Medium LSAT Flaw Questions With Answers Practice Questions

Medium LSAT Flaw Questions With Answers Practice Questions

Logical reasoning on the LSAT requires you to spot the specific gap between an author's evidence and their conclusion. Medium LSAT Flaw Questions With Answers Practice Questions focus on identifying these errors in logic, which typically involve common fallacies such as correlation versus causation, circular reasoning, or sampling errors. Developing this skill is essential for the LSAT Prep journey, as flaw questions account for a significant portion of the Logical Reasoning section.

Concept Explanation

An LSAT flaw is a specific reasoning error where the conclusion of an argument is not fully supported by its premises. These questions ask you to identify the "vulnerability" or "error in reasoning" that makes the argument invalid. Unlike "Strengthen" or "Weaken" questions, you are not looking for new information; instead, you are describing why the internal logic already present in the stimulus is broken. Common medium-level flaws include confusing a necessary condition for a sufficient one, making an illicit appeal to authority, or failing to consider alternative explanations for a phenomenon. According to formal logic principles, an argument is flawed if the truth of the premises does not guarantee the truth of the conclusion.

Solved Examples

1. The Correlation Flaw: An ice cream shop owner noticed that whenever ice cream sales increase, the number of sunburns reported at the local clinic also increases. Therefore, the owner concluded that eating ice cream causes sunburns.
   1. Identify the Premise: Ice cream sales and sunburns increase together.
   2. Identify the Conclusion: Eating ice cream causes sunburns.
   3. Identify the Flaw: The argument assumes that because two things happen at the same time, one must cause the other, ignoring a common cause (like hot weather).
2. The Necessary/Sufficient Flaw: To graduate from this university, a student must pass a swimming test. Sarah passed the swimming test yesterday, so she will definitely graduate this semester.
   1. Identify the Premise: Passing the test is a requirement (necessary). Sarah passed the test.
   2. Identify the Conclusion: Sarah will graduate.
   3. Identify the Flaw: The argument treats a necessary condition (passing the test) as a sufficient condition (guaranteeing graduation).
3. The Ad Hominem Flaw: Dr. Smith argues that the new city park will improve local air quality. However, Dr. Smith was once arrested for a noise violation, so we should ignore his environmental recommendations.
   1. Identify the Premise: Dr. Smith has a past legal issue.
   2. Identify the Conclusion: His argument about air quality is invalid.
   3. Identify the Flaw: The argument attacks the person's character rather than addressing the merits of the scientific claim.

Practice Questions

1. Every time the local professional basketball team plays in their blue jerseys, they win. They are wearing their blue jerseys tonight, so they are certain to win the game. Which of the following describes the flaw in the reasoning above?

2. A survey of 50 professional athletes found that 90% of them prefer brand X sneakers over brand Y. Therefore, brand X is clearly the superior sneaker for the general public. The argument's reasoning is most vulnerable to criticism on the grounds that it...

3. The mayor claims that the new tax will fund public schools. But the mayor is known for being dishonest in her personal life. Thus, the new tax will likely not fund public schools. The reasoning in the argument is flawed because it...

4. If a person is a lawyer, they must have passed a bar exam. John has passed a bar exam, so John must be a lawyer. Which of the following best describes the error in logic?

5. The company's profits increased by 20% after they hired a new consultant. Clearly, the consultant's advice was the reason for the profit increase. The argument is flawed because it fails to consider...

6. No one has ever proven that ghosts do not exist. Therefore, it is reasonable to conclude that ghosts are real. This argument is vulnerable to criticism because it...

7. The new smartphone is the best on the market because it has the highest-rated camera. A high-rated camera is the most important feature of a smartphone. Therefore, this smartphone is the best. The reasoning is flawed because it...

8. Most people who own luxury cars also own their own homes. Therefore, if you buy a luxury car, you will be much more likely to become a homeowner. The argument contains which of the following flaws?

Answers & Explanations

1. Answer: Confuses correlation with causation. The argument assumes that wearing the jerseys causes the win, rather than it being a coincidence or a result of other factors. This is a classic "post hoc ergo propter hoc" error often seen in critical reading assessments.

2. Answer: Relies on a biased or unrepresentative sample. Professional athletes have different physical needs than the general public. What works for them may not be superior for an average person, making the sample unrepresentative of the conclusion's target group.

3. Answer: Attacks the source of the claim rather than the claim itself. This is an ad hominem attack. The mayor's personal honesty does not logically dictate the actual destination of tax funds, which is determined by law and policy.

4. Answer: Mistakes a necessary condition for a sufficient one. Passing the bar is necessary to be a lawyer, but it is not sufficient; one could pass the bar but choose a different profession, like being a law professor or a consultant.

5. Answer: The possibility of external factors. The argument ignores other variables, such as a general economic upturn or a competitor going out of business, which could have caused the profit increase regardless of the consultant.

6. Answer: Appeals to ignorance. The lack of evidence against a claim is not positive evidence for that claim. Failing to disprove something does not make it true.

7. Answer: Circular reasoning. The argument assumes what it sets out to prove. It defines the "best" smartphone by the camera, and then uses the camera rating to prove it is the best. You can practice similar logic structures using the AI Question Generator for customized drills.

8. Answer: Reverses the likely direction of cause and effect. It is more likely that having the wealth to afford a home also allows one to afford a luxury car, rather than the car causing the homeownership.

Frequently Asked Questions

What is the difference between a flaw and a weakener?

A flaw question asks you to describe an existing error in the argument's logic, whereas a weakener asks you to provide new information that makes the conclusion less likely. Flaw questions are descriptive of the current text, while weakeners are proactive.

How can I identify a circular reasoning flaw?

Circular reasoning occurs when the conclusion is simply a restatement of the premise in different words. If you find yourself saying "this is true because it's true," you have identified a circular argument where no actual evidence is provided.

What is the "Necessary vs. Sufficient" flaw?

This error occurs when an author treats a requirement (something that must happen) as a guarantee (something that ensures the outcome). For example, having a key is necessary to start a car, but having a key does not guarantee the car will start if the battery is dead.

Why are sampling flaws common on the LSAT?

Sampling flaws test your ability to recognize when a group used in a study does not accurately represent the group mentioned in the conclusion. These are frequent because they mirror real-world errors in data interpretation and analytical reasoning.

Can an argument have more than one flaw?

Yes, an argument can contain multiple logical errors, but the LSAT will typically focus on one primary flaw in the answer choices. Your goal is to find the description that accurately matches the most significant gap in the stimulus's logic.