LSAT Logical Reasoning
Weaken Questions

Master the art of identifying information that undermines an argument's conclusion by attacking its assumptions.

LSAT Logical Reasoning

What Is a Weaken Question?

A weaken question asks you to find the answer choice that makes the argument's conclusion less likely to be true. You are not trying to destroy the argument entirely: you just need to reduce the support for the conclusion.

Anatomy of an Argument

Recognizing Weaken Question Stems

The LSAT signals a weaken question with specific language. Learn to spot these keywords instantly so you know what task you are performing.

Classic Stems

"Which most seriously weakens the argument?"
"Which most undermines the reasoning?"

Variant Stems

"Which calls into question the conclusion?"
"Which casts doubt on the argument above?"

Tricky Stems

"Which provides the strongest objection?"
"Which provides a reason to doubt?"

The Core Rule of Weakening

Types of Assumptions to Attack

Causal

Assumes X causes Y. Weaken by showing an alternative cause, or that the correlation is coincidental.

Analogical

Assumes two things are similar. Weaken by showing a relevant difference between them.

Statistical

Assumes a sample represents the whole. Weaken by showing the sample is biased or unrepresentative.

Weaken vs. Strengthen vs. Flaw

	Weaken	Strengthen	Flaw
Task	Undermine the conclusion	Support the conclusion	Describe the reasoning error
Answer Type	New information	New information	Description of logic
Focus	Assumption gap	Assumption gap	Structural error
Adds Facts?	Yes	Yes	No

How to Solve Weaken Questions

1

Read the question stem first. Confirm it is a weaken question by identifying keywords like "undermines" or "weakens."

2

Identify the conclusion. Find exactly what the author is claiming. Look for indicator words: "therefore," "thus," "hence," "must be."

3

Identify the premises. What evidence is offered? What facts are stated?

4

Find the assumption (the gap). What must be true for the premises to support the conclusion?

5

Choose the answer that attacks the assumption. The correct answer introduces a fact that makes the conclusion less likely.

Worked Example: Causal Argument

Worked Example: Analogy-Based Argument

1

Conclusion: City B should add a toll road.

2

Premise: City A's toll road reduced congestion.

3

Assumption: City A and City B are similar enough that the same solution will work.

4

Weakener: "City B's congestion is caused by inadequate public transit, not the road structure that toll roads address." This shows a relevant difference.

Worked Example: Statistical Argument

Eliminating Wrong Answer Choices

Irrelevant

Introduces a fact that has no connection to the argument's premises, conclusion, or assumption.

Strengthener

Makes the conclusion more likely. This is the opposite of what you need.

Out of Scope

Discusses something beyond what the argument addresses. Tempting but does not weaken.

A Quick Confirmation Trick

If you think an answer choice weakens the argument, you can confirm it by considering its logical opposite. Because Weaken and Strengthen choices are opposites, the negation of a weakener should strengthen the argument.

1

Take your potential weakener and state its logical opposite. For example, the opposite of "The sample was biased" is "The sample was not biased."

2

Ask: Does this opposite statement make the original conclusion more likely to be true?

3

If yes: your original choice is a valid weakener. If no: it likely has no effect, and you should reconsider it.

Degree Matters: "Most" Seriously Weakens

The LSAT often asks which answer "most" weakens or "most seriously undermines." This means multiple choices may weaken the argument to some degree. Your job is to pick the one with the greatest impact.

Common Mistakes

Picking a Strengthener

Under pressure, students accidentally choose an answer that supports the conclusion instead of undermining it.

Attacking Premises

The correct answer never says the premises are false. Premises are taken as given. Attack the link to the conclusion.

Going Out of Scope

Choosing an answer about a topic the argument never discussed. It may sound relevant but has no impact on the specific conclusion.

Summary: Weakening by Argument Type

Argument Type	Assumption	How to Weaken
Causal	X causes Y	Alternative cause or reverse causation
Analogical	A and B are similar	Relevant difference between A and B
Statistical	Sample represents whole	Biased or unrepresentative sample
Conditional	If P then Q applies	Exception where P holds but Q fails
Prescriptive	Plan will achieve goal	Implementation problem or side effect

Question 1 of 5

Researcher: Studies show that students who eat breakfast score higher on standardized tests than those who skip breakfast. Therefore, schools should provide free breakfast to all students in order to raise test scores.

Tap to read passage

Which of the following, if true, most weakens the researcher's argument?

The argument assumes that breakfast itself causes higher scores. Choice C shows that students who eat breakfast come from more educationally supportive homes: the higher scores may be due to home environment, not breakfast. This provides an alternative cause, directly undermining the causal assumption.

Question 2 of 5

City Planner: Greenville's new bike-lane program led to a 30% increase in cycling. Riverside has similar demographics and traffic patterns. Riverside should therefore adopt the same bike-lane program to increase cycling.

Tap to read passage

Which of the following, if true, most seriously undermines the city planner's reasoning?

This is an analogical argument: it assumes Greenville and Riverside are similar enough for the same solution to work. Choice B reveals a relevant difference (hilly terrain) that would prevent the bike-lane program from achieving the same result, directly attacking the analogy.

Question 3 of 5

Journalist: A poll of 500 attendees at an environmental conference found that 92% support a nationwide ban on single-use plastics. Clearly, the general public overwhelmingly supports such a ban.

Tap to read passage

Which of the following, if true, most weakens the journalist's conclusion?

This is a statistical argument that generalizes from a sample to a population. Choice A shows the sample is biased: environmental conference attendees are not representative of the general public. This directly attacks the assumption that the sample reflects broader opinion.

Question 4 of 5

Manager: Our company switched to an open-office layout six months ago. Since the switch, employee satisfaction scores have declined by 15%. The open-office layout must be the cause of lower employee satisfaction.

Tap to read passage

Which of the following, if true, most calls into question the manager's conclusion?

The manager makes a causal argument: the open office caused the decline. Choice D introduces an alternative cause (salary freeze and benefit cuts) that could independently explain the drop in satisfaction, undermining the assumption that the office layout was responsible.

Question 5 of 5

Mayor: Our city's new after-school tutoring program will reduce the dropout rate. The program provides free tutoring three days a week to any high school student who requests it. Since academic difficulty is the primary reason students drop out, providing academic support will keep them in school.

Tap to read passage

Which of the following, if true, most weakens the mayor's argument?

This is a prescriptive argument: a plan is proposed to achieve a goal. Choice B reveals an implementation problem: the students who most need the program cannot attend it because they work after school. The plan fails to reach its target audience, so it is unlikely to reduce the dropout rate as claimed.

LSAT Logical ReasoningWeaken Questions

What Is a Weaken Question?

Anatomy of an Argument

Recognizing Weaken Question Stems

The Core Rule of Weakening

Types of Assumptions to Attack

Weaken vs. Strengthen vs. Flaw

How to Solve Weaken Questions

Worked Example: Causal Argument

Worked Example: Analogy-Based Argument

Worked Example: Statistical Argument

Eliminating Wrong Answer Choices

A Quick Confirmation Trick

Degree Matters: "Most" Seriously Weakens

Common Mistakes

Summary: Weakening by Argument Type

Question 1 of 5

Question 2 of 5

Question 3 of 5

Question 4 of 5

Question 5 of 5

LSAT Logical Reasoning
Weaken Questions