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Difficulty: HardIdentifying Necessary Assumptions

Policy Analyst: To combat congestion, the city of Oakhaven recently implemented a $10 toll for private vehicles entering the downtown business district during morning rush hour. Last month, which was the first month of the toll, the number of private vehicles entering the district during morning rush hour dropped by 30% compared to the previous month. Therefore, the financial cost of the toll must be what deterred these drivers from entering the district during morning rush hour.

Which of the following are necessary assumptions required by the policy analyst's argument?

  1. The 30% reduction in morning rush hour traffic was not primarily caused by a concurrent, unrelated disruption to the main access routes into the downtown district.Answer
  2. B
    A $10 daily fee is a severe enough financial penalty to force any commuter to seek alternative routes or methods of transportation.
  3. C
    Oakhaven's public transit infrastructure was expanded adequately to accommodate the influx of commuters who opted not to drive.
  4. A significant portion of the drivers who ceased commuting into the district during morning rush hour were not shielded from the toll's financial impact by employer reimbursements.Answer
  5. E
    The implementation of the toll did not cause a proportional increase in traffic on the residential streets immediately surrounding the downtown district.

Answer

The argument fundamentally requires ruling out alternative causes for the traffic decrease and establishing that the drivers who stopped driving actually experienced the financial burden.
To validly conclude that the financial cost of the toll directly caused the 30% drop in traffic, the argument depends on two key elements. First, it must assume that no other major event (like a sudden road closure) caused the drop instead. Second, it relies on the mechanism of 'financial cost' acting as a deterrent; this requires assuming that the drivers who stopped actually faced that cost, rather than having it entirely subsidized by their employers. Both of these statements pass the Negation Test: if either is negated, the analyst's causal conclusion completely collapses.

Step-by-Step Solution

1
Identify the core argument.
Premise: Toll implemented -> Traffic dropped 30%. Conclusion: The financial cost of the toll caused the drop.
Deconstructing the argument reveals a causal claim based on a sequence of events.
2
Identify vulnerabilities in the causal claim.
The argument assumes no other event caused the drop (correlation vs. causation) and assumes the drivers actually felt the financial cost of the toll.
Necessary assumptions in causal arguments typically defend against alternative causes or bridge the gap between the mechanism (cost) and the result (deterrence).
3
Apply the Negation Technique to the plausible options.
Negating the option about route disruptions provides an alternative cause, destroying the argument. Negating the option about employer reimbursements removes the financial cost from the drivers, also destroying the argument.
The Negation Technique is the definitive test for necessary assumptions: if the logical opposite of a choice makes the conclusion impossible, the choice is necessarily assumed.

Key Concept

Identifying necessary assumptions in causal arguments requires either a 'Defender' assumption (ruling out alternative causes) or a 'Supporter' assumption (connecting the premise's mechanism to the conclusion).
Estimated Time:2m 0s
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Identifying Necessary Assumptions

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