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Difficulty: MediumRuling Out Alternate Explanations (Defender)

In the 1920s, several textile factories switched their primary power source from steam engines to newly available electric motors. Over the following year, the factories that made this switch reported a substantial drop in the rate of workplace accidents. Based on this record, labor historians concluded that electric motors are inherently safer to operate than steam-powered machinery.

The labor historians' argument depends on which one of the following assumptions?

  1. A
    Textile factories that maintained their steam-powered machinery experienced an increase in workplace accidents during the same period.
  2. B
    Electric motors require less physical exertion and direct interaction from workers than steam-powered machinery does.
  3. The drop in the accident rate was not primarily due to the replaced steam-powered machinery being excessively old and prone to malfunction.Answer
  4. D
    Any manufacturing facility that upgrades its primary power source to a more modern technology will experience a decrease in workplace accidents.
  5. E
    If the textile factories had not switched to electric motors, they would not have experienced any drop in their rate of workplace accidents.

Answer

The option stating that the drop in the accident rate was not primarily due to the replaced steam-powered machinery being excessively old and prone to malfunction.
The argument observes a chronological correlation between a change (switching to electric motors) and an effect (fewer accidents), concluding that the electric motors themselves are inherently safer. For this specific causal conclusion to hold, the argument relies on a defender assumption: it must rule out alternative factors that could have caused the drop in accidents. If the steam machinery being replaced was simply old and deteriorating, then replacing it with any brand-new equipment would have improved safety. Thus, the argument must logically assume that the age and poor condition of the old machinery was not the primary cause of the improved safety record.

Step-by-Step Solution

1
Identify the argument's premises and conclusion.
Premise: Factories saw a drop in accidents after switching from steam to electric power. Conclusion: Electric motors are inherently safer than steam machinery.
Deconstructing the argument is necessary to expose the gap between the evidence provided and the causal claim made.
2
Analyze the causal reasoning and identify potential confounding variables.
The argument assumes that the change in power source caused the safety improvement, ignoring other differences between the old and new setups.
Causal conclusions based on correlational or chronological evidence are vulnerable to alternate explanations.
3
Apply the negation test to the answer choices to find the defender assumption.
Negating the correct option reveals that if the accident drop was actually due to the old machinery being worn out, then replacing it with ANY new machine (even steam) would have reduced accidents. This destroys the claim that electric motors are INHERENTLY safer.
A necessary assumption is one that, if proven false, causes the argument's conclusion to collapse.

Key Concept

Ruling Out Alternate Explanations in Causal Arguments
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Topics

Ruling Out Alternate Explanations (Defender)

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