7.2 Strengthening, Weakening & Evaluating Arguments

7.2 Strengthening, Weakening & Evaluating Arguments

Once you can deconstruct an argument's premises, conclusion, and assumptions, the next skill is evaluating how new evidence alters that argument's validity. These are still Reading Comprehension items — the passage is simply an argument rather than an expository extract. Strengthen, Weaken, and Evaluate questions test your ability to assess structural stability when exposed to external facts.

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Mechanics of Strengthen and Weaken Questions

In Strengthen and Weaken question types, the prompt explicitly instructs you to accept all answer options as true, even when they introduce information not mentioned in the passage. Your task is not to judge the truth of the options, but to measure how each option changes the logical gap between the stated premises and the main conclusion.

• Strengthen Questions: Require finding a choice that increases the probability that the conclusion follows from the premises.
• Weaken Questions: Require finding a choice that reduces the probability that the conclusion follows from the premises.

Crucially, weakening an argument does not mean proving the conclusion is false or proving the premises are inaccurate. A successful weakener simply demonstrates that even if the premises are 100 percent true, the conclusion does not necessarily follow.

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Common Weaken Patterns

GRE argument passages heavily feature four recurring weakener patterns:

1. Alternative Explanations (Third Variable): Demonstrating that a cause other than the one cited by the author produced the observed effect.
2. Reversed Causation: Showing that the phenomenon assumed to be the effect is actually the cause, or vice versa.
3. Unrepresentative Sample / Flawed Data: Proving that the survey group, statistical study, or trial sample used to support the premise was biased, self-selected, or corrupted.
4. Unintended Counter-Effects / Implementation Obstacles: For arguments proposing a plan, showing that executing the plan will trigger secondary consequences that defeat the main objective.

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Common Strengthen Patterns

Strengthening an argument involves fortifying the logical bridge between premise and conclusion. Four highly predictable strengthener mechanisms recur on the GRE:

1. Eliminating Alternative Causes: Explicitly ruling out competing explanations for an observed phenomenon, isolating the author's proposed cause.
2. Confirming Unstated Assumptions: Providing empirical evidence that directly verifies a necessary underlying assumption.
3. Corroborating Control Groups / Analogous Trials: Showing that when the alleged cause is absent, the effect is also absent (control group verification), or showing that identical causes produce identical effects in similar settings.
4. Validating Data and Measurement Integrity: Demonstrating that the data collection methods, instruments, or survey sample procedures were unbiased and rigorous.

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Strategy for Evaluate the Argument Questions

Evaluate the Argument questions ask you to select the inquiry or piece of information that would be most useful in determining the validity of the author's conclusion.

To solve Evaluate questions systematically, apply the Variance Test (also known as the Two-Value Test).

The Variance Test Procedure

1. For each answer choice, formulate two extreme, opposing answers (e.g., "Yes" vs. "No", or "100%" vs. "0%").
2. Insert the first extreme answer into the argument and assess the impact on the conclusion.
3. Insert the second extreme answer into the argument and assess the impact on the conclusion.
4. Decision Rule: If one extreme strongly strengthens the conclusion while the opposite extreme strongly weakens it, that answer choice is the correct evaluation inquiry. If both extremes leave the argument largely unaffected, the choice is irrelevant.

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Worked Argument Walkthrough

Passage: Oceanographers monitored marine preserve Area Alpha, where commercial fishing was banned five years ago, and noted a 40 percent increase in total fish biomass. They concluded that establishing commercial fishing bans in coastal waters is an effective method for increasing regional fish populations.

Deconstruction

• Premise: Area Alpha had a fishing ban introduced 5 years ago; fish biomass increased by 40%.
• Conclusion: Banning commercial fishing in coastal waters effectively increases regional fish populations.

Option Analysis

• Weaken Analysis: Suppose an answer choice states: "During the five-year period, ocean current shifts diverted nutrient-rich deep water into Area Alpha, triggering an unprecedented bloom of marine plankton throughout the region."

  • Evaluation: This option provides a compelling alternative explanation (nutrient-rich current shifts) for the biomass surge, undermining the claim that the fishing ban caused the population growth. It successfully weakens the argument.

• Strengthen Analysis: Suppose an answer choice states: "In nearby coastal Area Beta, where ecological conditions are identical to Area Alpha but commercial fishing continued unabated, fish biomass declined by 5 percent over the same five-year period."

  • Evaluation: This option provides a control group comparison. By showing that biomass did not increase when the fishing ban was absent, it isolates the fishing ban as the likely cause of the biomass increase in Area Alpha. It successfully strengthens the argument.

• Evaluate Analysis using the Variance Test: Consider the inquiry choice: "Whether commercial fishing fleets formerly operating in Area Alpha relocated their operations to contiguous unpreserved coastal waters."

  • Extreme 1 (YES - They relocated right outside Area Alpha): The fish population increase inside the small preserve was offset by severe depletion in surrounding waters, so overall regional fish populations did not increase. (Weakens conclusion).
  • Extreme 2 (NO - They reduced total fleet operations entirely): Total fishing pressure across the entire region declined, allowing net regional fish populations to grow. (Strengthens conclusion).
  • Result: Because the two extremes produce opposite logical impacts on the conclusion, this inquiry is crucial for evaluating the argument.