LSAT Weaken Questions Practice Questions with Answers

LSAT Weaken Questions Practice Questions with Answers

Does a specific piece of evidence always support the conclusion it claims to prove? LSAT Weaken Questions require you to identify the specific piece of information that most undermines the logical connection between an argument's premises and its conclusion. These questions appear frequently in the Logical Reasoning section, testing your ability to spot vulnerabilities, hidden assumptions, and alternative explanations in a short passage. By learning how to attack these arguments, you can significantly improve your performance on the LSAT Prep journey.

Concept Explanation

LSAT Weaken Questions focus on finding the one answer choice that, if true, would make the conclusion of an argument less likely to follow from its premises. To solve these, you must first isolate the conclusion and the supporting evidence (premises). The "weakness" usually lies in a gap where the author assumes something is true without proving it, or ignores a potential alternative cause for a phenomenon. Unlike "Must Be True" questions, you are allowed to bring in new information from the answer choices. The correct answer does not need to completely demolish the argument; it only needs to cast significant doubt on the validity of the author's reasoning.

Key Strategies for Weaken Questions

• Identify the Conclusion: Look for indicator words like "therefore," "thus," or "consequently."
• Find the Gap: Ask yourself, "Even if these premises are true, why could the conclusion still be false?"
• Focus on the Relationship: You are weakening the link between premises and conclusion, not necessarily the premises themselves.
• Look for Alternative Explanations: If the argument claims X caused Y, look for an answer that suggests Z caused Y instead.

Solved Examples

Example 1: The Health Supplement Argument

Argument: A recent study showed that people who take Vitamin C supplements daily have 20% fewer colds than those who do not. Therefore, taking Vitamin C supplements is the direct cause of the reduction in cold frequency.

1. Isolate the Conclusion: Taking Vitamin C causes fewer colds.
2. Identify the Premise: There is a correlation between Vitamin C and fewer colds.
3. Find the Flaw: The author assumes correlation equals causation.
4. Weaken: A correct answer might state: "People who take Vitamin C supplements are also more likely to exercise and wash their hands frequently." This provides an alternative cause for the fewer colds.

Example 2: The Bookstore Sales Argument

Argument: Last year, City Books increased its advertising budget by 50%. During the same period, total sales revenue increased by 10%. Thus, the advertising campaign was successful in bringing in new customers.

1. Isolate the Conclusion: The ads brought in new customers.
2. Identify the Premise: Ads went up 50% and revenue went up 10%.
3. Find the Flaw: The increase in revenue might have come from existing customers or external factors.
4. Weaken: A correct answer might state: "Last year, the only other bookstore in the city closed down." This suggests the revenue increase was due to a lack of competition, not the ads.

Example 3: The Ancient Pottery Argument

Argument: Archaeologists found fragments of a specific type of pottery in Site A and Site B, which are 500 miles apart. Because these sites are separated by a large desert, the inhabitants of Site A must have traveled by sea to trade with Site B.

1. Isolate the Conclusion: Inhabitants traveled by sea to trade.
2. Identify the Premise: Same pottery found in two distant sites separated by a desert.
3. Find the Flaw: The author assumes the only way to cross the distance was by sea.
4. Weaken: A correct answer might state: "A third site, located halfway between Site A and Site B in a fertile oasis, contains the same pottery." This suggests a land route existed via the oasis.

Practice Questions

1. The city council plans to reduce traffic congestion by increasing the toll on the main bridge during rush hour. They argue that the higher cost will encourage commuters to use the city's bus system. However, the bus system is currently operating at 95% capacity during rush hour. Which of the following most weakens the council's plan?

2. A tech company noticed that employees who work from home report higher job satisfaction than those who work in the office. The CEO concluded that to increase overall company morale, all employees should be required to work from home at least three days a week.

3. Over the last five years, the population of wolves in the National Park has doubled. During the same period, the population of deer has decreased by 30%. Therefore, the increase in the wolf population is responsible for the decline in the deer population.

4. A study found that children who play chess score significantly higher on standardized math tests than children who do not. The researchers concluded that playing chess improves a child's mathematical reasoning abilities.

5. The mayor of Oaktown claims that the new "Clean Streets" initiative is a success because the number of littering citations issued has dropped by 40% since the program began six months ago.

6. Farmers in the valley have switched to a new type of genetically modified corn that is resistant to pests. Because this corn requires fewer chemical pesticides, the farmers argue that the local groundwater will now be significantly cleaner.

7. A recent survey showed that 80% of residents in Springville prefer the new park design over the old one. Therefore, the city should proceed with the construction of the new park to satisfy the majority of its citizens.

8. The local library reports that the number of physical books checked out has decreased by 15% over the last two years. The head librarian concludes that the community's interest in reading is declining.

Answers & Explanations

1. Answer: The bus system cannot accommodate a significant influx of new riders.
   Explanation: The council's plan relies on commuters switching to the bus. If the bus is already at 95% capacity, it cannot handle the new passengers, making the plan's goal unattainable.
2. Answer: Employees who are already highly satisfied with their jobs are the ones who most frequently choose to work from home.
   Explanation: This suggests a reverse causation flaw. It’s not that working from home causes satisfaction, but that satisfied people choose to work from home.
3. Answer: A severe drought over the last five years has significantly reduced the deer's primary food source.
   Explanation: This provides an alternative explanation for the decline in the deer population, weakening the claim that wolves are the primary cause.
4. Answer: Children with high innate mathematical ability are more likely to be attracted to and persist in playing chess.
   Explanation: This points out a selection bias. The math skills might exist before the chess playing, rather than being caused by it.
5. Answer: The number of police officers assigned to patrolling for littering was reduced by 60% shortly after the program began.
   Explanation: This weakens the conclusion by showing that the drop in citations might be due to a lack of enforcement rather than a decrease in actual littering.
6. Answer: The new genetically modified corn requires a different type of fertilizer that leaches into groundwater more easily than pesticides.
   Explanation: While pesticides might decrease, the overall cleanliness of the groundwater is threatened by a new factor introduced by the same corn.
7. Answer: The survey was conducted only among residents who live within two blocks of the proposed park site.
   Explanation: This weakens the argument by showing the sample was biased and not representative of the entire population of Springville.
8. Answer: The library's digital e-book checkouts have tripled in the same two-year period.
   Explanation: This suggests that interest in reading isn't declining; rather, the medium through which people read has simply shifted from physical to digital.

Frequently Asked Questions

What is the difference between a Weaken question and a Flaw question?

A Weaken question asks you to find a new piece of information that hurts the argument, while a Flaw question asks you to describe the logical error already present in the reasoning. Essentially, Weaken questions look for external evidence, whereas Flaw questions look for internal structural problems.

Do I need to disprove the premises in a Weaken question?

No, you should generally accept the premises as true for the sake of the argument. Your task is to show that even if the premises are true, they do not necessarily lead to the conclusion the author has drawn.

Can the correct answer be something not mentioned in the stimulus?

Yes, Weaken questions specifically allow and often require "outside" information. The instructions typically state "which of the following, if true," which gives you permission to treat the answer choices as new facts.

How do I handle arguments that use percentages?

Be wary of shifts between percentages and absolute numbers. An argument might claim a 50% increase in a crime rate is devastating, but if the total number of crimes went from 2 to 3, the absolute impact is minimal, which can be a point of weakness.

What are the most common trap answers in Weaken questions?

Common traps include answers that actually strengthen the argument, answers that are irrelevant to the specific link between premise and conclusion, and answers that attack a premise rather than the logical leap to the conclusion.