Logical reasoning PrepTest 144 · Section 4 · Question 6

Incorrect. There's no OR necessary condition in the conditional premise, so we can rule this one out without even starting to diagram it.

Incorrect. This answer only establishes one fact about Lois outside of the conditional, so it's not parallel. (This argument features an illegal negation, a separate conditional logic flaw.)

Incorrect. A neither/nor statement is actually an AND statement, so this conditional's necessary condition doesn't line up with the stimulus. (If that's not sitting right, think about this example: I had neither steak nor chicken for dinner, as I am a vegetarian.)

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Flawed Parallel Reasoning

Stimulus Summary:
Participate in regional band → Practice very hard OR Be very talented
Lily: Participate in regional band AND Very talented
Therefore Ð Lily: not Practice very hard

Answer Anticipation:
This Flawed Parallel Reasoning question is steeped in conditional logic, so we can rely on diagramming out each answer to find the correct one. However, knowing how the conditional logic is invalid can be helpful—especially when there are elements like the OR statement in the necessary condition, and the AND statement in the nonconditional information about Lily.

Here, the argument establishes that Lily meets the sufficient condition of a conditional with an OR necessary condition—that means one of the two necessary conditions definitely applies to her. However, the argument then establishes that she's definitely talented—one of those conditions—using it to conclude that she isn't the other.

That's a flaw, though—OR on the LSAT is inclusive in that it leaves open the possibility of having both options (unless it specifically says, "but not both"). Since the argument discounts that possibility, it's flawed—and we need to find an answer that similarly has an OR condition, establishes one option, and concludes the other isn't present.

Answer Explanation:
A quick read shows us that this has the OR necessary condition in that conditional premise and the AND nonconditional statement about Julie. That, coupled with no other answer having those parts, would be enough to select it, but we can also do a quick diagram to be certain:
Stay informed → Read major newspaper daily OR Watch CNN every day
Julie: Informed AND Reads major newspaper daily
Therefore Ð Julie: not Watch CNN every day

Key Takeaway:
A few quick hits: OR is inclusive, leaving open the possibility of both options. Neither/nor is an AND statement. And if those elements are important to the flaw/stimulus, and only one answer has them, you can pick that answer without diagramming it out as it's the only answer that could be correct.

Incorrect. This answer doesn't establish that Wayne got a ride home from the library, as the stimulus establishes that Lily participates in the regional band. Since this argument doesn't provide information guaranteeing that the conditional applies in this case, it's not parallel to the stimulus.