I fell for (A) during my actual take. Now I realize why (A) does not descriptively weaken the argument: (A) deals with an irrelevant and unhelpful group of students -- O'Brien's students who had no listening exposure to the lecture. The fact that these students find Mercado's work interesting tells us nothing about what they thought of the lecture -- and in fact, we can reasonably infer that these students didn't fall into the "fascinating/not fascinating" camps, since these students didn't hear the lecture! Someone who didn't hear the lecture can't reasonably be sorted into those categories.

(A) would be a good answer choice if it said "some of Professor O'Brien's students found Mercado's lecture fascinating but were unable to attend the lecture from the beginning." But that's not what (A) says.

I think (A) is a pretty smart trap answer, to LSAC's credit. It begs us to focus on the question of whether "very interested" and "fascinating" can be understood as reasonably equivalent...all while missing the problem with (A) -- that it deals with a group of students unhelpful for evaluating this argument.

(E) is a perfect way to express the "lack of support vs. false evidence" flaw. I incorrectly chose (A) by 1) mistakenly disputing the premise, and 2) failing to recognize that even if (A) were descriptively accurate, doing what (A) suggests is not a flaw (as discussed in the written explanation for (A)).

On my actual take, I should have felt skeptical of the wording of (A) without getting too into the weeds on it. Then I should have seen how great of an AC (E) is, picked (E), then moved on without feeling like I had to have a perfect sense of all the logical nuance of (A) to eliminate it.

@ryanlattavo516 I think one thing that you overlooked in your explanation is that "either/or" actually does let us infer the presence of one condition based on the absence of the other condition (not to be confused with "or" alone, which doesn't let us make this inference). I agree, though, that the descriptive/normative gap is another flaw in this argument.

As to why (E) is acceptable even though it seems to be fighting a premise, I think user "srusty" gives a helpful response on the PowerScore blog (Jan 14, 2024 comment).

Building on that explanation, the stimulus sets out a conditional relationship: either "can fight for anarchy" or "can tolerate totalitarian government control." The "either/or" construction allows us to infer that "can fight for anarchy" --> "can't tolerate totalitarian government control." And conversely, "can tolerate totalitarian government control" --> "can't fight for anarchy."

The second sentence of the stimulus seeks to show a drawback of tolerating totalitarian government, which, if we assume that shows that "can't tolerate totalitarian government control" obtains, means that people "can fight for anarchy." Note the can here. The fact that people can fight for anarchy is not sufficient to prove that people should fight for anarchy...to make this (albeit subtle) logical leap, as the stimulus does, we are assuming that anarchy and totalitarianism are "the only two political alternatives that are available," just as the stimulus says.

@aborges0428418 I think I see what you're saying, but to be fair, AC (D) says "for workers," not "for all workers." So even if this pattern only holds true for the workers with little training (the ones mentioned in the stimulus), (D) would still be fair. It would be a big leap, however, if (D) said "for all workers."

@fl7dqf252 Interesting point. It's true that, for all we know, it's possible for mussels to be farm-raised (and thus not contain sand) even though they aren't available at a seafood market (e.g. say they're shipped to your home directly instead).

The reason (E) is still necessary, even in light of the above, is that for the argument's premises to support the conclusion, i.e. for the argument itself to remain tenable, (E) must be true. So even though there is a way to reach your intermediate conclusion -- that the mussels you are using don't contain sand -- without having the mussels come from a seafood market, there is no way for your premise "...because the mussels available at seafood markets are farm raised" to support your conclusion without making the assumption in (E).

There's some interesting talk on this thread about people being amazed at how lots of people missed this. I don't think that's necessarily fair...One potential reason is that some high scorers may have had the same question you had and thus have had some hesitancy about (E). But even with that hesitancy, (E) is still necessary. Another reason could be what JY highlights about (B) baiting us into making an unwarranted assumption.

@Al_foroodian@sfu.ca This is an amazing explanation. I hopped over the comment section to see if anyone had gotten hung up on the same point as I was, which you stated very well under "Criticism #1 Explained." I think your answer at the end of your comment is spot-on. Thanks for sharing!

