PrepTest 134, Section 2, Question 16
Anyone who believes in extraterrestrials believes in UFOs.(18 more words not shown)
Which one of the following(12 more words not shown)
- AAnyone who believes(21 more words not shown)
- BAnyone who believes(20 more words not shown)
- CAnyone who believes(20 more words not shown)
- DAnyone who believes(24 more words not shown)
- EAnyone who believes(29 more words not shown)
Reading the argument
People can hold two beliefs together and be wrong about only one of them.
Let's accept the stated rule: anyone who believes in extraterrestrials also believes in UFOs. That describes what the believers think. It doesn't establish that extraterrestrials can exist only if UFOs exist. Aliens could exist somewhere without the UFOs these people believe in being real.
So disproving UFOs doesn't disprove extraterrestrials. The argument treats a connection between people's beliefs as a connection between the truth of those beliefs.
What we’re looking for
For the parallel flaw, keep the order straight. Belief in the first thing brings belief in the second. The second thing is then disproved, and the author concludes that the first thing doesn't exist either. We need that same move, including which of the two things gets disproved.
Working the answers
- ACorrect
Unicorns take the role of extraterrestrials; centaurs take the role of UFOs. Everyone who believes in the first also believes in the second. Centaurs, the second thing, are then shown not to exist, and the conclusion denies unicorns, the first thing.
That is the same mistake. People who believe in unicorns could mistakenly believe in centaurs without their unicorn belief also being false. Linking the beliefs doesn't make the existence of one creature depend on the existence of the other.
- B
This stays entirely with what a person believes. If every unicorn believer believes in centaurs, a person who doesn't believe in centaurs cannot be a unicorn believer. Otherwise that person would violate the given rule. B makes a valid inference about the person's beliefs; it doesn't jump from disproving a creature's existence to disproving another creature.
- C
Not believing in unicorns doesn't tell us whether you believe in centaurs. The rule tells us what unicorn believers believe, not what everyone else believes. C makes a mistake about the direction of the belief relationship, but neither of its last two claims concerns whether the creatures actually exist. That differs from our belief-to-truth mistake.
- D
Having no good reason to believe something isn't the same as conclusively disproving it. D starts with a lack of justification for the centaur belief and extends that lack of justification to the unicorn belief. The original goes further: it treats the second thing's nonexistence as establishing the first thing's nonexistence.
- E
This switches the roles in the second half. It disproves unicorns, the first thing, then rejects belief in centaurs, the second. The original disproves UFOs, the second thing, then rejects extraterrestrials, the first. Because the initial belief relationship runs only one way, those roles aren't interchangeable. E shares the broad mistake of linking truth to shared belief, but A matches the actual direction too.
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