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Uncovering Unstated Assumptions

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Read the following excerpt from a municipal transportation committee memo:

'Over the past two years, traffic congestion during peak commuting hours in the city of Apexville has increased by 20 percent, while public bus ridership has declined by 12 percent. During this same period, neighboring Riverdale constructed a multi-line suburban light-rail system, resulting in a 25 percent reduction in commuter highway traffic. To reverse the decline in public transit patronage and alleviate traffic congestion, Apexville should immediately allocate funds to construct a light-rail system identical to Riverdale's.'

What is a critical unstated assumption the author makes regarding the commuters and infrastructure of Apexville compared to Riverdale?

Show answer & explanation

Answer: Apexville and Riverdale have comparable geographic, demographic, and commuting conditions such that Apexville drivers would adopt light-rail at similar rates.; The commuting habits and geographic constraints of Apexville residents are sufficiently similar to those of Riverdale residents.; Apexville commuters will switch to light-rail at the same rate as Riverdale commuters.; Apexville has the financial and spatial infrastructure required to replicate Riverdale's light-rail success.

Answer

The argument relies on the unstated assumption that Apexville and Riverdale share similar geographic layouts, commuter demographics, and travel patterns, guaranteeing that light-rail adoption in Apexville would match Riverdale's outcome.
The argument commits a classic false analogy by assuming that Apexville and Riverdale are sufficiently similar in geography, population distribution, and commuter behavior. Without assuming that Apexville commuters face similar travel vectors and would adopt light-rail at comparable rates, the conclusion that light-rail will solve Apexville's traffic problem remains unsubstantiated.

Step-by-Step Solution

1
Deconstruct the argument's premises and conclusion.
Premises state that Apexville bus ridership fell while congestion rose, and Riverdale built light-rail which reduced highway traffic. Conclusion states Apexville should build a light-rail system to achieve similar results.
Identifying premises and conclusions clarifies where logical leaps occur.
2
Identify the logical gap between the evidence from Riverdale and the recommendation for Apexville.
The author assumes an exact false analogy between the two cities without establishing that Apexville commuters have the same needs or geographic routes as Riverdale commuters.
An unstated assumption is required to bridge the evidence from one context to another.
3
Formulate the necessary underlying assumption.
For the conclusion to hold, Apexville commuters must be willing and able to use light-rail in the same manner as Riverdale commuters, meaning demographic and infrastructure factors must be comparable.
If commuter patterns or geography differ significantly, the light-rail system may fail to reduce traffic or boost transit patronage.

Key Concept

Uncovering Unstated Assumptions
Uncovering Unstated Assumptions Practice Questions — GRE General Test | Examkin