This is an important question to demonstrate that vacuous truths are tested on the LSAT. A vacuous truth is a conditional that is true because the sufficient condition is never satisfied (i.e., A -> B is true when A is an empty set). You can, of course, reason your way through this question without thinking about vacuous truths or the empty set, but it is precisely testing that concept.

The argument is:

Domain: "my students"

HfB = "heard Mercado's lecture from the beginning"

TF = "thought it was fascinating".

P1: HfB -> TF

P2: Assert TF

C: Some HfB

Identifying this as a form of a necessary for sufficient error is relatively easy. Identifying that it is making a special type of that error is a little trickier. The Professor is saying, given TF, surely at least one of my students (not necessarily the same one) heard it from the beginning. To show this doesn't follow from the premises, HfB within the domain must be the empty set (none of the Professor's students heard Mercado's lecture from the beginning). This allows the premises to remain intact (because HfB -> TF doesn't require there to be anything that satisfies HfB). Answer choice D doesn't say it in precisely that manner, but they are logically equivalent, given the premises of the argument are true.

@Tumptytumtoes By a taxonomy question, I mean the correct answer choices match members of an existing set of categories of "supports causal inferences". By being a representative member of a category within the class "supports causal inferences", they are interpreted as an answer that "lends support to the climatologists' (causal) hypothesis". It's a "does this shape fit in one of the available shape holes" type question. That's the way people taught and understood causal inference a few decades ago, and is still the way some professionals think about it.

The way I approach studying and analyzing LSAT questions is to attempt to derive the principles LSAT question writers use to develop questions. Any given test question depends on a construct they want to test and a discriminant function they want to use to separate people who understand the construct from people who do not. Interesting questions challenge prior assumptions, provide new information, alter the boundaries of what I understand about those elements (the constructs and the discriminant functions). Unsatisfying questions challenge them in ways I can't satisfyingly resolve. This is an unsatisfying question. If I run into another one with a similar issue, I can build a better mental model of the constructs and discriminant functions they use. With this approach, post hoc defenses of wrong answers being wrong and right answers being right are very important to identify (and very tricky), because, to be precise in discriminanting among test takers, the correct answer MUST be the correct answer and each wrong answer MUST be the wrong answer, using a set of rules that do not conflict with any other question in the question bank.

@Tumptytumtoes I think it's a mistake in LSAT prep to require one answer choice in an EXCEPT question to use the same type of support as the other. I don't know if that's convincing to you, but it seems self evident to me based on the structure of the question.

My claim is that D's support is mechanism to address a concession. That support, as part of an argument, requires attachment. You keep saying it's not an analogy or argument by cases, but I'm not sure why. I'm not arguing that it is. Maybe the term "attachment" is giving you that impression? If that's not the right term, then mea culpa there, but I'm not arguing it is an analogy or argument by cases. I'm saying it attaches, the attachment is substantial, and that is why this question is not satisfying.

Attachment point (1) large bits of cosmic rock: this is the same type of object as cosmic dust. It's a natural inference, certainly available in inference questions, present elsewhere in other LSAT questions so part of the language of the LSAT, that natural phenomena have variance in size. Bits of rock and dust are reasonably inferred to go together. Large bits, would be the larger size of these bits.

Attachment point (2) periodically enter the Earth's atmosphere. This is the temporal pattern of the cosmic dust clouds in the hypothesis. It doesn't say it's the SAME period, but again, this is an inferential question by nature.

This is the entire subject of answer (D). That it is large BITS of COSMIC rock, and that it periodically enters the Earth's atmosphere, attaches it to the hypothesis. The one problem here is that they are described as large, but large is an intensional quality that depends on the set it is describing. In natural language and on the lsat, to call something large means that it is large relative to the other members of the set.

Now, what is it doing? What is this subject that has successfully attached to the hypothesis doing? Is it cooling? We don't know. It doesn't say. It is causing (and we stipulate that it is true because of the structure of this question type, as demonstrated by the stem) additional dust as a downstream cause, providing a mechanism for increasing the density of dust during this periodic event. That is unequivocally supportive of the hypothesis by addressing the concession in the stimulus. I think this is an important teaching point, because people often get confused about what kinds of alternate causes weaken a causal claim and which kinds don't. A mechanism is a cause mediating the effect of a primary cause. If one were to say a medication doesn't produce its effect, the receptor it binds to produces it, one would be speaking nonsense, some language other than causal reasoning. Mechanisms are downstream causes mediating the effect of a primary cause. They support, rather than weaken, a causal hypothesis.