(A) strengthens this hypothesis through an interesting approach that I don't remember seeing before in an LSAT question: it gives evidence of a compensatory mechanism to support a hypothesized function of a trait.

Here's a real-world example of this way of strengthening a hypothesis in case it helps: suppose sunlight is hypothesized to facilitate the production of vitamin D in humans. Scientists have found that in the absence of sunlight, but not in the presence of sunlight, the liver secretes a chemical that facilitates the production of vitamin D. This fact supports (though of course doesn't prove) the hypothesis that sunlight facilitates the production of vitamin D.

Yes, you're right about the example you gave -- being an apple is sufficient (i.e. enough to guarantee) that something is a fruit. In other words, being a fruit is necessary (i.e. required) for something to be an apple. At a conceptual level, we can also think of this as "If something isn't a fruit, it isn't an apple." That's called reasoning by the contrapositive: since apple --> fruit, then /fruit --> /apple. I'd say it could be helpful to get comfortable contraposing logical relationships -- first in the real world (e.g. dog/animal, chair/furniture, water/liquid, etc.), then with more abstract symbols. After that, practice representing sufficient and necessary conditions symbolically using circles. Sticking with the apple/fruit example, "apple" would be a circle that is surrounded by the bigger circle of "fruit." These circles show you something important: it is possible to be within the necessary condition (i.e. be a fruit) without being inside the sufficient condition (i.e. being an apple) and likewise that being outside the outer circle ("fruit" circle) guarantees that you are also outside of the inner circle ("apple" circle). Visually, sufficient conditions are inner circles and necessary conditions are outer circles. I think knowing both the symbolic and the visual ways to represent sufficiency and necessity is really useful groundwork for understanding a lot of LSAT question types and logical flaws.

And as an additional challenge, you can start working with several conditions at once to see how "sufficiency" and "necessity" are relative terms that depend on the conditions you are referring to. For example, "person" is sufficient for "organism," which is sufficient for "living." Therefore, "living" is necessary for "organism," which is necessary for "person." So /living --> /organism --> /person.

@lsattaker264 This was my hang-up too!

(D) can be thought of as strengthening the argument by dispelling a potential competing hypothesis (that tourists were staying in the city longer for their visits and thus spending more on hotels and food, without increasing the amount of money spent on passes).

For (E) to actually weaken, we'd need to assume that the painting of the historic battle accurately represents the figures involved in the battle (and does not include any additional figures). That is a major and unwarranted assumption, especially considering that (D) marginally weakens without needing any such assumption.

@Xexne198 That's fair. I think the main issue with (B) is that the two possible outcomes -- "succeeds" and "fails" in the stimulus, which are opposites of one another -- aren't opposites in this answer choice. (D), on the other hand, maintains this "pair of opposite outcomes" relationship.

Using the method of reasoning in the stimulus, we could similarly argue that, because floods have always been preceded by rain, the fact that it's raining outside means it's about to flood. But that would be unreasonable! Consider that floods only follow a tiny portion of rain episodes.

The abstracted flaw is: X has always been preceded by Y. Therefore, the presence of Y means that X is impending.

(E) matches that abstracted flaw.

If it helps, you can also think about this as a quasi-sufficiency/necessity mistake: in our domain of discussion, earthquake --> tremors came before. Tremors came. Therefore, earthquake is coming.

@mh212529 The question stem says "to the policy...not advocated by the author of passage B?" The way this question is phrased does not require outright rejection by passage B. Rather, the correct answer choice simply needs to express a policy that was advocated by passage A and not advocated for by B. "Not advocated for by B" can mean an outright rejection of the policy, a hint at a rejection of the policy, or no mention of the policy -- anything so long as it is not advocacy.

@nicoleegatto791 I agree. I don't love how the written explanation for (C) says that "The analogy isn't between the info processed by a brain and the info transmitted by the Internet," since there is in fact an analogy between those two means of transmitting information as stated in the first sentence of the stimulus. Then there's a second analogy about the brain and the Internet. It's just that it's this second analogy that is the dubious one, not the first, hence why (C) is wrong.

@ZachSadorra I think I see what you're getting at here. Here's how I'm thinking about this. I think JY's diagram in the video is helpful, parsing out "things we (the readers) know" and "things this group believes."

