Exam LSAT Section 1 Logical Reasoning topic 1 question 180 discussion

Actual exam question from Test Prep's LSAT Section 1 Logical Reasoning

Question #: 180
Topic #: 1

[All LSAT Section 1 Logical Reasoning Questions]

Joseph: My encyclopedia says that the mathematician Pierre de Fermat died in 1665 without leaving behind any written proof for a theorem that he claimed nonetheless to have proved. Probably this alleged theorem simply cannot be proved, sinceas the article points outno one else has been able to prove it.
Therefore, it is likely that Fermat was either lying or else mistaken when he made his claim.
Laura: Your encyclopedia is out of date. Recently someone has in fact proved Fermat's theorem. And since the theorem is provable, your claimthat Fermat was lying or mistakenclearly is wrong.
Which one of the following most accurately describes a reasoning error in Laura's argument?

A. It purports to establish its conclusion by making aclaim that, if true, would actually contradict that conclusion.
B. It mistakenly assumes that the quality of a person's character can legitimately be taken to guarantee the accuracy of the claims that person has made.
C. It mistakes something that is necessary for its conclusion to follow for something that ensures that the conclusion follows.
D. It uses the term "provable" without defining it.
E. It fails to distinguish between a true claim that has mistakenly been believed to be false and a false claim that has mistakenly been believed to be true.

Show Suggested Answer

Suggested Answer: C 🗳️
Lauras evidence is that someone has proved the theorem, and her conclusion is that Fermat was not lying nor mistaken. She assumes that because the theorem has now been proven, Fermat must have also proved it. For her conclusion to be correct that Fermat was not lying or mistaken, it is necessary that the theorem be proved, but the fact that someone has proved the theorem isnt sufficient to make her case. With all due respect to Fermat, the fact that someone else has proved the theorem does not necessarily mean that Fermat has. Choice C. identifies the necessary/sufficient flaw in Lauras argument.

by [deleted] at March 9, 2025, 1:31 p.m.

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