The only question is whether the inference from periodic dust to periodic bits of rock is too much of an inference. I don't think it is. That is why I think this question is only resolved by treating it as a taxonomy question.

@Tumptytumtoes Yes, it's inferential, as I said, but it's allowed to be inferential. A is inferential. B is inferential. C is inferential. E is inferential. They are ALL inferential. You are, post hoc, limiting D's support structure to that of plausibility. It must show that dust can cool. I'm saying it's an error to require D to only be read as if it were a worse plausibility argument. It's doesn't need to be a plausibility argument. It is an 'infer the primary cause can produce an effect that resolves the concession'. But that is not a classic category of causal support.

Just, structurally, when attempting to justify that inferential "EXCEPT" answer choices align with the answer key, blocking a single type of support (here, blocking plausibility support) is not sufficient. The question is not asking if it lends support to the climatologists' hypothesis in this particular way. You're saying, "ahh, but you see, you've misread the support structure that does not exist." That's not satisfactory, because it doesn't need to give that particular class of support. It needs to not lend any class of support.

To be clear, I'm not saying the LSAT writers are wrong. I'm saying it's an unsatisfying question, and that that is resolved by understanding it as a taxonomy question. (D) doesn't fit neatly into a taxonomy bucket. Despite (C) weakening in one way and strengthening in another, it does fit neatly into a taxonomy bucket, as do A, B, and E. Thus the logic of the question is the taxonomy of causal support.

@Tumptytumtoes I see what you're saying, but I think you're applying a more rigorous filter to D than to any of the other answers simply to justify the result. A doesn't say anything about cooling. Neither does B. C does, specifically, but due to volcanoes which are not explicitly or implicitly connected to the dust cloud. E implies it through a one step valid inference that ice ages are cold. So the lack of a "because it gets cold" element to D isn't a satisfactory reason, as it is not part of two other answers that we know support the argument. The support D provides requires an inferential leap, but so do other answers. D's support is that cosmic rock is the same as cosmic dust in type, just different in size, would likely be present in the same cloud. So now we have inferential support for the idea that the cosmic debris (which would directly dim the Sun in our hypothesis, but probably not enough, per our concession), also comes along with a mediating causal variable of raising surface dust, thus providing a mechanism to address the concession. I can only reconcile this as being classified as no support if we see the test writer here looking for things that fit standard classes of support. It's a taxonomy question. The one that is hardest to put in a classic causal support bucket is D.

Generally, I think it's important to be skeptical of post hoc justifications in order to convince ourselves of why an answer was wrong. They can dull our sense for the structure.

I used to be a classical musician and I think of high stakes tests like the LSAT as performances. The best advice I ever got from a teacher was that it's the sleep 2 nights before that really matters. Do the best you can to get good sleep the night before, but, you might have jitters the night before and it might not get as much sleep as you want. That's ok! Just be sure you ALSO do the best you can to get good sleep 2 nights before! You've got this!

Good example of the rare conditional conclusion. We know the antecedent is part of the conditional because of the structure of the earlier premises and the linguistic markers: "THIS SUGGESTS" is unequivocal that the thing that follows is the conclusion, so "IF A then B" is the conclusion, and anything weakening A doesn't weaken the argument.

I think this is a very unsatisfactory example of just having to learn what test writers expect. This question is looking for answer choices that match specific types of support. (A) is alignment in time (the phenomenon starts 800 000 years ago, so we establish that the cause starts with the phenomenon. (B) is an upstream cause, a specific mechanism for the appearance in time. (C) is plausibility (questionable in my opinion, but it aligns with a category of support). (E) is hard data supportive evidence of co-localization in geologic time, not just with the start of the phenomena, but the pattern. As an aside, E is probably the best support if that were the stem. (D), honestly, mechanistically, seems to me to be just as good as some of the others, it supports the existence of cosmic material periodically entering Earth's atmosphere, and to me, reads as helping satisfy the concession by being the upstream cause of a modifier that increases the density of dust clouds, but doesn't happen to fit a specific class of old school 'causality support'. My hope is that this kind of 'fit an old school type of causality bucket' question is going out of favor. It seems like, generally, newer PTs have more good quality modern causal inference informed questions than older PTs

@MaxThompson that's very much not a satisfactory answer in an "each lend support EXCEPT" format. It doesn't have to be a sufficient condition. It just has to lend support. If it lends support to part of the hypothesis, it lends support to the hypothesis. (B) doesn't support cooling either, and neither does (A).