For (A), "Many people who criticize etiquette have contradictory views of etiquette" is unsupported. All we know about this "many people" group is that: 1) they believe that etiquette has no beneficial effects for society and 2) they believe that kindness and social harmony are good. Do those two beliefs alone contradict one another? No. Perhaps this group simply doesn't believe that etiquette promotes social harmony, even though we know -- as a factual matter from the factual premise found in the first sentence of the stimulus -- that etiquette does in reality promote social harmony. But again, we don't know whether this group of people believes this fact. Without knowing whether or not they believe this fact we are given, we have no evidence of internally contradictory beliefs about etiquette.

Now for (C), "Many people who criticize etiquette are mistaken about its beneficial effects for society." The operative word here is "mistaken." Notice that (C) doesn't specify exactly how this group is mistaken. There are a few ways. Consider this one: this group of "many people" believes that etiquette has no benefit for society. We are told that, in reality, etiquette promotes social harmony. Why is that relevant? Well, this group believes that social harmony is good. So this group is mistaken in their assessment of etiquette: if this group of people adopted belief in the fact presented about etiquette -- that it promotes social harmony -- then they would be forced to abandon their belief that etiquette has no societal benefit, or vice versa, to prevent internal contradictions. But as it stands, this group has a belief about etiquette that is mistaken relative to what we are told about reality: based on their belief that social harmony is good, they are mistaken that etiquette produces no social goods. Why? Because we are told -- as a factual, not belief-based, matter -- that etiquette promotes social harmony.

So the sense of "mistaken" here is an incongruence between reality (etiquette promotes social harmony) and belief (etiquette produces no benefit for society, even though this group believes social harmony is a benefit for society).

(A) is dealing with internal incongruence ("contradictory"), whereas (C) is dealing with the incongruence between belief and reality.

I struggled with this question but hope my long-winded answer helps at least a little bit here.

To add on to why (C) is wrong: (C) might very well be useful in explaining this trend if we were told whether Jones's theory is a line of research that scientists in the field generally accept. That would possibly help explain why more scientists are doing research along the lines of Jones's work, and if the scholarly consensus is that Jones is correct, and she is in fact correct, then it is reasonable that these additional data points (corrections) are in line with Jones's thinking. But we aren't told whether Jones's theory is regarded as such.

Combine that with the issue the written explanation points out and I think you get a strong reason for rejecting (C).

@lilikim2002275 This was my concern too. I think it comes down to having to make the assumption that, by fulfilling a NC, you increase the likelihood of obtaining the SC in some cases. While not always true, it's a smaller assumption than conflating sufficiency and necessity.

The written explanation for (D) currently says, "The nerve sheath will not disintegrate if it contains living nerve tissue." That explanation is wrong because it confuses sufficiency and necessity in translating the "unless" relationship. I messaged 7Sage and they said the content team is going to update the explanation accordingly.

@rahenderson407 I see what you're saying. I think it comes down to the fact that (B) deals with slowing or stopping disintegration after the disintegration has already begun, whereas the stimulus tells us about when disintegration might begin. This difference in the domains being discussed in the stimulus and in (B) makes (B) unsupported.

(D), on the other hand, requires the assumption that the fulfillment of a NC increases the likelihood of obtaining the SC in some cases. While this isn't airtight -- we can think of situations in which fulfilling a NC does not increase the odds we obtain the SC -- it's a reasonably supported assumption in the context of probabilistic reasoning on a diverse data set.

Take that all with a grain of salt, but that's the conclusion I've come to with this question.

@AiXing I agree. I submitted a note on that through the "ask a tutor" button, so hopefully they'll fix the written explanation for (B).

@lsatscorer1239 As Mike Kim mentions in LSAT Trainer, there will only be one AC that weakens for weaken questions and only one AC that strengthens for strengthen questions, meaning you don't have to worry about assigning how many "utils of weakening" different ACs do and then choose the one that does the most weakening. As Kim points out, requiring this kind of comparison would lead to ambiguous questions, since it's very difficult to quantify to what degree different ACs weaken an argument...a recipe for disaster and bickering on a standardized exam like the LSAT. But it does not require any arbitrary quantification to determine whether an AC does or does not weaken an argument.

