Medium LSAT Flaw Practice Test Practice Questions

Medium LSAT Flaw Practice Test Practice Questions

Identifying logical errors is a fundamental requirement for success on the Law School Admission Test, as approximately 15% of Logical Reasoning questions focus specifically on identifying flaws. This Medium LSAT Flaw Practice Test Practice Questions guide focuses on the intermediate level of difficulty, where arguments are more complex and the errors are more subtly disguised than in introductory drills.

Concept Explanation

An LSAT flaw is a specific logical error in an argument where the premises provided do not adequately support the conclusion reached. In the context of LSAT Prep, these flaws typically fall into recognizable categories such as Correlation vs. Causation, Ad Hominem attacks, Circular Reasoning, and Part-to-Whole fallacies. To identify a flaw, one must first isolate the conclusion and the evidence, then ask: "Why does this evidence fail to prove this conclusion?" The answer usually involves a gap in logic where the author assumes something is true without providing proof. Understanding these patterns is essential for anyone using an AI Exam Simulator to mimic real test conditions.

Solved Examples

1. Example 1: Correlation vs. Causation
   Argument: Every time the local high school holds a pep rally, the football team wins its game the following day. Therefore, the pep rallies are clearly causing the team to win.
   Step-by-Step Solution:
   1. Identify the Conclusion: Pep rallies cause the team to win.
   2. Identify the Evidence: There is a temporal sequence where rallies happen before wins.
   3. Identify the Flaw: The author assumes that because event A happens before event B, A must cause B. This ignores other factors, such as the team's skill or the quality of the opponent.
2. Example 2: Source Attack (Ad Hominem)
   Argument: Dr. Smith argues that the new city park will improve public health. However, Dr. Smith stands to profit from the construction contract. Thus, his argument about public health must be false.
   Step-by-Step Solution:
   1. Identify the Conclusion: Dr. Smith's argument is false.
   2. Identify the Evidence: Dr. Smith has a personal financial interest in the outcome.
   3. Identify the Flaw: The author attacks the person making the argument rather than the merits of the argument itself. A biased person can still tell the truth.
3. Example 3: Necessary vs. Sufficient
   Argument: To get an A in this class, you must submit all your homework. Sarah submitted all her homework, so she will definitely get an A.
   Step-by-Step Solution:
   1. Identify the Conclusion: Sarah will get an A.
   2. Identify the Evidence: Submitting homework is required (necessary) for an A, and Sarah met that requirement.
   3. Identify the Flaw: The author treats a necessary condition as if it were a sufficient one. Just because you must do something to succeed doesn't mean doing it guarantees success.

Practice Questions

1. A recent study showed that people who eat breakfast every morning are 20% less likely to be overweight than those who skip it. Therefore, if you want to lose weight, you should start eating breakfast. The argument is flawed because it:

1. Fails to consider that some people who eat breakfast may still be overweight.
2. Confuses a correlation between two factors with a causal relationship.
3. Relies on a sample size that is likely too small to be representative.
4. Assumes that what is true for a group must be true for every individual.

2. The mayor’s proposal to increase property taxes is clearly misguided. After all, the mayor has failed to manage his own personal finances effectively for years. The reasoning in the argument is most vulnerable to criticism on the grounds that it:

1. Presumes that a policy cannot be effective if the person proposing it is unpopular.
2. Attacks the character of the proposer rather than the substance of the proposal.
3. Fails to provide evidence that property taxes are already too high.
4. Mistakes a necessary condition for a sufficient one.

3. If the library receives the new grant, it will be able to stay open until midnight. The library did not receive the grant, so it will not be able to stay open until midnight. Which of the following describes the flaw in the argument?

1. It ignores the possibility that the library could stay open late using other funding sources.
2. It assumes that staying open late is the only benefit of receiving a grant.
3. It treats a condition that is sufficient for an outcome as if it were necessary.
4. It circularity assumes the conclusion in its premises.

4. Most successful CEOs play golf. Therefore, if you want to become a successful CEO, you should take up golf. The flaw in this reasoning is most similar to which of the following?

1. Most birds can fly, so this creature must be a bird because it is flying.
2. Most people who own umbrellas are prepared for rain, so owning an umbrella causes rain.
3. Most championship runners wear brand-name shoes, so wearing brand-name shoes will make you a champion.
4. Most doctors recommend exercise, so exercise must be the only way to stay healthy.

