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Difficulty: EasyParallel Flaw

Botanist: If a plant species originates in a tropical climate, it requires high humidity to thrive. The newly discovered Silvervine plant does not originate in a tropical climate. Therefore, the Silvervine plant does not require high humidity to thrive.

Which one of the following arguments exhibits a flawed pattern of reasoning most similar to that exhibited by the botanist's argument?

  1. A
    If a dog is a greyhound, it is a fast runner. That dog is a fast runner. Therefore, that dog must be a greyhound.
  2. B
    If a smartphone is heavily used, its battery will degrade quickly. This smartphone's battery has not degraded quickly. Therefore, this smartphone has not been heavily used.
  3. C
    If a plant species requires high humidity, it is difficult to grow indoors. The Silvervine plant is difficult to grow indoors. Therefore, it must require high humidity.
  4. If a vehicle is a commercial airplane, it has wings. This passenger train is not a commercial airplane. Therefore, this passenger train does not have wings.Answer
  5. E
    Every player on the basketball team is an excellent athlete. Therefore, the basketball team as a whole must be an excellent team.

Answer

The argument about the passenger train and wings perfectly mirrors the flawed structure of the botanist's argument.
The original argument exhibits a formal logic flaw known as illegal negation. It establishes a conditional statement (If Tropical -> High Humidity), states that the sufficient condition is not met (Not Tropical), and improperly concludes that the necessary condition is also not met (Therefore, Not High Humidity). The correct argument perfectly mirrors this flawed structure: it sets a rule (If Airplane -> Wings), negates the sufficient condition (Not Airplane), and falsely concludes the negation of the necessary condition (Therefore, Not Wings).

Step-by-Step Solution

1
Identify the logical structure and specific flaw in the botanist's argument.
Premise 1: Tropical -> High Humidity. Premise 2: Not Tropical. Conclusion: Not High Humidity. This is an Illegal Negation.
To find a parallel flaw, you must first precisely abstract the original argument's logical structure.
2
Evaluate the choices to eliminate arguments that use valid reasoning or different types of flaws.
The arguments about the greyhound and the indoor plant commit an Illegal Reversal. The basketball argument is a Part-to-Whole flaw. The smartphone argument is logically valid.
Options with different structural errors or no errors at all are incorrect in a Parallel Flaw question.
3
Match the exact abstract structure (Illegal Negation) to the remaining options.
The argument about the commercial airplane translates to: Airplane -> Wings. Not Airplane. Therefore, Not Wings.
The correct answer must replicate the exact logical pattern (If A -> B; Not A -> Not B) regardless of the subject matter.

Key Concept

Parallel Flaw: Illegal Negation
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Topics

Parallel Flaw

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