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Question

Difficulty: MediumSufficient Assumption

Urban Planner: Any municipal zoning policy that restricts high-density commercial developments within transit corridors inadvertently reduces public transit ridership. Furthermore, no policy that reduces public transit ridership can effectively lower a city's net carbon emissions from passenger vehicles. Therefore, the municipal council's newly enacted downtown zoning policy will not effectively lower the city's net carbon emissions from passenger vehicles.

The conclusion of the urban planner's argument follows logically if which one of the following is assumed?

  1. A
    Any municipal policy that does not effectively lower net carbon emissions from passenger vehicles restricts high-density commercial developments within transit corridors.
  2. B
    The newly enacted downtown zoning policy will affect the overall volume of commercial investment throughout the city.
  3. The municipal council's newly enacted downtown zoning policy restricts high-density commercial developments within transit corridors.Answer
  4. D
    No municipal zoning policy can reduce a city's net carbon emissions unless it completely bans all passenger vehicles from downtown transit corridors.
  5. E
    Increasing public transit ridership is an essential intermediate objective for any municipal council attempting to improve urban livability.

Answer

The municipal council's newly enacted downtown zoning policy restricts high-density commercial developments within transit corridors.
The premises state that restricting high-density commercial developments within transit corridors reduces public transit ridership, and reducing ridership prevents a policy from effectively lowering net carbon emissions (R→D→∼ER \rightarrow D \rightarrow \sim E). The conclusion asserts that the newly enacted downtown zoning policy will not effectively lower net carbon emissions (P→∼EP \rightarrow \sim E). The correct answer provides the exact missing premise—that the new policy restricts high-density commercial developments within transit corridors (P→RP \rightarrow R)—which validly completes the deductive syllogism (P→R→D→∼EP \rightarrow R \rightarrow D \rightarrow \sim E).

Step-by-Step Solution

1
Analyze the premises and map out the conditional chain.
Premise 1 establishes: Restricting transit-corridor commercial development (RR) →\rightarrow Reduces transit ridership (DD). Premise 2 establishes: Reduces transit ridership (DD) →\rightarrow Does not effectively lower net carbon emissions (∼E\sim E). This forms the deductive chain: R→D→∼ER \rightarrow D \rightarrow \sim E, meaning R→∼ER \rightarrow \sim E.
Identifying the formal conditional relationships in the premises isolates what has already been proven.
2
Identify the conclusion and locate the inferential gap.
Conclusion: The newly enacted policy (PP) will not effectively lower net carbon emissions (P→∼EP \rightarrow \sim E). The premises prove that R→∼ER \rightarrow \sim E, but never establish that the new policy (PP) actually restricts transit-corridor commercial development (RR).
A sufficient assumption must provide the exact condition necessary to connect the subject of the conclusion to the chain of premises.
3
Select the assumption that bridges the subject of the conclusion to the initial sufficient condition.
Adding the premise P→RP \rightarrow R completes the chain: P→R→D→∼EP \rightarrow R \rightarrow D \rightarrow \sim E, rendering the conclusion logically necessary.
Connecting the new policy to the restriction condition guarantees that the negative outcome regarding carbon emissions must follow.

Key Concept

Sufficient Assumption (Conditional Chain Completion)
Estimated Time:1m 15s
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Topics

Sufficient Assumption

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