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Difficulty: EasyNecessary Assumption

Conservationist: The Azure Warbler relies exclusively on the Silver Birch tree for nesting. Over the last decade, a fungal disease has destroyed roughly 30 percent of the Silver Birch trees in the regional park. Because of this significant loss of nesting habitats, the population of Azure Warblers in the park will inevitably decline over the next few years.

Which one of the following is an assumption on which the conservationist's argument depends?

  1. A
    All of the Silver Birch trees that were destroyed by the disease contained Azure Warbler nests.
  2. B
    The regional park contains no other tree species that could be affected by the same fungal disease.
  3. The remaining Silver Birch trees in the park do not provide enough nesting capacity to support the current population of Azure Warblers.Answer
  4. D
    The fungal disease that killed the Silver Birch trees is also directly harmful to the health of the Azure Warblers.
  5. E
    Any decrease in the availability of nesting sites will inevitably lead to a decline in the population of any bird species.

Answer

The correct answer is the option stating that the remaining Silver Birch trees in the park do not provide enough nesting capacity to support the current population of Azure Warblers.
The correct answer identifies the core assumption bridging the gap between the loss of trees and the decline of the bird population. For the argument to hold, it must be true that the park did not previously have a massive surplus of Silver Birch trees. If the remaining 70 percent of the trees are still sufficient to comfortably accommodate all the Azure Warblers, then the population would not inevitably decline. By negating this option ('The remaining trees DO provide enough capacity'), the conclusion is completely undermined, proving this assumption is strictly necessary.

Step-by-Step Solution

1
Identify the core argument's premises and conclusion.
Conclusion: The Azure Warbler population will decline. Premises: Warblers rely exclusively on Silver Birch trees for nesting, and a disease has destroyed 30% of these trees in the park.
Finding the assumption requires understanding exactly what evidence is provided and what claim is being made based on that evidence.
2
Identify the logical gap between the evidence and the conclusion.
The argument assumes that the 30% loss of trees actually creates a shortage. If there were a massive surplus of trees before the disease struck, a 30% drop might not affect the birds' ability to nest at all.
An argument's necessary assumption bridges the gap between the stated evidence and the conclusion by ruling out potential flaws or alternate possibilities.
3
Apply the Negation Test to the potential answers.
Negating the correct option yields: 'The remaining trees DO provide enough nesting capacity.' If this negated statement is true, the conclusion that the population will inevitably decline due to a lack of trees completely falls apart.
The Negation Test is the most reliable way to prove whether an assumption is logically necessary. If negating an option destroys the argument, that option is the correct necessary assumption.

Key Concept

Necessary Assumption and the Negation Test
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Topics

Necessary Assumption

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