PrepTest 137, Section 3, Question 23
A species in which mutations frequently occur will(35 more words not shown)
The flawed pattern of reasoning(16 more words not shown)
- AIn a stone(34 more words not shown)
- BA play that(40 more words not shown)
- CA person who(38 more words not shown)
- DAn herb garden(36 more words not shown)
- EA diet that(24 more words not shown)
Reading the argument
Having something survival requires doesn't guarantee survival.
Frequent mutations give the species new adaptations in each generation. The other premise says those adaptations are required to survive dramatic environmental changes. But a species could develop new adaptations and still fail to survive: the argument hasn't shown that satisfying this requirement meets every possible challenge.
What we’re looking for
Keep the two relationships separate. Frequent mutations lead to adaptations. Survival also requires adaptations. Sharing that feature doesn't connect frequent mutations to guaranteed survival. For a parallel flaw, look for another argument that reaches a required feature by one route and then treats that feature as enough for a different result.
Working the answers
- A
This follows the requirements in the proper direction. A sturdy wall must be properly built, and a properly built wall has every stone supporting another. So a sturdy wall must have that stone-support feature. It doesn't say having the feature guarantees sturdiness. The conclusion preserves a requirement instead of turning it into a guarantee.
- B
The issue here is the audiences. Not having the same audience every time doesn't mean having a different audience on every occasion. A play could have audience X on Monday, Y on Tuesday, and X again on Wednesday. That would satisfy the second premise without meeting the first premise's condition. This isn't our mistake about treating a shared requirement as a guarantee.
- CCorrect
Perfect honesty leads to telling the truth in every situation, just as frequent mutations lead to new adaptations in every generation. Being morally upright requires that same truthfulness, just as survival requires those adaptations.
Now comes the unsupported jump: a perfectly honest person must therefore be morally upright. Perhaps moral uprightness requires other things besides telling the truth. Perfect honesty meets one requirement without proving the whole status, just as frequent mutation meets the stated survival requirement without guaranteeing survival.
- D
A productive garden requires well-drained soil, and well-drained soil is good soil. Therefore, a productive garden requires good soil. Like A, this carries a requirement through a chain. It doesn't say that any garden in good soil must be productive, which would be a different claim.
- E
A healthful diet must be balanced, and a balanced diet must contain fruits and vegetables. Those premises give a chain of requirements about diets. The conclusion adds a claim about what a person must eat to be healthy. Even if we question that change from a healthful diet to a healthy person, it isn't the original flaw. E never argues that meeting the fruit-and-vegetable requirement guarantees health.
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