that addresses only part of the information may be plausible, but it probably isn’t the best answer. For example, consider the following premises:

Five hundred healthy adults were allowed to sleep no more than five hours a night for one month. Half of the group members were allowed 90-minute naps in the afternoon each day; the remaining subjects were allowed no naps. Throughout the month, the subjects of the experiment were tested to determine the impact of sleep deprivation on their performance of standard tasks. By the end of the month, the group that was not allowed to nap suffered significant declines in performance, while the napping group suffered more moderate declines.

The best conclusion for these premises would have to address the following:

The nightly sleep deprivation of healthy adults
The allowance for naps for half of the study group
The smaller decline in performance of standard tasks for the group that took naps

Any conclusion that fails to address all three points isn’t the best conclusion. For example, the statement “Sleep deprivation causes accumulating declines in performance among healthy adults” wouldn’t be the best conclusion because it fails to address the effect of naps. A better conclusion would be, “Napping helps reduce the declines in performance caused by nightly sleep deprivation among healthy adults.”

You’ll often see more than one plausible conclusion among the answer choices. Your task is to identify the best choice. Don’t fall for the trap of choosing an answer that just restates one of the premises. Answer choices that restate a premise may entice you because they echo part of the information in the argument, but the best choice must contain an element of each of the pieces of information presented in the question.

The process is pretty simple, really. Try this sample question to see for yourself:

Over the last eight years, the Federal Reserve Bank has raised the prime interest rate by a quarter-point more than ten times. The Bank raises rates when its Board of Governors fears inflation and lowers rates when the economy is slowing down.

Which one of the following is the most logical conclusion for this paragraph?

(A) The Federal Reserve should be replaced with regional banks that can respond more quickly to changing economic conditions.

(B) The Federal Reserve has raised the prime rate in recent years to try to control inflation.

(D) The monetary policy of the United States is no longer controlled by the Federal Reserve.

(E) The Federal Reserve has consistently raised the prime rate over the last several years.

You know from the language that this is a conclusion question, so you don’t have to look for a conclusion in the argument. Just read through the premises and formulate a quick conclusion, something like, “Because the Federal Reserve has raised interest rates many times over the last eight years, it must fear inflation.”

Eliminate answer choices that aren’t relevant or that contain information not presented by the premises. The paragraph says nothing about regional banks or the termination of the Federal Reserve’s control over U.S. monetary policy, so you can disregard Choices (A) and (D). Then get rid of any choices that don’t take all premises into consideration. Choice (E) just reiterates the first premise, so it’s wrong. You’re left with Choices (B) and (C), but Choice (C) contradicts the information in the premises. The problem says the Federal Reserve responds to the economy, not the other way around, so it would be wrong to say the Federal Reserve causes a recession. Choice (B) is clearly the best answer. It takes into consideration the information that the Federal Reserve has raised rates and that raising rates is its response to inflation.

Warning Be careful to avoid relying on outside knowledge or opinions when answering conclusion questions. You may have studied the Federal Reserve Bank and have opinions about monetary policy. Choices (A), (C), and (D) reflect some possible opinions about the Federal Reserve. Don’t get trapped into choosing an answer just because it supports your opinion.

Using Your Noggin to Make Inferences

Logical reasoning inference questions ask you to make an inference from a series of statements. These questions may contain the word infer, but more often they ask you to choose the answer that is most strongly supported by the statements. So you may make inferences for questions worded like these:

Which of the following can be properly inferred from the statements above?
If the statement above are true, then which one of the following must also be true?
Which one of the following is most strongly supported by the consumer’s statements?
The information above provides the most support for which one of the following statements?

The key to answering these questions correctly is to remember that they usually ask you to make an inference based on information in the paragraph’s statements rather than draw an overall conclusion based on all of them. So you should choose an answer that makes a plausible inference about or connection between one or more of the statements. Like the correct answer choices for the conclusion questions, the best answers to this type of question don’t go beyond the scope of the information provided in the passage. So eliminate answer choices that concern information not specifically addressed by at least one of the statements.

Television ratings are based on the number of overall viewers, but the highest-rated television shows do not always command the most advertising dollars. Many advertisers are willing to pay more for spots that run during shows that attract a high proportion of males between the ages of 19 and 34 than for ads that run during other, more highly rated shows that do not attract as large a proportion of males aged 19 to 34. Ads that run during televised sporting events are often more expensive than ads that run during other types of programs.

Which one of the following is most strongly supported by these statements?

(A) Advertisers have done little research into the typical consumer and are not using their advertising dollars wisely.

(B) Sports programs are viewed by a greater proportion of males aged 19 to 34 than are other prime-time network programs.

(C) The ability to reach a particular demographic is more important to many advertisers than reaching the greatest number of overall viewers.

(D) Many advertising executives prefer sports programs and assume that other Americans do as well.

(E) Ads that run during the most popular sporting events are the most expensive of all ads.

