Section Types Logical Reasoning

LSAT 35 - Section 4 - Question 11

July 15, 2015

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LSAT 35 - Section 4 - Question 13

July 15, 2015

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LSAT 111 - Section 4 - Question 11

July 15, 2015

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LSAT 111 - Section 4 - Question 13

July 15, 2015

Mayor: The law prohibiting pedestrians from crossing against red lights serves no useful purpose. After all, in order to serve a useful purpose, a law must deter the kind of behavior it prohibits. But pedestrians who invariably violate this law are clearly not dissuaded by it; and those who comply with the law do not need it, since they would never cross against red lights even if there were no law prohibiting pedestrians from crossing against red lights.

Summarize Argument

The mayor concludes that the law prohibiting pedestrians from crossing against red lights is useless. He supports this with three premises:

(1) To be useful, a law must prevent the behavior that it bans.

(2) Pedestrians who always break this law are not dissuaded by it.

(3) Pedestrians who always follow the law don’t need it, because they wouldn’t cross on red even without the law.

Identify and Describe Flaw

This is the cookie-cutter flaw of “false dichotomy,” where the author falsely divides the world into two binary halves. In this case, the mayor divides the world into pedestrians who always break this law and pedestrians who never break it. He doesn’t consider that there might be other people who only sometimes break this law; how might the law affect them?

A

takes for granted that most automobile drivers will obey the law that prohibits them from driving through red lights

The mayor only addresses pedestrians and the law that prohibits them from crossing against red lights. Whether drivers obey the law that prohibits them from driving through red lights is irrelevant.

B

uses the word “law” in one sense in the premises and in another sense in the conclusion

This is the cookie-cutter flaw of “equivocation.” The mayor doesn’t make this mistake because he uses the word “law” consistently throughout his argument.

C

ignores the possibility that a law might not serve a useful purpose even if it does deter the kind of behavior it prohibits

This may be true, but it isn’t a flaw in the mayor’s argument. He just claims that a law is only useful if it does deter the kind of behavior it prohibits.

D

fails to consider whether the law ever dissuades people who sometimes but not always cross against red lights

The mayor falsely divides the world into people who always cross against red lights and people who never cross against red lights. He doesn’t consider people who sometimes cross against red lights or how the law might affect them.

E

provides no evidence that crossing against red lights is more dangerous than crossing on green lights

It’s true that the major never provides evidence about the danger of crossing on red or green lights, but this isn’t a flaw because his argument is only about crossing against red lights. So (E) is irrelevant.

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LSAT 35 - Section 4 - Question 08

July 15, 2015

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LSAT 111 - Section 4 - Question 08

July 15, 2015

It is widely believed that by age 80, perception and memory are each significantly reduced from their functioning levels at age 30. However, a recent study showed no difference in the abilities of 80-year-olds and 30-year-olds to play a card game devised to test perception and memory. Therefore, the belief that perception and memory are significantly reduced by age 80 is false.

Summarize Argument: Counter-Position

The author concludes that the belief that perception and memory are significantly reduced by age 80 is false. She supports this with a recent study showing no difference in the abilities of 80-year-olds and 30-year-olds to play a card game that tests perception and memory.

Identify and Describe Flaw

The author assumes that perception and memory aren't greatly reduced by age 80 simply because 80-year-olds performed just as well as 30-year-olds on the card game. However, she doesn't consider that the game might only test basic levels of perception and memory. If the game requires only a low level of these abilities, the author can't conclude that perception and memory aren't reduced by age 80.

A

the study’s card game does not test cognitive abilities other than perception and memory

This doesn’t impact the argument, so failing to consider it can’t be a flaw. Because the argument only addresses perception and memory, whether the card game tests other cognitive abilities is irrelevant.

B

card games are among the most difficult cognitive tasks one can attempt to perform

We don’t know if this general statement about card games applies to the particular card game designed to test perception and memory. But even if it does, (B) might strengthen the argument by suggesting that 80-year-olds are just as good as 30-year-olds at such a difficult task.

C

perception and memory are interrelated in ways of which we are not currently aware

This doesn’t impact the argument, so failing to consider it can’t be a flaw. The card game showed similar levels of perception and memory between 80-year-olds and 30-year-olds. Whether perception and memory are connected in unknown ways doesn’t affect this outcome.

D

the belief that 80-year-olds’ perception and memory are reduced results from prejudice against senior citizens

Even if this is true, it doesn't point out a flaw in the author’s argument because she’s trying to disprove this belief.

