Logical reasoning PrepTest 110 · Section 3 · Question 9

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Assumption

Stimulus Summary:
Euclidean geometry — Lines can be parallel
Non—Euclidean geometry — Some prominent physicists thinks this describes the universe
Conclusion — Lines can't be parallel

Answer Anticipation:
The argument establishes that parallel lines exist in Euclidean geometry. It then goes on to say that certain physicists believe Euclidean geometry doesn't describe our universe—rather, non—Euclidean geometry does. From this, it concludes—if the physicists are correct—that there aren't parallel lines.

First, note the qualification on the conclusion—"If these physicists are right." When a conclusion is based on a viewpoint the argument does assume that viewpoint is right. By qualifying the conclusion however this answer doesn't make that assumption—it predicates the conclusion on it being true. So we have to look elsewhere for the assumption.

Why does the author believe that the universe has no parallel lines? The physicists she relies on don't discuss them at all! Rather it's because they believe non—Euclidean geometry describes the universe and Euclidean geometry has parallel lines. But just because Euclidean geometry has parallel lines doesn't mean non—Euclidean geometry lacks them—they could both have parallel lines. Tall people eat food—that doesn't mean non—tall people don't. Let's find an answer establishing that the non—Euclidean geometry system discussed in the stimulus lacks parallel lines.

Answer Explanation:
We get the right answer right off the bat! The argument assumed that the non—Euclidean system that some prominent physicists believe describes the universe correctly lacks parallel lines. If there are parallel lines in that system then the conclusion falls apart as the physicists being right would guarantee that the universe does have parallel lines.

Key Takeaway:
Always note qualified conclusions—they generally serve to remove a potential avenue for answers. Whatever the conclusion is conditioned on isn't being assumed. Noting it here was what allowed us to quickly eliminate three incorrect answers!

Incorrect. What matters is if the physicists are correct, not whether most physicists agree with that view.

Incorrect. This answer is too broad. The argument requires assuming that there are no parallel lines in one specific non—Euclidean geometry system—the one that physicists believe correctly describes the universe—not "every" non—Euclidean system that has empirical evidence.

Incorrect. The conclusion is already conditioned on these physicists being correct, so the argument doesn't need this assumption.

Incorrect. Who agrees or disagrees with the view of the prominent physicists is immaterial to the reality of the universe or the correctness of their view—especially since the conclusion is conditioned on that view being correct.