@Peter_Bound if we're going to say that answer C supports the climatologists hypothesis by way of plausibility, we have to execute a similar logical maneuver to upgrade a slight drop in average temperature to an ice age. That feels like having it both ways. volcano -c-> large amounts of dust -c-> slight coooling -c-> ice age? if that's questionable as an alternative hypo then it feels like quite a stretch to say it lends support to the cosmic dust via plausibility.

@PhoebeHopp I don't know, I think it's just as reasonable to think that a cosmic dust cloud includes larger particles of the same material as it is to think that an alternate cause for cooling supports the hypothesis. Particularly when the bits of cosmic rock add additional material to the atmosphere to protect against the concession (that the clouds would have to be particularly dense).

Trust the stem. The stem is the one thing that will never lie to you. Sometimes things in the stimulus are not true. Sometimes things in the answer choices are not true. BUT NEVER THE STEM. The stem says "which of the following, if true, most calls into question the scientists argument" If the answer choice is true, the premise is false, and despite the rule it's breaking, it destroys the argument.

An interesting note, several of the wrong answer choices tried to play on the descriptive clause "similar to adult thrill-seeking behavior" the possibility of an analogy, and the possible term shift from the premise to the conclusion (impulsive behavior to thrill-seeking behavior). Grammar analysis helps here "engage in impulsive behavior similar to adult thrill-seeking behavior" is the predicate, "in impulsive behavior similar to adult thrill-seeking behavior" is the prepositional object. Adults don't have anything to do with the claim. Causal reasoning, by the way, doesn't require an effect to be stable. So even if, for example, A or D were more specific and clearly showed that any effect of the gene variant on impulsive behavior was no longer present as adults, it wouldn't matter. It still has a causal relationship.

This is a great example question for a MOST strongly supported question. Don't let yourself be convinced by this question that the (E) is strongly supported via causal reasoning. It is not. But it is more supported than any of the other answer choices. If your instinct is to reject (E), that's a good instinct. Does a bath cause other effects that might counter the body temperature mechanism? Maybe, we don't know. Does the timing of the body temp effect follow the timing of the exercise effect? We don't know. Both of these are large assumptions, but we're not trying to evaluate the likelihood that it does in fact do what it says. We're evaluating the support, which is a rhetorical question, not properly a causal inference question.

Recognize that we HAVE to accept that the mechanism is correct, as we have a premise that a slight elevation in body temp until slightly after bedtime causes deeper sleep. Given that premise, there is support for some other method to produce that mechanism, and answer choice (E) is very specific about what we get. It's not, "taking a warm bath will increase deep sleep". It's "RAISING BODY TEMPERATURE SLIGHTLY... JUST BEFORE BEDTIME will LIKELY result in increased deep-sleep." That's a restatement of the mechanism. We don't have to guess whether the bath does or doesn't produce that effect, the answer choice specifies that we're talking about a warm bath that does what the exercise did. Much of what makes this leap too large is dealt with rhetorically.

In the real world, a claim like (E) would be a good hypothesis for researchers to test. It would probably not produce the same effect as afternoon exercise, but it might, and it is absolutely rhetorically supported by the stimulus, which makes a very clear claim about the particular mechanism. Honestly, it reads to me like a simplified version of a report on a (surprising) finding that may have been reported in a physiology of sleep journal

@mcmcgurk I agree. If we take the premises to be true, (D) to be true, and only throw out the stimulus conclusion, then we have, within the domain Prof O'Brien's students: HfB -> TF, and we know in that domain there are no members who HfB and TF, meaning, any possible members in that domain who did HfB did not TF. This combination cannot exist along with the conditional HfB -> TF, so we know that they all either ~HfB and TF, or ~HfB and ~TF.

This is a great example of the difference between parallel principle and parallel reasoning. There is a modal shift between the stimulus and the correct answer, but they both apply the same principle: direct experience is better than general expertise.