E

playing the study’s card game perfectly requires fairly low levels of perception and memory

The author fails to consider the possibility that the game might only test basic levels of perception and memory. If this is true, then the game would reveal very little about the levels of perception and memory in 80-year-olds vs. in 30-year-olds.

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LSAT 35 - Section 4 - Question 07

July 15, 2015

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LSAT 111 - Section 4 - Question 07

July 15, 2015

Attorney: I ask you to find Mr. Smith guilty of assaulting Mr. Jackson. Regrettably, there were no eyewitnesses to the crime, but Mr. Smith has a violent character: Ms. Lopez testified earlier that Mr. Smith, shouting loudly, had threatened her. Smith never refuted this testimony.

Summarize Argument

The attorney concludes that Mr. Smith should be found guilty of assaulting Mr. Jackson. She supports this by saying that Ms. Lopez testified that Mr. Smith loudly threatened her and he never refuted her testimony, so Mr. Smith has a violent character.

Identify and Describe Flaw

The attorney makes many unwarranted assumptions in her argument. She assumes that just because Smith loudly threatened Lopez, he must have a violent character, and that just because he has a violent character, he’s guilty of assaulting Jackson.

She also assumes that just because Smith never refuted Lopez’s claim that he threatened her, her claim must be true.

Note the questions stem: “The attorney’s argument is fallacious because it reasons that ____.” The correct answer will fill in this blank with an assumption made by the attorney.

A

aggressive behavior is not a sure indicator of a violent character

The attorney does not reason that aggressive behavior is not a sure indicator of a violent character. Instead, she assumes that Smith’s aggressive behavior (his alleged loud threat) is a sure indicator of his violent character.

B

Smith’s testimony is unreliable since he is loud and aggressive

The attorney doesn’t bring up any of Smith’s testimony at all, nor does she assume that it’s unreliable.

C

since Smith never disproved the claim that he threatened Lopez, he did in fact threaten her

This points out one of the attorney’s fallacious assumptions. She assumes that, because Smith didn’t refute Lopez’s claim, her claim must be true. She uses this to argue that Smith has a violent character and thus committed the crime.

D

Lopez’s testimony is reliable since she is neither loud nor aggressive

The attorney supports Lopez’s testimony by saying that it was never refuted. She doesn’t assume that Lopez’s testimony is reliable because Lopez isn’t loud or aggressive.

E

having a violent character is not necessarily associated with the commission of violent crimes

The question stem asks for an answer in terms of what the argument reasons. In contrast to (E), “the attorney’s argument is fallacious because it reasons that” having a violent character is necessarily associated with the commission of violent crimes.

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LSAT 35 - Section 4 - Question 05

July 15, 2015

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LSAT 111 - Section 4 - Question 05

July 15, 2015

One of the advantages of Bacillus thuringiensis (B.t.) toxins over chemical insecticides results from their specificity for pest insects. The toxins have no known detrimental effects on mammals or birds. In addition, the limited range of activity of the toxins toward insects means that often a particular toxin will kill pest species but not affect insects that prey upon the species. This advantage makes B.t. toxins preferable to chemical insecticides for use as components of insect pest management programs.

Summarize Argument

The author concludes that B.t. toxins are better for managing insect pests than chemical insecticides. Why? Because particular B.t. toxins will kill only particular species, leaving other insects, birds, and mammals unharmed.

Notable Assumptions

The author assumes that chemical pesticides do not target particular species effectively in the same way as B.t. toxins. She assumes there is no other property of B.t. toxins that makes them less effective or more risky than chemical insecticides in practice.

A

Chemical insecticides cause harm to a greater number of insect species than do B.t. toxins.

This is irrelevant without knowing whether the species harmed are common pests. If B.t. toxins cause damage only to pest insects, but chemical insecticides cause damage to harmless insects, then the argument is strengthened.

B

No particular B.t. toxin is effective against all insects.

This doesn’t mean there is any insect for which no B.t. toxin is effective. It’s possible that every pest insect can be targeted with the appropriate B.t. toxin.

C

B.t. toxins do not harm weeds that do damage to farm crops.

This is irrelevant without information about whether chemical insecticides do the same. If neither substance does damage to such weeds, this offers no contrast.

D

Insects build up resistance more readily to B.t. toxins than to chemical insecticides.

This is a reason why B.t. toxins may be less effective than chemical insecticides in practice. Despite their advantages, B.t. toxins are more likely to be repelled by genetic resistance, and thus less likely to work.

E

Birds and rodents often do greater damage to farm crops than do insects.

This states no difference between B.t. toxins and chemical insecticides that would suggest B.t. toxins are less effective or riskier than chemical insecticides. The author does not say the use of chemical insecticides harms mammals or birds.

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