PrepTest 117, Section 2, Question 22
All the evidence so far gathered fits both(42 more words not shown)
The argument above exhibits an(15 more words not shown)
- ADavid and Jane(32 more words not shown)
- BAlthough David thinks(33 more words not shown)
- CDavid and Jane(36 more words not shown)
- DDavid thinks that(36 more words not shown)
- EDavid thinks this(34 more words not shown)
Reading the argument
What if both theories are wrong?
Everything collected so far fits both theories. That means the existing evidence hasn't separated them. It doesn't promise that either theory will survive every future test.
The planned experiment matters because their predictions cannot both be true. Fine: they can't both get this result right. But the author goes further and says the experiment will confirm one theory at the other's expense. That leaves out a result that fits neither prediction. “They can't both be right” allows both to be wrong.
What we’re looking for
For the parallel flaw, look for that same unsupported promise of a winner. We need two competing answers and a test or judgment that's supposed to establish one of them. An answer concluding only that at least one contender is wrong won't make our mistake; it leaves room for both to lose.
Working the answers
- A
Saying at least one person is wrong leaves open the possibility that both are wrong. That's the possibility our original argument overlooks. Here David and Jane disagree, and the conclusion identifies an error on at least one side without promising that the other person's method is correct. Don't let the two people and their disagreement distract from that difference in the conclusion.
- B
This assumes that features consistent with Jane's identification must be inconsistent with David's. But a feature such as having leaves might fit both a beech and an elm. That is a mistake about what a description rules out.
Our original argument already tells us that the predictions cannot both be true. Its mistake comes next: assuming one must be true. B doesn't promise that a future test will validate one of the two opinions. Nor does it actually conclude that Jane has identified the tree correctly.
- C
The conclusion ranks David's ability above Jane's based on one identification. The original doesn't rank the scientists or infer that one is generally better at research. It predicts that the test will vindicate a particular theory. C's jump from a single case to comparative skill is a different jump.
- D
Either there are more beeches than elms, or there aren't. An examination of the whole forest can settle that question. Even a tie would disprove David's claim of more beeches. These alternatives leave no third outcome, unlike two predictions that can both turn out false. D doesn't repeat the flaw.
- ECorrect
David's beech identification and Jane's elm identification match the competing theories. Maria's expert assessment takes the place of the planned experiment. And the conclusion makes the same unsupported promise: Maria will verify one of the opinions.
What if it's an oak? Maria could identify it correctly and show that both David and Jane were wrong. Her expertise doesn't limit the tree to their two guesses, just as running a good experiment doesn't guarantee that one of the two proposed theories is right. The third person is a surface difference; the mistake about the possible outcomes is the same.
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