Joseph: My encyclopedia says that the mathematician Pierre

(A) It purports to establish its conclusion by making a claim that, if true, would actually contradict that conclusion.
-- Laura's claim to establish the conclusion is not at all contradicting with the conclusion she wants to establish. Hence A cannot be a correct answer choice.

(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.
She is nowhere trying to use quality of person's character to guarantee her claim. Hence B cannot be a correct answer choice.

(C) It mistakes something that is necessary for its conclusion to follow for something that ensures that the conclusion follows.
-- Laura is trying to ensure that her conclusion follows by stating that is required for the conclusion to be true. Hence C is a correct answer choice.

(D) It uses the term “provable” without defining it.
-- This is irrelevant. Hence D cannot be a correct answer choice.

(E) It fails to distinguish between a true claim that has mistakenly between believed to be false and a false claim that has mistakenly been believed to be true.
[color=#FF0000]-- There are no two claims. Hence E is not a correct answer choice.[/color]
Thank You.

Thanks,
Akhil M.Parekh

I narrowed to C and E but still cannot understand why C is correct.

Joseph Perrie no written proof +
! others proof ---> lying

laura proof ----> !lying

proof is not a necessary condition in Joseph's argument.

C brings out this exact reasoning.

Good question.

what is the source of this question?

I have the the same problem;

these are some incredibly wordy answer choices; nothing like what I've seen on GMAT prep 2014. Will questions like this be on the GMAT?

i agree ~ but there's a reason for that: As you notice, there's a whole lot of mid-range level Qs on that software.

Those are the questions that deserve the most attention. Ace those questions, and don't fuss too much over the tough ones.

Honestly, only if you're doing really well --- hovering around the 90%-tile range ~ You'll see alot of those convoluted-wordy questions.
Or, sometimes near the beginning, as the CAT is adjusting to your skill level.

If you see this problem, you should:
1) Pat urself on the back b/c ur doing really well
2) Don't worry! Even if you see this near the beginning of the test, don't sweat it. It's not worth alot nor the stress.

But, definitely practice the tough ones ~ as they'll make the "lower leveled ones" even easier.

Would you please help me to figure out the followings?

C. It mistakes something that is necessary (what is necessary?) for its conclusion (what is conclusion?) to follow for something (what is this something?) that ensures that the conclusion follows.

Thanks , your explanations clarifies the OA. But it will be difficult to understand for those members who doesn't have an idea about the relation between necessary condition and sufficient condition.

Could you please make a post explaining about those.

It's funny, we're working on a Topic of the Week on the distinction between necessary and sufficient. There are a few topics in line ahead of it, but we'll get to it.

And in the meantime, there are a couple of pretty good explanations of the issue here: https://gmatclub.com/forum/a-sufficient ... 50740.html

I hope this helps!

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, since---as the article points out---no 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 claim---that Fermat was lying or mistaken---clearly 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 a claim 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.

Laura's argument says what is necessary for its conclusion to follow. But, her argument DOES NOT ensure that the conclusion follows, because even if the the theorem is provable, there is no mention whether Fermat has proved it or not. So, still the fact that - "Fermat was lying or...." can be true.

Hence C is right.

(D) It uses the term “provable” without defining it.

(E) It fails to distinguish between a true claim that has mistakenly between believed to be false and a false claim that has mistakenly been believed to be true.

Tough one to crack. Nice explanation by AbhayPrasanna and GMATninja...

Simple passage, but really tough alternatives!

Conufsed between B and C.

"It mistakes something that is necessary for its conclusion to follow for something that ensures that the conclusion follows."

Not able to understand what is necessary for conlcusion and what is ensures the conclusion??

GMATNinja I read your post but could you please explain in more detail. I am always confused between necessary and sufficient.

And why is option B wrong?? I didn't understand the meaning of option B. Is it talking about the quality of laura or the person who proved it..

Based on Laura's statements, we now KNOW that Fermat’s theorem is provable. But does that mean that Fermat himself proved the theorem? In order for it to be true that Fermat himself proved the theorem, the theorem MUST be provable (it would be impossible to prove a theorem that is not provable!).

If the theorem is not provable, then we definitely cannot conclude that Fermat himself proved the theorem (and, thus, that he was not lying or mistaken).


The claims discussed in this passage are those made by Fermat. Specifically, Fermat claimed that he proved the theorem. So (B) must be referring to the accuracy of Fermat's claim.

So does Laura "mistakenly assume that the quality of [Fermat's] character can legitimately be taken to guarantee the accuracy of the claims that [Fermat] has made"? In other words, does Laura conclude that Fermat was not lying because of his personal qualities (i.e. how trustworthy/honest he is)? No, this does not accurately describe Laura's logic, so (B) should be eliminated.

I hope that helps!

GMATNinja

Can help me in eliminating Ans Choice A- It purports to establish its conclusion by making a claim that, if true, would actually contradict that conclusion.?
- My understanding of A is -
A claim if true -Laura claimed that since theoram is provable Would actually contradict That conclusion- joseph's conclusion will be contradicted?
isn't this the flaw in Laura's reasoning? Because, if true, this doesn't necessarily contradict Joseph's conclusion.

Joseph claims that Fermat was lying or mistaken when he said he proved his theorem. Laura concludes that Joseph's claim is wrong. To reach this conclusion, Laura points out that Fermat's theorem is provable, since someone recently proved it. The correct answer should describe an error in Laura's argument.

Let's now consider (A):


Let's start by identifying Laura's conclusion and her claim.

• Laura's conclusion: the idea that Fermat was either lying or mistaken is wrong (i.e. Fermat was NOT lying or mistaken).
• Laura's claim: Fermat's theorem is provable.

So does her claim contradict the conclusion? In other words, does the fact that Fermat's theorem is provable contradict the idea that Fermat was NOT either lying or mistaken? Or put another way, does the fact that Fermat's theorem is provable mean that Fermat was lying or mistaken?

Well, Fermat claimed that he proved his theorem. Does the fact that his theorem was provable mean that he was lying or mistaken? Not at all. Just because his theorem is provable doesn't mean that he was lying or mistaken when he claimed to have proved it.

In fact, the idea that Fermat's theorem is provable actually supports the idea that Fermat might have proven his theorem. Because if the theorem is provable, then maybe he did prove it? (Whereas if it isn't provable, he definitely didn't prove it). So if anything, Laura's claim actually supports her conclusion.

Bottom line, the claim that Fermat's theorem is provable doesn't support the idea that he was lying or mistaken about having proved it. So it doesn't contradict the idea that Fermat was NOT lying or mistaken. And because Laura's claim doesn't contradict her conclusion, we can eliminate (A).

I hope that helps!

It took me a while to even understand what E was saying. It is basically a bunch of mumbo-jumbo (nonsense). I still do not understand fully what it means and don't know if there is any context where option E would be the right choice. However, in this example, it is the wrong option as the conditions of it are not fulfilled. While Laura's argument does include a true claim that was previously thought to be wrong, it does not include a false claim that is actually true. We simply don't know whether or not Fermat was wrong or lying. Therefore, option C is correct.