I saw this on some LSAT prep book:

Question: for example in a mistake necessary as sufficient question,

Premise: If A then B.

Conclusion: B therefore A.

Given two answer choices

  • If A then B, and if B then C.
  • C, therefore A.

  • if A then B, not A, therefore not B.
  • Should we choose the one with additional premise or the one with contrapositive conclusion?

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    5 comments

    • Wednesday, Nov 03 2021

      def the match. additionally, answer choice 2 would actually be a mistaken negation- confusing the sufficient for necessary

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    • Thursday, Oct 28 2021

      Yeah whatever is the match!

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    • Thursday, Oct 28 2021

      No problem! :)

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    • Friday, Oct 22 2021

      Thank you!! Yes, I've seem both happened to be correct in the past. This is actually from The LSAT Trainer, and Mike Kim chose 1) as well. > @rochishatogare811 said:

      I feel like this is risky enough (with students complaining that both answers are right) that LSAC wouldn't give both in the same question unless the stimulus matched one exactly. But if I had to pick I'd lean towards (1). In the end A --> B, B--> C is just A --> C. If we then erroneously say C, therefore A, it's generally the same as the stimulus since we're affirming the necessary condition in both cases.

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    • Thursday, Oct 21 2021

      I feel like this is risky enough (with students complaining that both answers are right) that LSAC wouldn't give both in the same question unless the stimulus matched one exactly. But if I had to pick I'd lean towards (1). In the end A --> B, B--> C is just A --> C. If we then erroneously say C, therefore A, it's generally the same as the stimulus since we're affirming the necessary condition in both cases.

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