PrepTest 103, Section 3, Question 10
Tires may be either underinflated, overinflated, or neither.(31 more words not shown)
Which one of the following(9 more words not shown)
- AThe argument assumes(6 more words not shown)
- BThe argument overlooks(12 more words not shown)
- CThe argument fails(12 more words not shown)
- DThe argument rejects(11 more words not shown)
- EThe argument fails(8 more words not shown)
Reading the argument
That conclusion sounds familiar, but look at the reason offered for it. The author says too little or too much air harms tire tread because nobody has shown that it doesn't. We aren't given a test showing damage or a comparison of tire wear. We are given a failure to prove the opposite.
Try the same reasoning with a less familiar claim: nobody has shown that there are no unicorns on Mars, so there must be unicorns on Mars. The lack of a disproof hasn't supplied evidence that the unicorns exist.
What we’re looking for
The flaw question asks us to identify that same jump here. We don't need to decide what really happens to tires at different pressures. The issue is whether failing to establish that they aren't harmed lets us conclude that they are.
Working the answers
- A
The premise and conclusion aren't the same claim. “Nobody has shown that these conditions are harmless” is different from “These conditions are harmful.” Moving between them is the error, but the argument doesn't simply repeat its conclusion as evidence for itself.
- B
“Not in principle susceptible to proof” means incapable of being proved, even in theory. That is different from something that nobody has proved yet. The passage reports the latter; it doesn't establish that evidence about tire damage is impossible to obtain. B can sound close because it mentions proof, but it introduces a limit the argument never gives us.
- C
The missing support is more basic than an explanation of the physical mechanism. Good evidence of increased wear could support a harm claim even without a complete account of how the damage happens. Here, the author substitutes the absence of a disproof for evidence of harm. C doesn't identify that substitution.
- DCorrect
The unproved possibility is that underinflation and overinflation do not harm tire tread. That possibility could still be true even though nobody has established it. The author dismisses it and accepts harm just because harmlessness hasn't been proved.
Return to the unicorn example: not having established “no unicorns” doesn't make “unicorns” true. Likewise, not having established “no harm” doesn't make “harm” true. D describes exactly that failure to leave the unproved possibility open.
- E
We understand underinflation and overinflation as too little and too much inflation. Precise numerical thresholds wouldn't repair the move from no proof of harmlessness to a conclusion of harm. The reasoning would still need evidence for its conclusion even with perfectly defined terms.
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