Logical reasoning PrepTest 113 · Section 3 · Question 21

Flawed

Flawed Parallel Reasoning Questions / Sufficient & Necessary Questions

Deposit credited on date of transaction → Made before 3pm

Alicia knows the deposit was made before 3pm

Don’t skim over the question stem here too quickly - it tells us that we need to match up two errors in reasoning here!

One of them is much easier to spot than the other. The stimulus starts with a conditional rule (“only when”), and then it establishes that Alicia knows the necessary condition of it was met, and concludes she knows that the sufficient condition will be met, as well. That’s an illegal reversal, so we need an answer that does the same thing.

The second flaw is harder to spot, but there is a concept raised that is related to a common flaw - what Alicia knows. Whenever the LSAT talks about someone’s subjective belief or knowledge, there’s always a chance that it’s messing it up. Let’s assume for a second the conditional logic wasn’t reversed. Does Alicia knowing that the deposit was made before 3pm guarantee that she knows it’ll be credited on the date of the transaction? It does not - she’d also have to know the (reversed) conditional. It’s possible that Alicia doesn’t know the timeline on which the bank credits deposits. We do because it’s established as a premise, but we can’t assume that just because it’s a fact that Alicia knows it.

Now, would you have definitely spotted this second flaw while working through this question? Nope. You may have missed it (though in the future always consider a Perception vs. Reality flaw when the argument discusses beliefs or knowledge). If that’s the case, you can still head into the answer and eliminate those that lack the illegal reversal, and then rely on finding an answer that mirrors the other aspects of the stimulus to pick an answer that’s more likely to be correct.