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Difficulty: HardFlaw in the Reasoning

Botanist: For any plant species to survive in the highly arid dunes of the central desert, it must have a root system capable of reaching deep subterranean aquifers. The newly classified shrub Silene deserta possesses a remarkably extensive taproot system that has been proven to penetrate to the depth of these underground aquifers. Therefore, it is certain that Silene deserta is capable of surviving in the central desert's highly arid dunes.

Which one of the following most accurately describes a flaw in the botanist's reasoning?

  1. A
    fails to consider that the absolute depth of a plant's taproot may not perfectly correspond to the percentage of total water it can successfully absorb
  2. B
    infers that a plant as a whole can withstand a harsh environment purely on the basis that one of its specific biological structures is uniquely adapted to that environment
  3. takes a condition that is required for a plant species to survive in a particular environment to be a condition that ensures its survival in that environmentAnswer
  4. D
    concludes that the depth of a plant's root system causes its survival without considering whether the two phenomena are merely correlated by a third factor
  5. E
    illicitly relies on two different meanings of the concept of survival between the established premise and the final conclusion

Answer

The correct answer is the option stating that the argument takes a condition that is required for a plant species to survive to be a condition that ensures its survival.
The correct answer accurately identifies an illegal reversal of conditional logic. The first sentence establishes that reaching deep subterranean aquifers is a necessary condition for survival ('must have'). The argument then shows that Silene deserta meets this necessary condition, and concludes that its survival is therefore guaranteed. This illicitly treats a required condition as a sufficient one, failing to consider that there may be other necessary conditions for survival.

Step-by-Step Solution

1
Identify the main conclusion of the argument.
The conclusion is the final sentence: 'Therefore, it is certain that Silene deserta is capable of surviving in the central desert's highly arid dunes.'
This is the primary claim the botanist is attempting to prove, explicitly signaled by the word 'Therefore'.
2
Map the conditional logic established in the premises.
Premise 1 establishes a rule: If a plant survives in the central desert -> It must reach deep aquifers. Premise 2 provides a fact: Silene deserta reaches deep aquifers.
Formalizing the logic reveals the structural relationship between the evidence and the conclusion. 'Must have' introduces a necessary condition.
3
Evaluate how the premises are used to reach the conclusion.
The argument observes that the necessary condition (reaching aquifers) is met, and concludes that the sufficient condition (survival) will definitely occur.
This is a formal logical fallacy. Meeting one requirement for an outcome does not guarantee the outcome, because there may be other unstated requirements (e.g., resisting extreme temperatures).

Key Concept

Flaw in the Reasoning - Confusing Necessary and Sufficient Conditions
Estimated Time:2m 0s
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Topics

Flaw in the Reasoning

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