5. Every ingredient in this soup is delicious. Therefore, the soup itself must be delicious. This argument is flawed because it:

1. Uses a term in two different senses throughout the argument.
2. Assumes that a property of the parts must also be a property of the whole.
3. Relies on the testimony of experts who are not qualified in the field.
4. Fails to define what constitutes a "delicious" ingredient.

6. No one has ever proven that ghosts do not exist. Therefore, it is reasonable to conclude that ghosts do exist. The argument's reasoning is flawed because it:

1. Treats a lack of evidence for a claim as evidence for the opposite claim.
2. Relies on emotional appeals rather than logical evidence.
3. Assumes that because a belief is popular, it must be true.
4. Uses circular reasoning to support its conclusion.
5. Fails to provide a specific definition of "ghosts."

7. The new software update was intended to reduce system crashes. Since the update was installed, system crashes have decreased by 50%. Thus, the update was successful in achieving its goal. Which of the following, if true, most highlights a flaw in the argument?

1. The system crashes were already decreasing before the update was installed.
2. Some users found the new software interface difficult to navigate.
3. The update cost more to develop than the company originally anticipated.
4. A different software update was released by a competitor at the same time.

8. Either we must increase the military budget or we will be vulnerable to invasion. We cannot afford to be vulnerable to invasion, so we must increase the military budget. The flaw in the argument is that it:

1. Assumes that the military budget is the only factor in national security.
2. Fails to consider other ways of preventing an invasion besides increasing the budget.
3. Uses inflammatory language to distract the reader from the facts.
4. Presents a false dilemma by limiting the options to only two.

Answers & Explanations

1. Answer: B. The argument observes a correlation (breakfast and lower weight) and concludes a causal link (eating breakfast causes weight loss). It ignores that a third factor, like overall health consciousness, could cause both.
2. Answer: B. This is a classic ad hominem flaw. The mayor's personal financial history is irrelevant to whether the property tax policy itself is logically sound or beneficial for the city.
3. Answer: C. The first sentence establishes that the grant is sufficient to stay open late. The conclusion treats it as necessary (denying the antecedent). For more on logical structures, check our verbal reasoning guides.
4. Answer: C. This is a "mistaking correlation for causation" flaw. Just because successful people share a trait (golf/shoes) doesn't mean the trait causes the success.
5. Answer: B. This is the Fallacy of Composition. Just because individual parts (ingredients) have a quality (delicious) doesn't mean the combination (soup) will share that quality—especially if the ingredients don't pair well.
6. Answer: A. This is an Appeal to Ignorance. Absence of evidence is not evidence of absence (or presence).
7. Answer: A. This points to a "False Cause" flaw. If the trend was already occurring, the update might not be the cause of the decrease, which is a common focus in reading comprehension analysis.
8. Answer: D. The argument presents only two extreme options (increase budget or be invaded), ignoring middle-ground solutions like diplomatic treaties or restructuring existing funds.

Frequently Asked Questions

What is the most common flaw on the LSAT?

The most frequent flaw is confusing correlation with causation, where an author assumes that because two things happen together, one must cause the other. This often appears in both Logical Reasoning and Reading Comprehension sections.

How do I distinguish between a Straw Man and an Ad Hominem?

An Ad Hominem attacks the person's character or motives, while a Straw Man misrepresents the person's actual argument to make it easier to attack. One targets the individual, while the other targets a distorted version of the logic.

Can a necessary condition also be a sufficient condition?

Yes, in some cases a condition can be both, but the LSAT flaw usually involves the author incorrectly assuming a condition is sufficient just because it is necessary. In formal logic, this is known as the fallacy of affirming the consequent.

Why are flaw questions considered "medium" difficulty?

Medium difficulty flaw questions often use abstract language or nested conditional statements to hide the logical gap. They require a higher level of precision than basic questions, which you can practice using our AI Flashcard Generator.

Is circular reasoning common on the actual LSAT?

Circular reasoning is relatively rare as the correct answer, but it is a very common "distractor" or wrong answer choice. You should only select it if the premise and conclusion are logically identical.