Logical reasoning question types - Weaken questions

Learning Outcomes

After reading this article, you will be able to identify, analyze, and answer LSAT Logical Reasoning weaken questions. You will understand how to disrupt argument assumptions, recognize common logical flaws (especially cause/effect), and apply targeted strategies to select answers that most clearly undermine a given argument. You will also be able to avoid common traps and use process of elimination effectively on these questions.

LSAT Syllabus

For LSAT Logical Reasoning, you are required to understand how argument structures can be attacked and what information would most undermine an author’s conclusion. Particular focus for revision in this topic includes:

• the core principles behind weaken questions in Logical Reasoning
• identifying common flaw patterns, such as correlation vs. causation and representativeness errors
• distinguishing between directly weakening the reasoning and simply disagreeing with the conclusion
• effective techniques for eliminating attractive but incorrect weaken answers
• adapting approach for questions that ask for the most weakener

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which of the following, if true, would most weaken the reasoning in a causal argument?
   1. The effect can occur without the alleged cause.
   2. A third factor could cause both the events.
   3. There is a strong correlation but no mechanism.
   4. The cause happens after the effect.

2. True or false? A good weaken answer always directly contradicts the argument's main conclusion.

3. In a sampling argument, what kind of weaken answer is most effective?

4. What flaw is present if an argument infers that B must cause A simply because A and B occur together?

Introduction

Weaken questions are one of the most common types in LSAT Logical Reasoning. Your task is to select the answer which, if true, most clearly calls into question the argument's reasoning rather than just the conclusion itself. Successful test takers focus on the fundamental assumption or flaw and target that point of weakness, rather than choosing answers that simply introduce general doubt.

Key Term: weaken question
A Logical Reasoning question type that asks you to pick an answer that, if true, makes the argument less persuasive by attacking its reasoning.

Argument Structure in Weaken Questions

Most weaken questions present a short argument with a clear conclusion supported by one or more premises. Unlike flaw questions (which ask you to explain the problem), weaken questions require you to pick new information that exploits a flaw, assumption, or gap.

Typical Question Stems

• "Which one of the following, if true, most seriously weakens the argument?"
• "Which of the following, if true, most undermines the reasoning above?"
• "Which one of the following, if true, most calls into question the author's conclusion?"

The phrase "if true" acts as a signal: you must assume each answer choice is correct, even if it’s unlikely in real life.

Weaken vs. Contradict

The correct weaken answer need not directly contradict the conclusion. Instead, it most effectively challenges the reasoning or exposes a vulnerability.

Worked Example 1.1

An argument states: "Last year, new bike lanes were installed, and overall traffic accidents declined. Therefore, installing bike lanes causes traffic accidents to decrease."

Which choice most weakens this argument?

A) The city also lowered speed limits last year.
B) Fewer people drove during the year because of remote work.
C) New bike lanes replaced roads where most past accidents occurred.
D) Accidents involving cyclists actually increased.

Answer:
A and B both weaken the claim by suggesting alternative causes for the decline. They introduce confounding variables, showing that reduced accidents could have other explanations—not just the new bike lanes.

Spotting Common Weaken Patterns

Most strong weaken answers exploit these patterns:

• Introducing an alternative cause in causal arguments
• Showing the effect occurs without the stated cause or can occur with other factors
• Highlighting nonrepresentative data in sampling arguments
• Demonstrating the analogy or comparison breaks down

Key Term: assumption
An unstated idea that must be true for the argument to work; attacking the key assumption is often the best weaken strategy.

Key Term: causal reasoning
A line of reasoning that says one thing causes another; often vulnerable if other plausible causes are possible.

Key Term: sampling argument
An argument that draws a conclusion about a population from a subset; correct weakeners often show the sample is unrepresentative.

Worked Example 1.2

Stimulus: "A survey of local dog owners found that most prefer walking dogs in the evening. Therefore, all dog owners likely prefer evenings for dog walks."

Which choice most weakens the conclusion?
A) The survey polled only owners at one park open only after 5pm.
B) Some dog owners walk dogs at midday for work convenience.
C) Dog walking preferences can differ on weekends.
D) Some owners do not answer surveys.

Answer:
A is the correct weakener: It exposes an unrepresentative sample, undermining the conclusion about all dog owners.

Strategies for Weaken Questions

1. Quickly identify the premise(s), conclusion, and especially the assumption linking them.
2. Ask: What must be true for the argument to succeed? If that point is false or undermined, the argument collapses.
3. Evaluate each answer as "if true"—does it attack the gap or flaw, or does it merely add noise?
4. Be alert to answers that simply contradict the conclusion. Unless they specifically target the reasoning, these are rarely credited.
5. Eliminate answers which rephrase or slightly weaken a premise (the best answers attack the logical connection).

Revision Tip

On weaken questions, always ask yourself: What would the author be most surprised to discover is true? That is often your answer.

Worked Example 1.3

Argument: "Students who eat breakfast score higher on exams, so eating breakfast causes better exam performance."

Which of the following most weakens the argument?
A) Students who eat breakfast usually have parents reminding them.
B) Exam days are often stressful for all students.
C) Schools with breakfast programs have more practice tests.
D) Some high performers skip breakfast.

Answer:
A is the best weakener—it introduces a possible confounder (parental involvement) showing that something other than breakfast might boost test performance.

Types of Flaws Exploited by Weaken Answers

Causation vs. Correlation

Many LSAT arguments confuse correlation (events happening together) with causation (one event causing the other).

Key Term: correlation vs. causation flaw
Mistaking correlation as evidence of a direct causal link; correct weaken answers often propose another plausible cause, or show the effect happens without the supposed cause.

Overlooking Alternatives

Arguments that fail to rule out other possible causes or factors are especially vulnerable.

Nonrepresentative Data

Weaken answers may show the data/sample does not justify the generalization. This is common in survey or poll-based arguments.

False Analogy

Arguments drawing conclusions from an inapt or incomplete analogy are weakened by showing relevant dissimilarities.

Exam Warning

In weaken questions, answers that simply make the conclusion less likely but do not target the argument’s specific gap rarely earn credit.

Summary Table: Common Flaw Targets in Weaken Questions

Key Point Checklist

This article has covered the following key knowledge points:

• The correct weaken answer targets the argument's logical gap or assumption, not just the conclusion
• Most weaken answers exploit flaws involving causation, sampling, or faulty analogies
• Causal/ correlation arguments are often undermined by presenting other potential causes
• Representative sampling is required: weak samples, cherry-picked data, or biased sources can undermine arguments
• Always treat answer choices as hypothetically true
• Use process of elimination—eliminate answers that miss the logical target, even if they sound reasonable

Key Terms and Concepts

• weaken question
• assumption
• causal reasoning
• sampling argument
• correlation vs. causation flaw