Masterclass: Critical Reasoning – Strengthen • GMATCourse.mba

Core Philosophy: What "Strengthen" Really Means

A strengthen question asks you to find new information that makes the conclusion more likely to follow from the evidence. You are not verifying the evidence — you are closing the gap between premise and conclusion or providing additional support for the conclusion directly.

Strengtheners work by supporting the assumption, ruling out alternative explanations, or adding direct evidence in favour of the conclusion. The key word is "most" — find the choice that provides the greatest logical boost.

Core Insight: A strengthener makes the conclusion MORE believable given the premises — it does not have to make the conclusion certain.

Anatomy of a Strengthen Question

How Strengtheners Work

Support the Assumption

Provide evidence that the hidden bridge is true

Eliminate Alternatives

Rule out competing explanations for the evidence

Add Direct Evidence

Provide new data that directly supports the conclusion

Relevant Strengthener

Addresses the actual gap in the argument — the most efficient path.

Irrelevant Strengthener

Sounds related but doesn't actually close the gap or support the conclusion.

The Strengthen Strategy

Find the conclusion

Identify exactly what the author is claiming. Underline or mentally flag it.

Identify the underlying assumption

Ask what must be true for the evidence to support the conclusion. A strengthener often proves that assumption.

Pre-phrase what would help

Before reading choices, imagine the kind of information that would make you more confident in the conclusion.

Compare choices by degree

Two choices may both strengthen — pick the one that provides the greatest logical boost to the conclusion.

Worked Examples

Example 1 — Ruling Out Alternatives

Argument: "Students who study with background music perform worse on tests than those who study in silence. Therefore, background music impairs academic learning."

Gap: Maybe students who choose music are just less focused in general.

Best Strengthener: Studies show that identical students perform worse when randomly assigned to music-listening conditions vs. silence. (This rules out a self-selection bias.)

Example 2 — Supporting the Bridge

Argument: "Our new employee training program raised customer ratings by 18 points, so the training is responsible for the improvement."

Gap: Could external factors (seasonal trends, competitor problems) explain the rise?

Best Strengthener: Comparable companies that didn't run the training saw flat or declining customer ratings in the same period.

Example 3 — Adding Direct Evidence

Argument: "City X introduced a congestion pricing scheme and traffic fell 22%. The scheme should be adopted by other major cities."

Gap: City X may be unique — the scheme might not work elsewhere.

Best Strengthener: Every major city that has implemented congestion pricing over the past decade has seen meaningful traffic reductions, regardless of city size or geography.

10 Common Strengthen Traps

1. Out-of-scope evidence

The answer mentions a topic tangentially related but doesn't address the conclusion's premise gap.

2. Too-strong overshoot

The choice asserts something more extreme than needed — check if it actually helps or just sounds impressive.

3. Restating a premise

Repeating information already in the stimulus doesn't add any new logical weight.

4. Weakener disguised as strengthener

Some choices look relevant but actually introduce doubt about the argument.

5. Temporal mismatch

Evidence that occurred after the conclusion's stated timeframe doesn't strengthen a forward-looking claim.

6. Correlation trap

Adding another correlation to a correlation-based argument doesn't fix the underlying causation gap.

7. Wrong direction of causation

New evidence that reverses cause and effect doesn't strengthen — it may actually weaken.

8. Irrelevant comparison

Comparing two things that aren't equivalent to the argument's subject matter.

9. Double-edged choice

A choice that strengthens one part of the argument but weakens another — net effect is neutral or negative.

10. "Most" vs "some" precision

An answer that uses "some" when the conclusion requires "most" provides insufficient strength.

Strengthen vs Assumption — Quick Comparison

Feature	Strengthen	Assumption
What you need	New info that boosts the conclusion	The necessary hidden bridge
Test to apply	Does it make the conclusion more likely?	Does negating it collapse the argument?
Degree	Comparative — "most" strengthening	Binary — is this required or not?
Trap to avoid	Slight strengtheners vs. best choice	Helpful but not necessary answers

10 GMAT-Style Practice Questions

Select your answer, then reveal the step-by-step explanation. Each question reflects real GMAT difficulty and format.

Question 1 of 10 GMAT Verbal

A hospital introduced mandatory hand-washing protocols for all staff and reported a 35% reduction in hospital-acquired infections the following year. The hospital administrator concluded that the hand-washing protocol caused the reduction. Which of the following, if true, most strengthens the administrator's conclusion?

Correct Answer: (C)

(C) is correct. This strengthens by adding a second independent data point: another hospital ran the same intervention and got the same result. This makes it far more likely the protocol caused the change, not an external factor. (A) weakens — a similar reduction without the protocol suggests external causes. (B) is interesting but doesn't rule out confounders. (D) provides a mechanism but doesn't rule out alternative causes of the reduction. (E) describes the protocol detail but doesn't establish causation.

Question 2 of 10 GMAT Verbal

An energy company claims that its new wind turbines are more economically viable than coal plants because wind fuel costs nothing. A financial analyst agrees, concluding that wind energy will displace coal within 20 years. Which of the following most strengthens the analyst's conclusion?

Correct Answer: (A)

(A) is correct. The conclusion is about economic viability over time. Declining manufacturing costs directly address the primary remaining cost driver for wind energy, making the economic advantage more durable. (B) addresses policy but not economics. (C) is an environmental benefit, not economic. (D) helps wind's relative position but doesn't directly address wind's own economics. (E) is about lifespan — relevant to maintenance cost but far less impactful than (A).

Question 3 of 10 GMAT Verbal

A pharmaceutical company's internal memo states that Drug X reduces average migraine duration by 40% in clinical trials. The company concludes that Drug X will be commercially successful. Which of the following, if true, most strengthens the company's conclusion?

