PrepTest 139, Section 4, Question 17
Because no other theory has been able to(70 more words not shown)
Which one of the following(10 more words not shown)
- AUnless a phenomenon(26 more words not shown)
- BA phenomenon that(26 more words not shown)
- CUnless a theory(25 more words not shown)
- DIf a theory(27 more words not shown)
- EIf a theory(30 more words not shown)
Reading the argument
Knowing the result you want to explain doesn't automatically make your explanation worthless.
Set aside the unfamiliar astronomy for a moment. We have a phenomenon involving Mercury, and Einstein's theory accounts for it simply and accurately. People use that match as evidence for the theory. The author objects that the phenomenon was already known and Einstein probably adjusted his equations to fit it.
I can see the concern about building a result into a theory and then using that same result to support it. But working backward isn't automatically invalid. A writer can plan a story's ending before writing the earlier chapters; that doesn't by itself make the completed story incoherent. Similarly, an equation developed with a known phenomenon in mind could still describe it accurately. We need a reason that this particular fit cannot count as support.
What we’re looking for
The task is to help justify the author's conclusion. So look for a principle saying that when a theory is specifically adjusted to match a phenomenon, that match shouldn't count as evidence for the theory. Notice the limit: we're excluding one piece of proposed evidence, not declaring the whole theory false.
Working the answers
- A
This concerns credit for discovering a phenomenon. Nobody claims Einstein discovered the advance of Mercury's perihelion; the passage says it was already known. A theory could fail to deserve discovery credit while its explanation of the phenomenon still counted as support. A doesn't supply the rule about evidence that we need.
- B
This requires having the phenomenon in mind before the match can count as evidence. The passage already suggests that Einstein did have it in mind. Meeting that requirement leaves open whether the match should count; B doesn't say that it must count, and it doesn't give us a reason to exclude it. The author needs a rule making the deliberate adjustment a reason against using this evidence.
- C
We aren't told that the theory fails to account for some other relevant, previously known phenomenon. Without such a failure, this requirement doesn't undermine the theory's support. It also doesn't explain why successfully accounting for this one phenomenon should be excluded as evidence.
- DCorrect
This directly connects the alleged adjustment to the conclusion. If Einstein adjusted the theory specifically to fit the phenomenon, then the resulting match should not count as evidence in its favor. The principle makes the author's stated concern relevant in exactly the way the argument needs.
- E
This is close until the final claim. It says the theory shouldn't be credited with predicting a phenomenon that was already known and built into it. But our conclusion concerns whether the match supports the theory. Something might not qualify as a prediction and still be relevant evidence. E changes the question from evidential support to what deserves the label “prediction.”
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