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Difficulty: HardFlaw in the Reasoning

Economist: A municipal congestion pricing policy will succeed in reducing peak-hour automobile congestion only if the transit authority expands suburban rail capacity. Over the past two years, the transit authority has completed a comprehensive expansion of all suburban rail corridors, and ridership on these commuter lines has doubled. We can therefore conclude that the municipality's newly enacted congestion pricing policy will be successful in reducing peak-hour automobile congestion.

The reasoning in the economist's argument is flawed because the argument

  1. A
    rejects the possibility that expanding suburban rail capacity could fail to attract automobile commuters
  2. B
    disputes the transit authority's data regarding the increase in peak-hour commuter rail ridership
  3. treats a condition that is necessary for the success of a policy as though it were sufficient to guarantee that successAnswer
  4. D
    mistakes an intermediate claim about rail ridership for the argument's final conclusion
  5. E
    presumes that suburban rail expansion is the only measure capable of mitigating urban traffic volume

Answer

The argument is flawed because it treats a condition that is necessary for the success of a policy as though it were sufficient to guarantee that success.
The argument establishes that expanding suburban rail capacity is a necessary requirement for congestion pricing to succeed, introduced by the phrase 'only if'. In the conclusion, the economist infers that because this necessary condition has been satisfied, the policy is guaranteed to succeed. This conflates a necessary condition with a sufficient condition.

Step-by-Step Solution

1
Identify the argument's conclusion and premises.
Conclusion: The newly enacted congestion pricing policy will succeed in reducing congestion. Premise 1: The policy will succeed only if suburban rail capacity is expanded. Premise 2: Suburban rail capacity has been expanded and ridership doubled.
Isolating the structural components of the stimulus is required to assess whether the conclusion logically follows from the premises.
2
Analyze the conditional relationship established in the first premise.
The phrase 'only if' introduces a necessary condition: (Congestion Pricing Succeeds → Rail Capacity Expanded).
Translating conditional indicators accurately determines what is required versus what is sufficient.
3
Evaluate the logical transition from the premises to the conclusion.
The author observes that the necessary condition (Rail Capacity Expanded) is met and erroneously infers that the sufficient condition (Congestion Pricing Succeeds) must also occur.
Satisfying a necessary condition does not guarantee an outcome; doing so commits a classic conditional reversal (confusion of necessary and sufficient conditions).

Key Concept

Distinguishing between necessary and sufficient conditions in deductive reasoning.
Estimated Time:1m 30s
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Topics

Flaw in the Reasoning

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