Correct Answer: (A)

(A) is correct. Commercial success requires a large addressable market AND competitive differentiation. (A) provides both: enormous market + Drug X is twice as effective as anything else. (B) is a strengthener but less powerful — it helps but doesn't address market size. (C) is about trial diversity — relevant to generalizability, not commercial success. (D) is about cost — helpful but less impactful than market size and differentiation. (E) confirms accuracy but doesn't add new commercial evidence.

Question 4 of 10 GMAT Verbal

A city government installed 500 new CCTV cameras in high-crime districts and reported a 28% drop in street crime the next year. Officials concluded that the cameras caused the reduction. Which of the following most strengthens the officials' conclusion?

Correct Answer: (B)

(B) is correct. The most critical threat to the causal conclusion is that crime was already falling city-wide. By showing that nearby areas WITHOUT cameras saw no change, the officials' claim that cameras caused the reduction becomes much more defensible. (A) describes where cameras were placed — doesn't help establish causation. (C) is subjective perception, not crime data. (D) is about monitoring capacity — a mechanism, not causal evidence. (E) actually introduces a confound (more police), which could weaken the causal attribution to cameras.

Question 5 of 10 GMAT Verbal

A marketing team argues that social media advertising is more effective than TV advertising for their product because their last social media campaign achieved a 12% conversion rate. Which of the following, if true, most strengthens this argument?

Correct Answer: (B)

(B) is correct. The argument is a direct comparison: social media is more effective than TV. The best strengthener is a direct comparison showing TV's conversion rate is lower. 12% vs 4% makes the argument compelling. (A) notes a demographic difference, which might actually explain the gap without proving social media is inherently better. (C) explains WHY social media might be better but doesn't prove it IS better for this product. (D) notes efficiency (faster), not higher total effectiveness. (E) addresses cost, not effectiveness.

Question 6 of 10 GMAT Verbal

A researcher concludes that eating red meat more than three times per week significantly increases the risk of cardiovascular disease, based on a 10-year study of 20,000 adults. Which of the following, if true, most strengthens the researcher's conclusion?

Correct Answer: (A)

(A) is correct. The most important threat to a dietary study is confounding variables — people who eat more red meat may also have other unhealthy habits. By stating the study controlled for key confounders, (A) significantly strengthens the causal conclusion. (B) provides a plausible mechanism but doesn't address the causation question directly. (C) actually suggests a confounder (exercise) that wasn't controlled — this weakens. (D) introduces measurement issues that could weaken the study. (E) addresses potential bias but is less impactful than controlling confounders.

Question 7 of 10 GMAT Verbal

A retail chain argues that its loyalty program is responsible for a 20% increase in repeat customer visits since its launch. Which of the following, if true, most strengthens this conclusion?

Correct Answer: (A)

(A) is correct. This provides a direct within-group comparison: program members vs. non-members. If members visit 35% more, it's strong evidence the program is driving visits rather than some external factor affecting all customers. (B) describes the program's features — doesn't prove it caused the visit increase. (C) shows a competitor's failure — interesting, but doesn't directly support this chain's conclusion. (D) is about advertising spend, not effectiveness. (E) shows satisfaction rose but doesn't directly link it to the loyalty program or visit frequency.

Question 8 of 10 GMAT Verbal

An economist claims that minimum wage increases do not cause significant unemployment because unemployment rates in regions that raised the minimum wage have not risen more than in regions that did not. Which of the following, if true, most strengthens this conclusion?

Correct Answer: (B)

(B) is correct. The key weakness in a regional comparison is confounding — perhaps regions that raised wages were economically stronger and could absorb the increase. If the study controlled for these factors, the regional comparison becomes a much stronger causal argument. (A) actually introduces a potential confounder (lower baseline), which could weaken. (C) adds a productivity benefit but doesn't address unemployment. (D) references predictions, not outcomes — irrelevant to the current evidence. (E) gives range information but doesn't address the validity of the comparison.

Question 9 of 10 GMAT Verbal

A startup claims that its AI-powered resume screening tool reduces hiring time by 50% compared to manual screening by HR staff. Which of the following most strengthens this claim?

Correct Answer: (B)

(B) is correct. A controlled, direct comparison — same role, same conditions, only the screening method changes — is the gold standard for establishing the 50% reduction. (A) is about user ratings, not actual time reduction. (C) is about cost, not time. (D) shows adoption but not time savings. (E) addresses bias, not hiring speed.

Question 10 of 10 GMAT Verbal

A nutritionist argues that the Mediterranean diet reduces the risk of type 2 diabetes better than the standard Western diet, based on observational data from several European countries. Which of the following, if true, most strengthens the nutritionist's conclusion?

Correct Answer: (A)

(A) is correct. A randomized controlled trial (RCT) is the strongest possible evidence for causation. By randomly assigning participants to diets and measuring outcomes, it eliminates selection bias and confounding. This directly strengthens the causal claim. (B) describes composition — a mechanism, not causal evidence. (C) introduces a confound (physical activity). (D) adds observational data but may have the same confounders as the original study. (E) establishes relevance but doesn't strengthen the diet-specific claim.

Key Takeaways: Strengthen Questions

1. Find the assumption first

The best strengthener usually proves the assumption or directly addresses the gap.

2. Compare by degree

Pick the choice that provides the greatest logical boost, not just any positive connection.

3. Eliminate alternative causes

Choices that rule out competing explanations are often the strongest strengtheners.

4. Watch for neutral choices

A choice that seems relevant but has zero logical impact on the conclusion is never correct.