QUESTION TEXT: Roberta is irritable only when she is tired, and…
QUESTION TYPE: Flawed Reasoning
CONCLUSION: Roberta is probably irritable.
REASONING: Irritable ➞ Tired
Lose things ➞ Tired
Roberta lost her keys.
ANALYSIS: The argument has correctly shown that Roberta is tired. She lost her keys, so we definitely know she’s tired.
Being tired is a necessary condition for being irritable. But it’s not a sufficient condition. Roberta might not be irritable, even though she’s tired.
The fact about yawning is irrelevant to Roberta being tired. Knowing that Roberta lost her keys is enough on it’s own.
___________
- The argument never said that yawning is correlated to tiredness. This is a nonsense answer.
- This refers to circular reasoning. That didn’t happen.
Example of flaw: Roberta must be tired, because she must be tired. - This is a different flaw.
Example of flaw: Roberta only loses her keys when tired. So all people must lose their keys only when tired. - This is almost right. The argument did take a necessary condition for a sufficient condition. But it was a necessary condition for irritability, not for losing keys. This answer refers to the wrong term.
This answer was designed to trap you if you were rushing and just looking for necessary/sufficient. - CORRECT. See the analysis above.
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MemberSabrina (LSAT Hacks) says
Hi Yoona,
You’re right, both losing things and being irritable have the same necessary conditions.The key to this one is that the conclusion of the argument is about Roberta “almost certainly” being irritable, not about her losing things. It’s not suggesting that she must be losing things because she is tired, but that she must be irritable because she has lost something, which only happens when she is tired.
Her being tired is necessary for her being irritable, but it might not be enough (maybe having a bad day at work is also a necessary condition). In this case the argument concludes that simply because we know she is tired, therefore she is almost certainly irritable — and that’s the flaw!
Hope that helps!
Yoona says
Hi Graeme, quick question –
Don’t losing things and being irritable have the same necessary condition (tired)? That’s why I was so confused between D and E because I read that both mistakes being tired to be a sufficient condition.
If you could elaborate on this issue (or maybe I’m missing something obvious here), that would be super helpful, thanks! and thanks for all the amazing resources you’ve put up, they’ve really been crucial in my studying.