PrepTest 135, Section 1, Question 11
Inspector: The only fingerprints on the premises are(18 more words not shown)
Which one of the following(14 more words not shown)
- AThe campers at(31 more words not shown)
- BThe second prototype(30 more words not shown)
- CEach of the(19 more words not shown)
- DAll of Marjorie's(22 more words not shown)
- EAll of these(27 more words not shown)
Reading the argument
What if Mr. Tannisch took the diamonds?
His fingerprints are the only ones found, yet the inspector jumps to an explanation for why the culprit left no fingerprints: the culprit wore gloves. That skips an obvious possibility. The person with the diamonds might be the very person whose prints are present.
There are other possibilities too. Someone might have avoided touching surfaces that would preserve prints, or wiped the prints away afterward. Finding no other prints doesn't prove nobody else touched anything. But for a parallel flaw, the most distinctive problem is treating the one identified source of the evidence as though it has already been cleared of suspicion.
What we’re looking for
Look for an argument that identifies one possible source, then concludes the cause must lie elsewhere without ruling that source out. We don't need another crime story. We need that same unjustified exclusion.
Working the answers
- ACorrect
The campers have eaten food only from the camp cafeteria. Why couldn't that food have made them sick? The argument treats the cafeteria as though it has already been ruled out, just as the inspector treats Mr. Tannisch as though he couldn't have taken the diamonds.
The cafeteria is the one identified food source; Tannisch is the one identified source of fingerprints. In each case, identifying that source doesn't establish its innocence. The argument's conclusion requires a reason to dismiss it, and no such reason is given.
- B
The second prototype performed worse, so the author suggests its production might have differed from the first one's design. This offers a possible explanation for a difference in performance. It doesn't identify one source and then exclude that source as a possible cause. Also, its tentative “might” is unlike the inspector's insistence that gloves must have been worn.
- C
Each swimmer's history of losing doesn't establish that nobody at this meet is likely to win. Someone can win against competitors who also usually lose. This moves from individual records to a prediction about the whole field; it doesn't wrongly clear the one source identified by the evidence.
- D
Perhaps Marjorie brushes the right side more carefully, rather than chewing more on the left. The location of the cavities doesn't establish the proposed cause. That is an unsupported causal explanation, but its structure differs from excluding Tannisch: D never identifies a particular possible culprit and then treats that culprit as innocent.
- E
Tomato plants growing larger doesn't establish that pea plants will grow in the same way. The argument transfers a result from one kind of plant to another. Our inspector isn't making a prediction by comparing two kinds of things; the inspector overlooks a possible culprit already present in the evidence.
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