7.3 Strengthen Questions: Supporting Premises, Causality, and New Evidence

7.3 Strengthen Questions: Supporting Premises, Causality, and New Evidence

Quick Summary: Strengthen questions ask you to identify a new piece of information that, if assumed to be true, makes the author's conclusion more plausible. Unlike necessary assumption questions—which demand minimal, unstated prerequisites—strengthen questions welcome powerful, decisive new evidence. The vast majority of GMAT strengthen arguments involve Causality ($X \implies Y$). To strengthen a causal claim, your primary strategies are: (1) eliminate an alternate cause, (2) show that when the cause is absent, the effect is absent, (3) rule out reverse causality, or (4) validate the underlying data methodology.

Strengthen questions are among the most common question formats in the Verbal Reasoning section of the GMAT Focus Edition. They evaluate your ability to assess evidentiary weight and determine how new facts influence an existing argument.

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The Mechanics of Strengthening: The "If True" Standard

Understanding the question stem is vital. Typical stems include:

• "Which of the following, if true, most strongly supports the argument above?"
• "Which of the following, if true, provides the strongest additional justification for the plan?"
• "Which of the following, if true, would most bolster the researchers' hypothesis?"

Two Critical Ground Rules

1. Answer Choices Are Accepted as 100% True: The phrase "if true" grants each answer choice absolute factual status. You cannot dismiss a choice by thinking, "That sounds unlikely in the real world." Accept the statement as a rock-solid fact, then measure its logical impact on the stimulus.
2. Outside Information Is Expected: In Reading Comprehension and Inference questions, bringing in outside information is fatal. In Strengthen questions, however, the correct answer must bring in new information. Your job is to determine which new fact fits like a key into the argument's unstated vulnerability.

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Causation vs. Correlation: The Engine of Critical Reasoning

Most GMAT arguments rely on a causal conclusion: the author observes a statistical correlation or temporal sequence between two events ($X$ and $Y$) and asserts that $X$ caused $Y$.

$\text{Correlation: } X \text{ and } Y \text{ occur together} \quad \not\implies \quad \text{Causation: } X \text{ caused } Y$

Whenever a GMAT author claims that $X$ caused $Y$, formal logic dictates that exactly four possibilities exist:

1. $X$ caused $Y$ (The author's hypothesis)
2. $Y$ caused $X$ (Reverse causality)
3. $Z$ caused both $X$ and $Y$ (An unmeasured third factor / confounding variable)
4. Coincidence (The correlation is pure statistical noise)

To strengthen the claim that $X$ caused $Y$, an answer choice must make possibility 1 more likely by attacking or eliminating possibilities 2, 3, or 4.

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The Five Universal Causal Strengthener Archetypes

When evaluating choices on a causal strengthen question, look for one of these five proven structural patterns:

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Strengthening Plan and Policy Arguments

Many Critical Reasoning arguments do not argue scientific causality; instead, they propose a Plan or Policy to achieve a specific goal:

$\text{Current Problem} \longrightarrow \mathbf{\text{Proposed Plan (Action)}} \longrightarrow \mathbf{\text{Intended Goal}}$

To strengthen a plan-based argument, the correct answer must demonstrate one of three operational conditions:

• Feasibility: The plan is practical, affordable, and capable of being executed within existing constraints.
• Efficacy: The proposed action directly removes the root obstacle causing the problem.
• Absence of Countervailing Forces: The plan will not trigger unintended secondary side effects that cancel out the benefits.

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Complete Worked GMAT Stimulus Breakdown

Stimulus: Marine biologists studying coral reefs in the Coral Triangle observed that reefs located adjacent to active seaweed farms exhibited 45% less coral bleaching during an extreme marine heatwave than did nearby reefs located far from seaweed farms. Seaweed absorbs large quantities of dissolved carbon dioxide through photosynthesis, which locally dampens seawater acidification. The researchers concluded that the presence of commercial seaweed farms protects adjacent coral reefs from thermal bleaching during heatwaves.

Structural Deconstruction

• Observed Correlation: Reefs near seaweed farms had 45% less bleaching during a heatwave than reefs far from seaweed farms.
• Proposed Cause: Seaweed photosynthesis dampens acidification, protecting corals.
• Main Conclusion (Causal): Commercial seaweed farms protect adjacent coral reefs from thermal bleaching during heatwaves ($X \implies Y$).
• Vulnerability: Did the seaweed farms cause the protection, or were the seaweed farms deliberately placed in areas that already had cooler upwelling currents or naturally resilient coral species (an alternate cause $Z$)?

Choice-by-Choice Analysis

Question Stem: Which of the following, if true, most strongly supports the researchers' conclusion?

• Choice A (Distractor: Irrelevant Comparison): Corals in other ocean basins, such as the Caribbean, experience bleaching at temperatures slightly lower than corals in the Coral Triangle.
  Analysis: This describes baseline temperature tolerances across different global regions. It provides zero insight into whether seaweed farms protected the specific reefs in the Coral Triangle.
• Choice B (Correct: Rule Out Alternate Cause / Reverse Causality): Seaweed farmers in the Coral Triangle do not selectively site their farms in locations with cooler water temperatures or stronger protective tidal currents.
  Analysis: If farmers deliberately picked sites with naturally cooler water or protective currents, those geographic features—not the seaweed—would explain the reduced bleaching. By ruling out this major confounding variable, Choice B establishes that the coral survived because of the farms, strongly supporting the researchers' causal conclusion.
• Choice C (Distractor: Premise Booster): Laboratory measurements confirm that the species of seaweed cultivated on these farms absorbs carbon dioxide at a rate higher than most wild seaweed species.
  Analysis: The stimulus already stated as a fact that the seaweed absorbs large quantities of carbon dioxide. Proving this fact again does not bridge the inferential gap between carbon absorption and thermal bleaching survival.
• Choice D (Distractor: Weakener): Harvesting mature seaweed from the farms temporarily stirs up fine sediments that cloud the surrounding water for several days.
  Analysis: Turbid water might reduce light exposure, but sedimentation can also smother corals. If anything, this introduces an environmental hazard, mildly weakening rather than strengthening the benefits of the farms.
• Choice E (Distractor: Out of Scope / Economic Viability): Commercial demand for farmed seaweed products has grown steadily over the past decade in Southeast Asia.
  Analysis: Market demand addresses the financial viability of seaweed farming, which has no logical relevance to the biological question of whether seaweed protects coral from heat stress.

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High-Frequency GMAT Traps in Strengthen Questions

• Trap 1: The "Premise Booster": The most insidious GMAT trap. It provides spectacular new evidence proving that a stated premise is true. Remember: premises do not need help! The GMAT rules require you to take stated premises as 100% true. You must strengthen the inference connecting premise to conclusion, not the premise itself.
• Trap 2: The "Opposite" (Weaker): In the rush of exam conditions, candidates often misread the stem or misunderstand the argument's direction, choosing a statement that casts doubt on the author's claim.
• Trap 3: Supporting an Unstated, Favorable Outcome: If an argument claims that a tax cut will reduce government deficits, an answer choice stating that "citizens were very happy with the tax cut" is irrelevant. Happiness does not prove deficit reduction.
• Trap 4: Extreme Language Paranoia: Unlike in Necessary Assumption questions—where extreme language is dangerous—in Strengthen questions, strong language is often desirable. A choice stating "In every single observed test, removing the factor eliminated the outcome" is far more powerful than a choice stating "Occasionally, removing the factor helped."