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Difficulty: MediumApplying the Negation Technique

City Planner: To alleviate the severe traffic congestion in the downtown area, the city council has proposed implementing a substantial toll for vehicles entering the district during peak hours. This toll will certainly cause a dramatic reduction in the number of private passenger vehicles entering the downtown area during these hours. Therefore, implementing this toll will successfully result in significantly shorter commute times for those individuals who continue to drive into the downtown area.

Which of the following statements are assumptions required by the city planner's argument? Select all that apply.

  1. The reduction in private passenger vehicles will not be entirely offset by an influx of commercial or public transit vehicles entering the downtown area.Answer
  2. B
    Every private passenger vehicle that is deterred by the toll previously contributed to the traffic congestion in the downtown area.
  3. The duration of commutes in the downtown area is not determined exclusively by factors that are completely unaffected by the volume of vehicle traffic.Answer
  4. D
    Drivers who cease entering the downtown area due to the toll will not simply shift their commutes to streets immediately bordering the district.
  5. E
    The primary cause of the current traffic congestion in the downtown area is the volume of private vehicles rather than the volume of commercial trucks.

Answer

The correct statements are the one ensuring the reduction in vehicles is not offset by other types of traffic, and the one stating commute durations are not exclusively determined by factors independent of traffic volume.
Both correct statements are logically required for the city planner's conclusion to hold. If the reduction in private vehicles were entirely offset by an influx of other vehicles, the overall traffic volume would not decrease, preventing shorter commutes. Similarly, if commute times were determined exclusively by factors unaffected by traffic volume, then reducing vehicle volume would have no effect on commute duration. Applying the negation technique to either of these statements logically destroys the author's conclusion.

Step-by-Step Solution

1
Analyze the argument structure to identify the core premise and the main conclusion.
Premise: A toll will dramatically reduce private vehicles entering downtown. Conclusion: This will result in significantly shorter commute times for those who continue to drive downtown.
Isolating the core argument is the essential first step in identifying the logical gap.
2
Identify the logical gap between the premise and the conclusion.
The argument assumes that a reduction in private vehicles directly and successfully translates to shorter commute times, ignoring potential offsetting variables.
Necessary assumptions must bridge this gap or defend the argument against alternative scenarios that would block the conclusion.
3
Apply the negation technique to each candidate option.
Negating the correct options completely destroys the conclusion. Negating the incorrect options leaves the argument logically intact.
The negation technique is the definitive test for validating a necessary assumption.

Key Concept

Applying the Negation Technique to Necessary Assumptions
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Topics

Applying the Negation Technique

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