PrepTest 110, Section 3, Question 9
Lines can be parallel in a Euclidean system(40 more words not shown)
Which one of the following(9 more words not shown)
- AThere are no(14 more words not shown)
- BMost physicists have(22 more words not shown)
- CThere are no(13 more words not shown)
- DThe universe is(21 more words not shown)
- EOnly physicists who(24 more words not shown)
Reading the argument
Why would a different kind of geometry have to lose parallel lines?
We're told that parallel lines can exist in a Euclidean system. That doesn't yet tell us they can't exist anywhere else. Saying the sky can be blue in America doesn't mean it can't be blue in another country. Naming one place where something is possible doesn't make that place exclusive.
The physicists favor a particular non-Euclidean system. Fine, let's suppose they're right about its describing our universe. We still need to know what that system says about parallel lines before concluding that our universe has none. Maybe it allows them too.
What we’re looking for
For the necessary assumption, my first thought is that the author must be treating parallel lines as exclusive to Euclidean geometry. That's the direction of the missing connection I want to investigate. The answer needs to explain why accepting the physicists' system would rule parallel lines out.
Working the answers
- ACorrect
This is more precise than my first prediction. We don't need parallel lines to be exclusive to Euclidean geometry everywhere. We only need them to be absent from this particular non-Euclidean system—the one the physicists regard as describing our universe.
If that system allowed parallel lines, accepting it would give us no reason to conclude that our universe has none. A closes that specific gap without making claims about other systems.
- B
How many physicists have doubted the system isn't the missing connection. Even universal agreement that it describes the universe wouldn't tell us whether it includes parallel lines. The argument needs information about the system's content, not a history of physicists' confidence in it.
- C
This goes too far, much as my initial prediction did. We are discussing one particular system, not every non-Euclidean system with any supporting evidence. Another such system could allow parallel lines without affecting what follows if the physicists' preferred system correctly describes our universe. We don't need to rule parallel lines out of all the others.
- D
The conclusion begins by supposing that these physicists are right. It doesn't need a general rule that prominent physicists must be right whenever they endorse a system. Even with D, we'd still need A's information about whether the system permits parallel lines.
- E
The prominence of the physicists who doubt the system doesn't settle what the system says about parallel lines. The argument is asking what follows if its supporters are right, not whether their opponents are distinguished enough to disagree with them.
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