Argument Structure Questions - - Question 21

Joseph:  My encyclopedia says that the mathematician Pierre de Fermat died in 1665 without leaving behind any written...

Arthur-Guerra October 23, 2019

Why not answer A?

I narrowed it down to answers A and B. I understand the concept of a subsidiary conclusion, but I do not see how "this alleged theorem simply cannot be proved" feeds into the main conclusion. I find no evidence to support the "subsidiary" conclusion, which is what makes it hard. When are you supposed to infer and not infer; because many of the questions at hand expect you to infer certain things, but also expect you to not infer others.

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SamA October 23, 2019

Hello @Arthur-Guerra,

Rather than make inferences, let's start by breaking down Joseph's argument. In order to identify premises, sub-conclusions, and main conclusions, we have to pay close attention to the structure of the argument. I like to think of it in terms of questions and answers. That lets me know which statements support which.

Conclusion: Therefore it is likely that Fermat was either lying or mistaken.
Why?
Sub-conclusion: Because this theorem probably cannot be proven.
Why?
Premise: Because no one else has been able to prove it.

A is incorrect because Joseph does offer support for this statement. It may be flawed support, but he offered support nonetheless. You can tell because of the word "since." We do not need to guess about Joseph's reasoning, because the language he uses directs us from support to conclusion.

Do you see why the primary conclusion is based on this sub-conclusion? If the theory is probably unprovable, them Fermat probably didn't prove it. Answer choice A successfully tracks Joseph's argument.

Arthur-Guerra October 24, 2019

Hi,

I see the primary conclusion is based on the sub-conclusion now.

Yes, the breakdown was extremely helpful, and something I will probably employ during the practice questions, etc., so I can become more familiar with I.D. the structure of the arguments.

Thank you!

theprince5 February 29, 2020

This is how I broke it down:

Joseph Conclusion:
it is likely that Fermat was either lying or else mistaken when he made his claim.

Premise:
Fermat died in 1665 without leaving behind any written proof for a theorem that he claimed nonetheless to have proved.

Premise (Subsidiary conclusion)

this alleged theorem simply cannot be proved

Premise (of Subsidiary conclusion)

since—as the article points out—no one else has been able to prove it.

Laura Conclusion

your claim—that Fermat was lying or mistaken—clearly is wrong.

Premise number one (subsidiary conclusion):

Your encyclopedia is out of date
Premise of (Subsidiary conclusion)

Recently someone has in fact proved Fermat's theorem

Premise number two

And since the theorem is provable