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Difficulty: EasyNecessary Assumption

A university library recently replaced all of its older fluorescent ceiling lights with energy-efficient LED fixtures that emit a cooler, bluer spectrum of light. During the semester following the installation, the average number of hours students spent studying in the library each evening increased by thirty percent. The university administration concluded that the cooler light spectrum provided by the LED fixtures directly caused students to study for longer periods. Which one of the following is an assumption on which the university administration's argument depends?

  1. A
    Installing LED fixtures is the most effective method available to university administrators for increasing student study time.
  2. B
    Students who study under fluorescent lighting always experience greater eye fatigue than those who study under LED lighting.
  3. The increase in average evening study hours was not primarily the result of other changes made to the library during the same semester.Answer
  4. D
    If the university had retained the fluorescent lighting, the average number of evening study hours would have substantially decreased.
  5. E
    Prior to the replacement, students had formally submitted complaints to the university regarding the quality of the fluorescent lights.

Answer

The argument depends on the assumption that the increase in average evening study hours was not primarily the result of other changes made to the library during the same semester.
The author infers a direct causal relationship from a chronological correlation (new lighting followed by longer study hours). For this causal conclusion to hold, the author must assume that other concurrent factors (such as extended facility hours, new tutoring programs, or changes in academic policies) were not the true primary cause of the increase. Logically negating this statement confirms that if other changes caused the increase, the administration's argument collapses.

Step-by-Step Solution

1
Identify the core premises and the conclusion
Premises: Fluorescent lights were replaced by cooler-spectrum LED fixtures, and subsequent average evening study hours rose by 30%. Conclusion: The cooler light spectrum directly caused the increase in study time.
Isolating the conclusion clarifies the specific causal leap made by the author.
2
Detect the unstated assumption bridging the premises to the conclusion
The author assumes that no confounding variable or alternative factor introduced during that same semester was responsible for the increase in study hours.
Causal conclusions always require ruling out plausible alternative causes that could fully account for the observed correlation.
3
Apply the Negation Test to verify necessity
Negating the statement gives: 'The increase in study hours WAS primarily the result of other changes made to the library during the same semester.' This directly shatters the conclusion that the lighting caused the increase.
A necessary assumption must fatally undermine the conclusion when logically negated.

Key Concept

Necessary Assumption: Defender Pattern (Ruling out alternative explanations for a causal conclusion)
Estimated Time:55s
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Necessary Assumption

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