PrepTest 106, Section 1, Question 21
Psychologist: Some astrologers claim that our horoscopes completely(78 more words not shown)
Which one of the following(9 more words not shown)
- AAstrologers have not(6 more words not shown)
- BThe personality differences(16 more words not shown)
- CThe geographical difference(15 more words not shown)
- DComplete birth records(10 more words not shown)
- EIdentical twins have(9 more words not shown)
Reading the argument
Do these two people actually have the same horoscope?
The psychologist wants to disprove the claim that horoscopes completely determine personalities. A pair of people with the same horoscope but different personalities would be useful evidence. Identical inputs, different results: the horoscope couldn't be doing all the determining.
But the example establishes the same birth date and time, not explicitly the same horoscope. The people were born in different cities. Could location affect the horoscope? Perhaps the relevant position in the sky differs depending on where someone is born. We don't need to know that this is how astrology works. We just need to notice that the argument hasn't ruled it out.
What we’re looking for
For the necessary assumption, I'd look for that missing connection. The psychologist needs the geographical difference not to produce different horoscopes. Otherwise, the different personalities might fit the astrologers' claim perfectly well, and this comparison wouldn't refute it.
Working the answers
- A
The psychologist doesn't need to claim that astrologers have never tested their ideas rigorously. Even a claim that has been studied can face contrary evidence. This argument rests on the comparison between two individuals, not on an absence of previous experimentation.
- B
Cultural differences could explain the different personalities without hurting the psychologist's point. If the people have the same horoscope and culture helps make their personalities different, that would be a reason to reject the idea that the horoscope completely determines personality.
But the psychologist doesn't have to identify culture as the actual explanation either. The argument needs the same-horoscope/different-personality comparison; it doesn't need a complete account of what caused the difference. B unnecessarily rules out one possible explanation.
- CCorrect
Being born in Toronto rather than New York must not give these people different horoscopes. That is the location issue we raised while reading.
Suppose the geographical difference does produce different horoscopes. Then two different personalities wouldn't show that the same horoscope can lead to different results. The astrologers could say the personalities differ because the horoscopes differ. C blocks that response and preserves the comparison the psychologist needs.
- D
We need reliable records for these two people, not a complete record of every birth at both hospitals for forty years. Missing records for other babies wouldn't undermine the stated comparison. D demands far more recordkeeping than this argument uses.
- E
Shared genes or home environments could offer another explanation for similar twins. But the psychologist concedes that twins often have similar personalities and then bases the objection on the two people in different cities. Explaining the twins' similarity isn't required for that objection to work. Even if twins generally had very different home environments, the comparison at the center of this argument would still need the same assumption in C.
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