Logical reasoning PrepTest 130 · Section 3 · Question 18

Incorrect. This answer would allow the conclusion to be drawn that both of two pesticides shouldn't be legal, but the stimulus is fine with all three of the named pesticides being legal. As such, the conclusion doesn't line up. Note that for this answer (and others) we can't rule it out because it talks about "[t]wo" or "both" pesticides, as the principle would apply to each combination of two pesticides in the stimulus and thus a conclusion about all three pesticides could be reached off of such a principle.

Incorrect. These pesticides are all harmful to the environment, just at varying levels, so this answer would justify a conclusion that they shouldn't both be legal. The stimulus, however, leaves open the possibility that they all should be legal, so this answer also doesn't line up with the conclusion.

Incorrect. Taking the contrapositive of this answer to get it to line up with the way the argument works, we get: not Both are harmful to the environment → not Both illegal. However, all of the chemicals are harmful to the environment, so this answer doesn't line up with the stimulus.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen (Principle)

Stimulus Summary:
Old belief - T is really harmful (so it was banned); E and Z aren't (so they weren't banned).

New studies - E and Z are more harmful than T.
Conclusion - Either E and Z should be banned, or T should be made legal.

Answer Anticipation:
Strengthen (Principle) questions generally task us with justifying a judgment in the conclusion based on details in the premises. Here, however, the judgment isn't straightforward—it talks about what "should" be done, but it leaves open two mutually exclusive options. Either E and Z should be banned, or T should be made legal.

How does this change the current states of affairs? Well, currently, T is banned and E and Z are legal. So the author wants to switch from treating these chemicals differently to treating them the same.

Why? Because the ban on T happened when it was believed T was environmentally damaging, but E and Z weren't. Now we know that E and Z are more environmentally damaging than T. So because these two chemicals are worse than T, they should either be banned as T is, or T should be made legal like they are.

Note that the author doesn't really care about the environmental damage—she seems fine with making all three environmentally damaging chemicals legal. What she cares about is the different treatment and, as it stands, the harsher treatment of the less damaging chemical. Since that's what she's focused on, it's what we should focus our anticipation on:
If one chemical is less damaging than another, then it shouldn't be banned when that other chemical isn't.

Yes, that's a little convoluted, so we're going to have to be careful as we work through the answer choices, as we can definitely see the LSAT phrasing this concept in a very hard-to-follow manner.

Answer Explanation:
Finally, an answer that talks about treating the pesticides differently! This answer is a bit tricky because it doesn't talk about the pesticides generically—the answer connects the sufficient and necessary condition by talking about the "former" and "latter" pesticides. So we'll have to do some translating here. Doing, so, we get:
One pesticide should be legal and another illegal only if the legal on is less harmful than the illegal one.
Contrapositive? If a legal pesticide is not less harmful than an illegal one, then it shouldn't be the case that the legal pesticide is legal and the illegal one illegal. Or, in other words, we should make the more harmful and legal pesticide illegal, or the less harmful and illegal pesticide legal. That matches the stimulus perfectly, so this is the correct answer.

Key Takeaway:
This is an exceptionally difficult Strengthen (Principle) question, so don't feel bad if you struggled with it! What you can focus on in a similar question in the future is specifically what the conclusion states. Here, the argument is very clear that, at the end of the recommended changes, the pesticides should be treated the same.

Incorrect. As soon as you see "harmless" here, you can rule this answer out—the pesticides are all known to be harmful.