@beenbrokebro this isn't a satisfactory explanation, as in the hotel security system and the screen saver, there is going to be a decision about whether to get the thing or not. Trade-off vs cost benefit is generally short hand that Ping is invoking for the things that make answer choice D and the stimulus count as the same, and make A, C, and E count as different, but it isn't particularly coherent. Traditionally, these are ALL cost benefit. To identify the correct answer, you need to go deeper structurally, and not by artificially restricting what cost benefit means.

@saulgoodman13 It absolutely is a cost benefit analysis in a traditional sense. JY Ping is suggesting that cost benefit is only when financial cost is compared to cost that is probably financial, and not when it's time compared to time (same axis, easily converted to money if you want to stick to what economists think cost benefit analyses are), and also not when comparing preference with money, or money spent on up front cost to money spent on repair cost. I think he's trying to say the principle of cost benefit is the thing we're looking for, and then artificially restricting it so that it maps to the correct answer, but if you want to invoke a principle to justify this question, I think you need to get more specific than "cost benefit", and articulate the things that make the stimulus and answer choice D different from the other cost benefit evaluations in the answer choices.

This is a very interesting question. It shows us a principle that isn't used to justify a prescriptive conclusion, but rather a descriptive claim. We also see weighting of different types of value comparisons in each of the answer choices. There is no clear out of left field answer choice here, and the one that is correct tells us a little something about this question type on the LSAT.

I am not sure where JY Ping is getting his terminology of "trade-off" vs "cost-benefit". There is a tradition in this sort of evaluation to consider comparisons along the same axis (financial cost vs financial benefit, or time cost vs time benefit) as different from comparisons along different axes (preference vs financial cost), but both are evaluating costs and benefits. Some traditions, such as economics, prefer evaluations that convert everything to the same axis (e.g., economists will convert time, lives, disability, and hedonic pleasure to money using market calculations), but Ping suggests there is a specific principle of cost benefit when the word cost is used and trade off when the word time is used. That's a pretty nontraditional way to think about cost benefit analyses, and I'd need to see some good evidence to believe the LSAT relies on that. The question here is not "which principle is right?" It's how many points of attachment or similarity are there between the stimulus and the correct answer choice. The actual principle is invisible. You don't need to write it down (it's clearly not just "cost benefit" as that applies to most of these answer choices), you don't even need to use one, unless it helps make it faster and simpler.

The most essential similarity to me between the stimulus and the answer choice, which I could invoke as a principle, I suppose, is the concept of a Trap, or an unexpected cost as a downstream effect not directly related to the intervention being evaluated. Unexpected or unanticipated are subjective, not structural, so maybe it would be better to define it as orthogonal. In the stimulus, the basic cost benefit evaluation is the (implied) cost of the screensavers, vs the (explicit) benefit of reduced electricity bills and reduced spend on equipment. The trap, or orthogonal cost is human capital, but described (vaguely) as cost, which I think we can presume means financial cost. (D) is very similar, with a traditional cost benefit analysis weighing the (implied) cost of the security system to the (explicit) financial benefit in losses by theft, but outweighed by an orthogonal downstream cost, customer goodwill (vaguely described as a cost, but presumably also financial).

I think, behaviorally, on test day, it might be useful to start with a heuristic principle if one jumps out, but the real question is how many points of attachment exist, and whether they are structural or simply language matching.

@LowriThomas The modeling of not all parrots have an equally pleasant disposition is wrong here. The 7sage curriculum doesn't teach how to relate terms to eachother, but your translation is invalid. The first order symbolic logic translation is \exists x \exists y DiffPl(x, y), where we define DiffPl(x, y) as have different levels of pleasant disposition. You could simplify to MPl(x,y), x has a more pleasant disposition than y. But to say some are pleasant and some are unpleasant is not at all an accurate translation of the comparative, and that's not just a trivial nit picky point. Anyone who starts to think relative qualities can be described as absolute qualities is going to eventually run into difficulty on this test.

As to almost all, that specifically means: most and some are not, e.g., in 7Sage LAWGIC symbols, P -m-> like owner ^ P <-s-> ~ like owner, but that's probably nit picking :) it's not necessary for the question and isn't encoding a key flaw.