You know you’re dealing with an inference question because the question asks for the most strongly supported answer based on the statements. Focus on the paragraph’s statements as you read. Then look through the answer choices and eliminate any that don’t address or connect the statements.

The statements say nothing about advertising research and don’t make value judgments about particular advertising practices, so you can eliminate Choice (A) immediately. Likewise, Choice (D) mentions the program preferences of advertisers, but none of the statements concerns what advertisers like to watch, so you can get rid of Choice (D). Choice (E) is wrong because the statements don’t support an inference about what would constitute the most expensive ads. Just because sporting events ads are “often more expensive” than other ads doesn’t necessarily mean that they’re always the most expensive. This leaves you with Choices (B) and (C).

The author implies that some televised sporting events have lower overall ratings, even though they have higher advertising rates. Plus, the statements don’t indicate who watches televised sporting events. So you can’t justify Choice (B). You’re left with Choice (C), which provides an explanation for the information in the second sentence that states that advertisers are more willing to pay more for lower-rated shows that are nevertheless viewed by a larger proportion of males between 19 and 34. This practice makes sense if the advertisers are trying to attract young male consumers. Choice (C) is best.

Warning Remember to check your outside knowledge about the subjects at the door! You may know that Super Bowl ads are the most expensive ads, which may tempt you to pick Choice (E). Using your own knowledge rather than what’s expressly stated in the test questions will cause you to miss questions that someone with less knowledge may answer correctly.

Making Assumptions

Making an argument without assuming at least one or two points is nearly impossible. If you back up everything you say, it can take forever, and sometimes you have to assume something just for the sake of argument. Assumptions aren’t necessarily bad, but you do need to recognize them when they occur.

Seeking-assumptions questions ask you to identify a premise that isn’t present in the argument. For these types of questions, the author directly states a series of premises and provides a clear conclusion, but in getting to that conclusion, the author assumes information. Your job is to figure out what the author assumes to be true but doesn’t state directly in drawing the conclusion.

For example, if the argument says, “My house is full of bees, so I need to call an exterminator,” you know the author must assume that the exterminator can do something about the bees, even though the argument doesn’t explicitly state this fact.

Seeking-assumptions questions may look like these:

Which one of the following is an assumption required by the argument above?
The professor’s conclusion follows logically if which one of the following is assumed?
Which one of the following is an assumption on which the scholar’s reasoning depends?
The politician’s argument depends on assuming which one of the following?
On which one of the following assumptions does the argument rely?
Which one of the following, if assumed, would allow the conclusion to be properly drawn?
Which one of the following, if assumed, enables the argument’s conclusion to be properly inferred?
The argument requires the assumption that …

Words like assume, rely, presume, depend on, and their derivatives usually indicate seeking-assumptions questions. Remember, these questions ask you to look for the ideas the author relies on but doesn’t state.

As you read seeking-assumptions questions, look for information that’s necessary to the argument but isn’t stated by the author. In these questions, the author always takes for granted something on which the entire argument depends. You just need to identify what that is. To do so effectively, choose an answer that links the existing premises to the conclusion. The assumption you’re seeking always bears directly on the conclusion and ties in with one or more premises, often with the last premise. Therefore, the best answer often contains information from both the last premise and the conclusion. Try on this one for size:

Women receive fewer speeding tickets than men do. Women also have lower car insurance rates. It is clear that women are better drivers than men.

On which of the following is an assumption on which the conclusion relies?

(A) Men drive cars more frequently than women do.

(B) The percentage of female drivers in the population is greater than the percentage of male drivers.

(D) Most men prefer sports cars to sedans.

(E) Having lower car insurance rates indicates that one is a better driver than those who have higher rates.

As always, read the question first. Because it references assumptions, we bet you figured out pretty quickly that it’s a seeking-assumptions question.

Next, read through the argument and try to figure out the assumption or assumptions the author makes in reaching the conclusion that women are better drivers. The author moves from the premises to the conclusion pretty quickly and assumes that fewer speeding tickets and lower car insurance rates indicate better driving skills. The author also assumes that men and women have equal driving experiences because the evidence is about the number of ticketed men and women, not the percent of ticketed men and women (if women just drove less than men, then they could easily have fewer tickets without actually being better drivers). Use this information to examine each of your options.

The author uses the premise that women have lower insurance rates to support the conclusion that women are better drivers, so the author must assume that better drivers enjoy lower insurance rates, so the answer must be Choice (E). Choice (A) may provide an explanation for why more men receive speeding tickets, but it doesn’t lead to the conclusion that women are better drivers. Choice (B) is wrong. The conclusion may presume that the number of men and women drivers is equal, but the conclusion that women are better drivers than men doesn’t rely on the assumption that there are more women drivers. Choice (C) is irrelevant to an argument that uses number of speeding tickets to reach its conclusion, and Choice (D)’s reference to sports cars is completely off base.

