15.2 Strengthening, Weakening & Evaluating Logical Arguments

Strengthening, Weakening & Evaluating Logical Arguments

Once an argument has been deconstructed into its constituent premises, assumptions, and conclusion, NTS Analytical Reasoning questions test your ability to evaluate its logical strength. Questions will prompt you to select an answer choice that either strengthens (supports), weakens (undermines), or pinpoints a structural fallacy in the passage's reasoning. Mastering these items requires a clear operational understanding of how new information alters the probability of a conclusion.

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Mechanics of Strengthening Logical Arguments

To strengthen an argument, you must select an answer choice that increases the probability that the author's conclusion is true. It is critical to recognize that a strengthening statement does not need to prove the conclusion with 100% absolute certainty; it merely needs to bolster the link between the premises and the conclusion.

3 Primary Strengthening Strategies

1. Ruling Out Alternative Causes: In causal arguments (Claim: Cause A produced Effect B), demonstrating that no external confounding variable Z could have caused B strongly reinforces A as the genuine cause.
2. Validating the Key Assumption: Explicitly providing empirical proof that confirms an unstated, necessary assumption is true in the real world.
3. Providing Corroborating Empirical Data or Parallel Cases: Introducing independent external data showing that whenever Cause A is present in similar environments, Effect B consistently occurs.

       [Stated Premise: Factor A occurred, followed by Outcome B]
                                  |
         +------------------------+------------------------+
         |                                                 |
[Strengthening Mechanisms]                        [Weakening Mechanisms]
  - Rules out alternate cause Z                     - Proves alternate cause Z produced B
  - Confirms key unstated assumption                - Shows B occurred before A
  - Shows A -> B holds in control tests             - Exposes biased sample / bad data

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Mechanics of Weakening Logical Arguments

To weaken an argument, you must select an answer choice that casts maximum doubt on the validity of the conclusion while fully accepting the stated premises as factual truth.

Cardinal NTS Rule: Never select an option that directly contradicts or denies a stated premise. On the GAT exam, premises are accepted as given truths. A valid weakening option accepts the premises as true but demonstrates why the conclusion does not necessarily follow.

3 Primary Weakening Strategies

1. Introducing a Competing Alternative Cause: Demonstrating that an unmentioned external factor Z was actually responsible for Effect B, rendering Cause A irrelevant.
2. Demonstrating Reverse Causality or Counter-Examples: Showing instances where Cause A occurred but Effect B failed to occur, or proving that Effect B actually preceded Cause A in chronological time.
3. Exposing Methodological or Sampling Flaws: Demonstrating that the data, survey, or sample relied upon in the premise is unrepresentative, biased, or measured using flawed metrics.

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Dissecting Causal Reasoning & Common Fallacies

A large majority of NTS argument evaluation questions center on causal claims. Authors frequently observe a correlation and prematurely leap to a conclusion of direct causation.

1. Correlation vs. Causation (Cum Hoc Ergo Propter Hoc)

• The Flaw: Assuming that because two events $A$ and $B$ occur together simultaneously, event $A$ must be causing event $B$.
• Example: "Cities with a high density of ice cream parlors also report high rates of swimming pool drownings. Therefore, eating ice cream causes drownings."
• Reality: A third confounding variable—warm summer weather—induces both higher ice cream consumption and increased swimming activity.

2. Post Hoc Fallacy (Post Hoc Ergo Propter Hoc)

• The Flaw: Inferring a direct causal link based solely on chronological sequence ("Event B happened after Event A, so Event A caused Event B").
• Example: "The university installed new solar panels in March. In April, student enrollment applications increased by 15%. Thus, solar panels attracted prospective students."
• Reality: Ignores seasonal application deadlines, spring marketing campaigns, or regional population shifts.

3. Hasty Generalization

• The Flaw: Drawing a broad, sweeping conclusion about an entire population based on an unrepresentative, skewed, or tiny sample size.
• Example: "Three engineering graduates from University K received top job offers; therefore, University K has the finest engineering curriculum in the nation."

4. Circular Reasoning (Begging the Question)

• The Flaw: Restating the conclusion as a premise using slightly altered vocabulary, without providing genuine independent supporting evidence.
• Example: "Analytical reasoning is the most vital module on the GAT exam because career success depends entirely on analytical aptitude."

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Comparative Strategy Matrix for Argument Evaluation

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Step-by-Step Worked NTS Examples

Worked Example 1: Strengthening an Argument

Passage:

A municipal transportation department installed automated red-light enforcement cameras at 15 major road intersections in City M. Over the following six months, severe traffic collisions at these intersections decreased by 30%. The department concluded that automated red-light cameras effectively improve traffic safety across municipal intersections.

Question: Which of the following, if true, most strongly strengthens the transportation department's conclusion?

• Deconstruction:

  • Premise: Collisions dropped 30% at 15 camera-equipped intersections.
  • Conclusion: Automated cameras effectively improve intersection traffic safety.
  • Target: Find an option that rules out alternative causes or reinforces camera deterrence.

• Option Analysis:

  • Option A: The cost of maintaining the automated camera system exceeded initial budgetary allocations. (Irrelevant to traffic safety impact)
  • Option B: Police traffic enforcement patrols were significantly reduced across all 15 intersections during the same six-month period.
    • Evaluation: If police patrols were reduced, we might have expected collisions to rise. The fact that collisions still dropped by 30% despite fewer police patrols proves the cameras were working even harder to deter reckless driving! This rules out increased police presence as an alternative cause and strongly bolsters the camera effect. (CORRECT - Strengthens)
  • Option C: Drivers in City M reported feeling annoyed by the presence of red-light cameras. (Irrelevant customer sentiment)
  • Option D: Similar camera systems were installed in a neighboring city five years ago. (Lacks specific collision data from that city)

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Worked Example 2: Weakening an Argument

Passage:

A medical study recorded that adults who consumed at least three cups of green tea daily reported 25% lower incidence of cardiovascular illness than adults who consumed no green tea. The lead researcher concluded that specific antioxidants in green tea directly protect against cardiovascular disease.

Question: Which of the following, if true, most seriously weakens the researcher's conclusion?

• Deconstruction:

  • Premise: Green tea drinkers have 25% lower cardiovascular illness.
  • Conclusion: Antioxidants in green tea directly protect against cardiovascular disease.
  • Target: Find an option that introduces a compelling alternative explanation or confounding variable for the lower illness rate among green tea drinkers.

• Option Analysis:

  • Option A: Green tea contains minor amounts of caffeine alongside antioxidants. (Does not explain cardiovascular protection differences)
  • Option B: Adults who routinely drink three cups of green tea daily also engage in significantly more weekly cardiovascular exercise and adhere to healthier low-sodium diets than non-tea drinkers.
    • Evaluation: This introduces a powerful alternative cause! Regular exercise and low-sodium diets directly reduce cardiovascular illness. The lower illness rate among tea drinkers may be driven entirely by their healthier lifestyle habits rather than the antioxidants in green tea! This severely undermines the author's causal claim. (CORRECT - Weakens)
  • Option C: Green tea is grown primarily in mountain regions with high annual rainfall. (Completely irrelevant agricultural background)
  • Option D: Some participants in the study preferred black tea over green tea. (Irrelevant preference detail)