Really fantastic session. Lin makes great choices of argument part examples and uses them establish boundaries and exceptions to common heuristics. I really appreciate the effort and execution here.

This is a tricky one that appears to break some rules for main point questions, but I think provides a good example of the exceptions to those rules. 1. The natural conclusion of the argument, given its mode of argumentation, is the modus tollens conclusions that the artist is wrong. That conclusion is not stated. It may be relevant to this that the stem doesn't say main conclusion. It says main point. Generally we consider those to be the same, but perhaps this illustrates the difference.

The point where the argument stops is the correct answer, and the 'main point' of the argument. The premises require us to resolve a dilemma from the conditional premise (if claim correct, then any music that is great art would imitate nature) and the counter example of great music that doesn't imitate nature. So answer (B) is precisely where the answer stops, but it is not properly a conclusion. It is not supported, as conclusion, by the premises. It's merely an entailment of the premises, without specific rhetorical support. The rhetoric and mode of argumentation doesn't attempt to establish the nature of the disjunction (or by material implication, the entailed conditional). Generally, in other questions, for a conditional to be the actual conclusion, it needs to have that kind of support. But here, we have no explicit conclusion and we're asked for a main point specifically. This may illustrate the narrow slice of main point that is not necessarily conclusion.

It's not necessary for the question, but is clearly an issue in the argument that, if there was a premise that all great music is great art, we could say the clear entailed conclusion is the MT conclusion of "the artist's claim is wrong". But we don't have that premise, and it is not a valid real world inference. I think this is the trickiest part of this question. Any explanation of this that we cannot assume music is a subset of art is deeply unsatisfying and, I believe, the wrong approach to the LSAT. That's the plain meaning of the words art and music, and if we can't rely on the meaning of words on this test, what are we evening doing. If you are pulled in that direction, that the conclusion is really 'the artist's claim is wrong', because it is airtight that all music is art, step back and recognize the assumption you've made. Just like most of a superset doesn't necessary entail most of a subset, great, even if we define it as some objective best proportion, say top 10%, the top 10% of a superset is not necessarily going to include exactly the same top 10% of the subset. And superlatives like great are often much more varied. They are partitioning functions that often depend on the characteristics of the set itself, even something as simple as how big it is.

Whoever recommended doing the shallow dip with the logical strength of the conclusion in the answer choices several lessons back is brilliant. it's been much easier than trying the shallow dip with the premises, and it's cutting my times in half.

This is a garbage question (by which I mean it lacks construct validity). It is presented as if the stimulus were an example of the “evidence reversal” flaw, where evidence pointing to a conclusion is used to support the rejection of that conclusion. Answer choice (A) is certainly an example of that flaw. The stimulus is not.

Why is the stimulus not evidence reversal? The owner may very well have stolen the diamonds, but the presence of his fingerprints has no evidentiary value. It is simply the fact that he had access. This fact is not used in the argument at all. If the presence of his fingerprints could support a conclusion that he participated, the absence of his fingerprints would reduce the likelihood that he participated in the theft. But, in fact, the absence of his fingerprints strongly points to his involvement. So the stimulus is NOT “evidence reversal”, it belongs to the larger category, presenting an unwarranted causal claim despite reasonable alternative hypotheses.

Choice A is ‘evidence reversal’ (the subset) where the stimulus is NOT evidence reversal. Choice A does NOT present an unwarranted causal claim, where the stimulus DOES present an unwarranted causal claim (Choice A merely rejects the likely claim). So there are no satisfying answers. I think, structurally, choice D is at least as good as choice A. Unlike the stimulus, it doesn’t take a baseline absence of evidence and posit a cause of that phenomenon (something happened and we have the absence of evidence), but it does take a phenomenon (cavities on one side) and makes an unwarranted claim about the cause, despite plenty of equally or more plausible alternative hypotheses (brushes less on the left, doesn’t floss on the left, only had one or two cavities and they happened to be on the left by chance, had an enamel injury or prior infection in an area of her mouth that makes that area more likely to develop cavities, etc etc).

There have been imperfect practice questions tests before, but still with a ‘best answer’ that follows despite not being perfect. Here, however, it really seems as if the test writers have simply fallen for a common logical fallacy (that physical evidence with no probative value, as it does not increase the likelihood ratio, can somehow support a claim it cannot). It’s very disappointing.