QUESTION TEXT: Joan got A's on all her homework…
QUESTION TYPE: Flawed Reasoning
CONCLUSION: Joan will have to do the class presentation to pass.
REASONING: If she had gotten an A on her paper, she could have passed even without the presentation. But Joan didn’t get an A on the paper.
ANALYSIS: This is an incorrect negation. We had: Get an A ➞ Doesn’t need presentation.
The argument incorrectly switches this to:
A ➞ Does need presentation.
But it’s possible Joan wouldn’t need to do the presentation even though she didn’t get an A on her paper. Joan might otherwise have had excellent grades, and a B+ on the paper.
- Actually, the argument did consider this possibility: but it’s a mistake! It doesn’t have to be the case that Joan needed one or the other.
- CORRECT. We have nothing to tell us that not getting an A is a sufficient condition for having to do the class presentation.
- The argument wasn’t concerned with the overall grade. It only considered whether or not Joan could pass.
- This is the same thing as A. The argument didn’t ignore this possibility: it assumes that this is true, but it has no evidence for the claim.
- Other students are irrelevant. This is only about Joan.
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