Logical reasoning PrepTest 141 · Section 4 · Question 25

Incorrect. While the argument does mention yawning, it ends up being a throwaway since Roberta losing her keys is sufficient to establish that she's tired.

Incorrect. The argument uses Roberta losing her keys to reach its conclusion, not a premise about her being irritable to reach the same conclusion. This answer is the circular reasoning answer, which isn't present here.

Incorrect. The conclusion is about whether Roberta is currently irritable, which isn't a generalization. (The premises, however, are generalizations, as almost all conditionals are.)

Incorrect. So close! However, the argument doesn't reverse the logic of the second conditional. The argument uses that conditional properly, basing a premise about Roberta losing things to lead to an inference that she's tired. The issue is when it applies the first conditional to that inference.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Irritable → Tired
Loses things → Tired
Yawning AND Lost keys
Therefore: Almost certainly irritable

Answer Anticipation:
The argument is replete with conditional logic, so this is likely some type of conditional logic flaw. Looking at the premises, we can see that there is overlap between the nonconditional premises and the second conditional. While her yawning is irrelevant to that conditional, her losing her keys does trigger the sufficient condition. That guarantees that she is tired—a valid conclusion that could be reached. However, the actual conclusion doesn't state that she's tired—rather, it states that she's irritable. Concluding that she's irritable based on being tired is an illegal reversal of the first conditional, so the correct answer will likely state that the argument is mixing up a necessary condition for a sufficient one.

Answer Explanation:
This answer highlights the flaw in the argument. Roberta being tired is necessary for her being irritable. However, the argument establishes that Roberta is tired and from that concludes that she's irritable. That's treating being tired as a sufficient condition for irritability.

Key Takeaway:
Conditional logic in an Errors in Reasoning question is almost certainly going to lead to a conditional logic flaw. However, as we see here, you may have to dig in a bit deeper to distinguish between answer choices that talk about that family of flaws. Don't get lazy on the LSAT! Do the work so you can finish a question without back-tracking. That said, if you do end up in a situation where you get this question down to (D) and (E) but aren't sure which one is right, don't beat yourself up—head back to the stimulus to compare the answers to the argument and go from there.