That said, for some high-level weakening questions, particularly ones that might have multiple ACs that could conceivably weaken the argument if you provide a set of assumptions with the AC, you will need to choose the AC that results in making the fewest significant assumptions possible. But even then, the question I still ask myself is "Which one of these ACs weakens the argument/which 4 do not weaken the argument?"

@Intersection The thrust of the scientist's argument is that the two premises (no active volcanoes identified and cyclical atmospheric composition) are sufficient for us not to accept the conclusion that volcanic activity caused the spike on Venus. By suggesting that Venus's conditions make it unlikely that an instrument would detect volcanoes directly, we are pointing to the possibility that there are in fact active volcanoes on Venus, just ones that haven't been detected directly.

Even with that being said, I'm sympathetic to your broader critique of this question. In reality, the scientist is simply saying that we shouldn't accept the grandiose conclusion that volcanic activity caused this spike on Venus. I'm inclined to think the scientist could still accommodate (A) to his argument, saying that "Sure, I grant that we don't have instruments that are likely to detect a volcanic eruption directly, leaving open the possibility that there are active volcanoes that we simply haven't detected. But my point is more modest: there is sufficient reason for us to doubt the conclusion that active volcanoes caused this spike, and the mere possibility of the existence of an undetected active volcano is not sufficient reason to believe that there is in fact an active volcano and that that active volcano was the cause of the spike." At least if I were the scientist, that's how I'd response to (A), the alleged weakener.

I think this question begs the question of what we actually mean when we say that an AC "weakens" an argument. If I'm the scientist and someone expresses (A) to me, I can still articulate how my conclusion can be legitimate even if (A) is true...But the truth of (A) nonetheless makes my first premise (that no active volcanoes have been identified on Venus) less powerful in triggering my conclusion than it otherwise would have been. I essentially then have to show that even with my weakened premise, my conclusion -- that there is not sufficient reason to conclude that volcanoes were the culprit -- has legs. So at the end of the day, I think it is for that reason -- that (A) makes the force with which that premise supports my conclusion less significant -- that makes (A) a legitimate weakener.

Sorry for the wordiness -- mostly wrote this as a way of externally processing this question. I think this stimulus is more complex than JY gives it credit for in the video.

Also, in a weird way, I think we can almost use an NA-esque approach to this question to see why (A) is a weakener. For the premise that "No active volcanoes have been identified on Venus" to support the conclusion that we shouldn't accept the claim in question, what needs to be true? Well, there needs to be some connection between what we detect and what's actually there, a sort of necessary assumption! By that logic, a way of weakening this line of reasoning is by suggesting that the necessary assumption does -- or might not -- obtain. What does (A) do? Suggests that the necessary assumption -- that there is some connection between detection and reality -- might not be true, by suggesting that the instruments we have can't detect things directly that might actually be there! I know that's kind of a weird mash-up way of thinking about this weakening question, and one I haven't really used on other weakening questions before, but I think it does explain why (A) actually does function as a marginal weakener.

This question is basically getting at why it's important to have a control group when assessing whether some experimental condition causes a change.

Here, there are other potential reasons for why fewer pears were lost to insects with the use of the new pesticide compared to the previous years. Perhaps winters were colder, meaning there were fewer insects alive during the warmer months to eat the pears. By having the control group described in (C), we can more meaningfully deduce whether the change we noticed with the use of the new pesticide was actually do to the pesticide or some other confounding variable.

@lazar.steven-1-1 Don't forget that, for PSA questions, over-broad principles/PSAs are fine...they get us to our conclusion and then some. You're right that (B) is wrong here, but I just wanted to mention that because it seemed like you were suggesting that over-broad PSAs/principles shouldn't be selected in PSA questions, which isn't the case.

@batcam28 I'm also confused as to the difference JY draws between the interrelation among sets and the membership of an object to a set. To me, that distinction seems a bit arbitrary, since we can just as easily conceptualize objects as subsets. Would appreciate help if anyone's figured out a good way to think about this! #help