Logical reasoning PrepTest 148 · Section 3 · Question 24

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:

(1) Widely acknowledged significance-most-Restored
(2) Restored-some-Authenticity suspect
(3) Restored → Safety ensured during process
(4) not Frequently consulted → not Restored

Answer Anticipation:
This stimulus provides a combination of quantified statements and conditional ones—everyone's favorite type! Here, the first step is to take the contrapositive of statement #4 so that each statement has an overlapping term (Restored, as opposed to not Restored):

(4) Restored → Frequently consulted

With that done, we have two options—we can go through and make inferences now, or we can go through the answers and try to "back solve" by identifying an answer that looks provable, and then seeing if we can combine statements to prove it. The latter will be much faster, but we'll go through all the combinations in the Takeaways section so you can get practice in.

Answer Explanation:
This answer relies on combining statement #2 and the contrapositive of #4. Taking a look at those, we can, in fact, combine them, since #4 talks about all of the restored work and #2 talks about some of it—there must be overlap. So it can be inferred that at least some of the suspect manuscripts are frequently consulted.

Key Takeaway:
The valid combinations for practice:
1+2) No valid inference (you can never get an inference from a most and some statement).
1+3) Widely acknowledged significance-most-Safety ensured during process (this is the one time when you can combine a quantified statement to get anything other than a some statement).
1+4) Widely acknowledged significance-most-Frequently consulted (note that 1+3 and 1+4 have the same construction and so lead to the same type of inference).
2+3) Authenticity suspect-some-Safety ensured during process
2+4) Authenticity suspect-some-Frequently consulted
3+4) Safety ensured during process-some-Frequently consulted

A few things to note! First, learning how to quickly make these inferences is a pain, but it's generally worth 1-2 points on the LSAT—so sit down and memorize the combinations. Second, note the combination of statements #3 and #4—two conditionals that share a sufficient condition can be combined to form a some inference. Finally, note the correct answer—it picked the least intuitive inference that could be made (why are researchers frequently consulting suspect manuscripts?). Don't use "common sense" in conditional/quantifier questions—use logic.

Incorrect. We only learn about most of these works in the stimulus, so this answer is too strong right off the bat.

Incorrect. We only learn about some of the works whose safety can be ensured, so this answer is too strong right off the bat. In any conditional or quantified statement, the quantifier (or "all" in the case of conditionals) only applies to the "left side" of the arrow—the other side is only guaranteed to be talking about some of that term. (Think about it this way: Humans → Live on Earth. This is talking about all humans, but only some of the things that live on Earth.) This answer would require a conditional chain between statements #3 and #4, but we can only combine them using our quantifier rules, not our conditional ones.

Incorrect. Nothing in the stimulus talks about different susceptibility to deterioration, so this answer is out of scope.

Incorrect. not Frequently consulted → not Widely acknowledged significance. Diagramming this out, we can see that one term—not Widely acknowledged significance—isn't discussed in the stimulus, and we can't infer it from statement #1 (since you can't contrapose a most statement), so this answer is out of scope.