LR Question 12 Explanation
QUESTION TEXT: Paleontologist: Plesiosauromorphs were gigantic…
QUESTION TYPE: Necessary Assumption
CONCLUSION: Plesiosauromorphs probably hunted with long distance chases.
REASONING: Plesiosaurmorphs had long, thin fins. These are like the wings of birds that fly long distances.
ANALYSIS: This is a weak argument. The author has just shown that Plesiosaurmorphs had fins that look like wings. But there are at least two necessary assumptions:
- Because fins look like wings, they serve the same function as wings.
- Because plesiosauromorphs can travel long distances, they hunt over long distances.
___________
- It doesn’t matter why birds and reptiles have similarities.
Negation: Birds and reptiles share features for random reasons that have nothing to do with common ancestors. - It doesn’t matter what kinds of fins other reptiles had. We only care what plesiosauromorphs did with their fins.
- This is a sufficient assumption. We’re looking for a necessary assumption. The negation of this answer doesn’t wreck the argument.
Negation: A gigantic marine mammal might be able to meet its calorie requirements whether or not it hunted over long distances. - “Most” is a terrible choice for necessary assumption answers. Negating from “most” to “half” is almost never significant.
Negation: Only half of marine mammals that chase prey over long distances are specialized for long-distance swimming. - CORRECT. If fin shapes and wing shapes don’t produce the same effects, then the evidence is worthless.
Negation: Fin shape doesn’t affect the way an animal swims in the same way that wing shape affects how birds fly.
Recap: The question begins with “Paleontologist: Plesiosauromorphs were gigantic”. It is a Necessary Assumption question. To practice more Necessary Assumption questions, have a look at the LSAT Questions by Type page.
PT 62, S2, Q12 is supposed to be an Identify the Conclusion question but it’s a Necessary Assumption in the explanations. Is this an error?
Despite how the question stem is worded, it’s actually a Necessary Assumption question. The political scientist’s conclusion actually isn’t stated in the stimulus. If this was a Conclusion question, it would be found in the stimulus.
Looking at the stimulus, you’d notice its structure is like this:
– Some people say xyz
– They’re wrong
– Here’s the reason why they’re wrong
From these three things, you’re basically asked to infer the conclusion. In other words, “if these three things are such, THUS what must necessarily be true?”
Hi! I am a little confused about how to negate C. I thought to negate a conditional statement like C, we would say the sufficient condition does not always lead to the necessary condition. In this case, a gigantic marine mammal might be able to meet its calorie requirements if it “did not” hunt over long distances. I am not sure why Graeme used “whether or not” instead.
To negate answer choices for the purpose of answering necessary assumption questions, you simply need to negate the statement in the most minimal possible sense. So, rather than saying “a gigantic marine animal would be able to find enough food to meet the caloric requirements dictated by its body size if it did not hunt by chasing prey over long distances,” you can say “a gigantic marine animal might be able to.”
It’s a very specific kind of negation, that’s intended to help you determine which of the answer choices would–even when minimally negated–make the argument fall apart in their negated form.
Hi Graeme,
I’m slightly confused about the reasoning for answer D. Generally, as you point out, negating “most” to “half” does not affect the argument.
However, here the conclusion is that “Plesiosauromorphs PROBABLY hunted with long distance chases.” The “probably” makes the conclusion a most statement. So if we say that only half of things with a body-type specialized for long distance swimming hunt at long distances, doesn’t this make the conclusion not “probable” and thus hurt the argument?
I see that (E) is better for the reasons you laid out. Unless I misunderstand (D), though, it seems like it is also a necessary assumption.
Can you elaborate?
JL
Ah, I understand your question better here. The issue with D is that it might not have anything to do with plesiosauromorphs.
“most” only matters on NA questions when the most is DIRECTLY related to the conclusion. Here, the most/half groups could refer to animals other than plesiosauromorphs.
Thanks. That’s pretty clear now. It’s amazing how blind spots can form on some of these answers