Often, the correct answer to an assumption question is the one that links one of the premises directly to the conclusion.

Finding Flaws in an Argument

Not every argument is convincing. In fact, many (if not most) arguments have something wrong with them. As a lawyer, you have to spot your opponents’ bad arguments so you can attack them and spot bad arguments in your own work so you can fix them. Many logical reasoning questions have flaws. The LSAT-makers place the flaws there to test your ability to spot them.

These problems are a bit more complicated than questions that simply ask you to draw a conclusion. First you find the conclusion, then you figure out how the author reached it, and finally you determine what’s wrong with that reasoning process.

Take a look at some examples of spot-the-flaw questions:

Which one of the following most accurately describes a flaw in the argument?
The reasoning above is flawed because it fails to recognize that …
The argument is vulnerable to criticism on which one of the following grounds?
The reasoning in the argument is flawed because the argument fails to take into account that …
The argument is questionable because it fails to consider …

Occasionally, the LSAT asks you to find the flaw in a formal argument. Usually the author draws a faulty conclusion by confusing a sufficient condition with a necessary one. For example, an argument may fallaciously conclude that because only girls wear pink and Jane is a girl, Jane must be wearing pink. Notice that if the first premise stated that all girls wear pink, the conclusion that Jane is wearing pink would be justified. The majority of finding-the-flaw questions, however, concern informal arguments and are easier to answer when you’re familiar with informal fallacies. Some of the informal fallacies most commonly tested on the LSAT are these:

Fallacies of relevance occur when the conclusion isn’t relevant to the premises offered to support it.
- An appeal to force specifies that you better believe a conclusion is true or you’ll suffer harm.
- The bandwagon approach requires you to accept a conclusion because everybody else does.
- The red herring introduces a premise that has nothing to do with the argument and then bases the conclusion on that irrelevant point.
- An ad hominem attack opposes another’s argument by attacking the person rather than the conclusion’s reasonability.
Fallacies of weak induction occur when the premises don’t adequately support the conclusion.
- An appeal to authority is fallacious when the authority used to support a claim isn’t an expert in the argument’s subject.
- A hasty generalization occurs when the sample size provided to support a claim is inadequate.
Fallacies of ambiguity use unclear or undefined meanings.
Fallacies of presumption occur when someone’s claim presumes an unsubstantiated truth.
- Circular reasoning occurs when the premise used to support a conclusion is the conclusion itself.
- A complex question is a question presented in such a way that you can’t answer it without implicating yourself.
- A false dichotomy occurs when an argument provides only two options, provides evidence to reject one of those options, and then concludes that the other option is the only viable truth without recognizing that other options exist.
Fallacies of analogy result from comparing entities that aren’t sufficiently similar to warrant a comparison. They may also occur when one claims that because the parts of a whole are a certain way, the whole is also that way, or because a whole is a certain way, the parts individually are also that way.

Watch for these informal fallacies when you approach a question that asks you to find the flaw, such as the following example.

Some southern towns have quaint downtown areas, and some southern towns have small colleges. Therefore, some southern towns with small colleges also have quaint downtown areas.

The reasoning in the argument is flawed because the argument

(A) implies a definite causal relationship from a coincidence that could be explained in other ways.

(B) contains a premise that cannot be true unless the conclusion is known to be true.

(D) fails to acknowledge that one group could have members in common with each of two other groups without those other two groups sharing any members in common.

(E) mistakes towns that have quaint downtown areas for towns that have small colleges.

As always, your first step is to read the question. It asks you to figure out what’s wrong with the argument’s reasoning. Now read the argument. It concludes that because some southern towns have quaint downtowns and some have small colleges, some have both. This sounds like a fallacy of analogy. The problem with the argument’s conclusion is that it assumes overlap between two sets (“southern towns with quaint downtown areas” and “southern towns with small colleges”) that don’t necessarily have to overlap. It’s entirely possible that the two sets of towns aren’t similar at all and that no town has both a quaint downtown and a small college.

Now read through the answers, looking for a choice that suggests a problem with the analogy. Choice (A) is wrong because no causal relationship is implied. Choice (B) is wrong because no premise of the argument depends on the conclusion; in other words, the first statement can stand on its own without the conclusion. Choice (C) is wrong because the word “quaint” is used the same way both times to describe downtown areas. Choice (D) looks correct; the argument does illogically suppose that because one group (southern towns) has members in common with two other groups (towns with quaint downtown areas and towns with small colleges), those two latter groups must also share members. Choice (E) is wrong because the argument doesn't confuse the two types of towns with each other; it keeps them distinct while reaching the erroneous conclusion. Choice (D) is the best answer.

If the argument had used the word most instead of some, you could assume overlap. The statement “Most southern towns have quaint downtowns, and most southern towns have small colleges; therefore, some southern towns have both” would be perfectly acceptable.