Logical reasoning PrepTest 111 · Section 1 · Question 17

Incorrect. The argument here concludes that the "generally" believed position isn't true so this answer runs counter to what the argument does.

Incorrect. This is referring to the climate change and volcanoes. However, they're brought up to show that the theory (Antarctica's ice sheet melted 3m years ago) is possible—they're not meant to be the only possible mechanisms, nor mutually exclusive ones, and the argument doesn't conclude that they are. This answer is therefore incorrect.

Incorrect. The conclusion states that the melting of the ice sheet 3m years ago occurred, not that it was caused by something in particular, so this answer does not correctly describe the argument. Additionally, the argument doesn't reach a determination as to what caused the melt—it just raises two possibilities.

Incorrect. The entire stimulus discusses a single situation, so there's no claim with a "very general application." This answer would be true if the discussion of this one case (Antarctica's ice melting) was used to draw a conclusion about all ice sheets or something to that effect.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Traditional theory — Antarctica has been covered in ice for 14m years
New information — 3m—year—old fossils were found under the ice there
New theory — About 3m years ago, the ice sheet melted temporarily
(This could have happened via climate change or volcanoes)

Answer Anticipation:
This argument attempts to explain a new piece of evidence that cuts against a traditional theory. It falls into a common pattern on the LSAT—phenomenon/explanation. And when that pattern is present, the argument is almost always flawed because it fails to consider alternative explanations.

Here, the conclusion is absolute—the ice sheet "must . . . have" melted. However that's based on two things that "could have" happened. Since the argument fails to establish that it's explanation is definitely correct and it fails to exclude alternative explanations it's flawed. Let's find an answer pointing this out.

Answer Explanation:
The argument here theorizes one explanation for a witnessed phenomenon—the 3m—year—old fossils under the ice in Antarctica. However it never establishes that there aren't other valid theories explaining how they got there and it even notes that its explanation "could have" happened not "must . . . have" as the conclusion states. This argument is thus flawed because it fails to eliminate alternatives as this answer choice states.

Key Takeaway:
If an argument concludes an explanation for a phenomenon it's likely flawed because it fails to consider alternative explanations or fails to rule them out.