Structure of the argument: 1. Historical context: Moroccan troops defeated a Portuguese army and killed King Sebastian. 2. Weird phenomenon: Portuguese contemporaries did not record the death of King Sebastian. 3. Author's take on the explanation for this (eliminating an alternative explanation): It's not simply cause by ignorance. [implicit: at least some Portuguese contemporaries knew about the death yet chose to not record it.] 4. Author's evidence: 2 captured Portuguese officers literally stayed in the same prison cell with two soldiers who identified the King's body. [Implicit: there's no way in hell these officers did not know the King died.] However, these two officers DID NOT even mention the King's death in their battle records. 5. Author's take on the explanation - conclusion: The omission of the King's death had a psychological cause - the Portuguese found his death extremely humiliating.

The author briefly described the historical context, rejected an alternative hypothesis (ignorance led to omission), provided evidence countering the alternative hypothesis (the 2 officers who were NOT ignorant), and concluded with her explanation for the omission.

A - Spot on. The alternative explanation was ignorance.

just sorting my thoughts out:

[ Sober: 5/100 positive, coke user: 99/100] address the likelihood of the corresponding groups testing positive. I.e. coke users are more likely to test positive. Sobers are less likely to test positive.

This piece of info addresses the attributes of the sobers and coke users, NOT THE POPULATION.

[Majority of the positive results from the random sample] attempts to address something about the general population, since a random sample is a representation of the population. Yet, the premise does not support any claim regarding the population as a whole. All that was compared was the likelihood of sober users testing positive v. Coke users testing positive.

In other words, if you are a coke user, you are more likely to test positive, but this does not mean that, if you tested positive, you are more likely to be a coke user.

If you are a coke user, you are more likely to test positive: 99 positive test/100 coke user

If you tested positive, you are more likely to be a coke user: 51 coke users / 100 positive tests. (The exact numbers do not matter, as long as it’s the “majority”)

These two statements are based on completely different stats, and this is where the explanation and correct AC are spot on: we can’t assume 51 Coke users / 100 positive tests is true based on the premise. Maybe people rarely use coke, so 99% of the positive tests are actually sobers who tested false positive! That would mean 99 sober / 100 positive tests, which means the majority of the positive tests from the random sample are SOBERS.

The only reason I got this question correct was getting ungodly good at negating quantifiers after obsessing with the new LSAT games. Thank you 7sage #blessed

Structural breakdown:

Addiction's current definition: dependence on and abuse of a psychoactive substance.

Author's stance/conclusion: This definition is incorrect.

Premise: 1. (sub-conclusion) dependence and abuse do not always go hand in hand: dependence and abuse need not be concurrently required for defining a case of addiction.

1. Counterexample (to the current definition of addiction) #1: Cancer patients and morphine: dependence and abuse.

2. Counterexample #2: drug abusers: dependence and abuse

3. Implicit message: dependence and abuse don't always occur together in cases of addiction.

The author tries to show a definition is incorrect by 1. claiming dependence and abuse need not be required at the same time 2. provide two counterexamples to prove this point.

Key to spotting the necessary assumption: for a counterexample to even be relevant to the argument, it MUST be a case under discussion. If cancer patients and people who abuse drugs aren't addicts, then they are completely irrelevant to the argument, and why would the author even mention them then?

This is why C is correct. Negating C would mean cancer patients who are dependent on morphine ARE NOT addicted to it. Ok... Now why do we even care about these patients? We are trying to figure out how to correctly define an addict, and these people aren't even addicts!

Keep in mind, it is the PRESENCE of a counterexample that is necessary for challenging the definition, not the FREQUENCY of the occurrence of the counterexamples. A makes this mistake, and that's why it's unnecessary. We don't need every single cancer patient to not abuse morphine, we just need one cancer patient, who is addicted, to depend on morphine, yet not abusing it. Just one instance of this is enough for us to challenge the definition.

This is the best thing ever! I wish I saw this sooner. They are so fun.

The premise:

1. chance of being elected --> /support new tax plan.

2. understands economics --> /support new tax plan

the conclusion:

chance of being elected --> understands economics

Therefore, the author's assumption:

chance of being elected --> /support new tax plan --> understands economics.

What went wrong?

the premise stated that

understand economics --> /support new tax plan

yet the author assumed

/support new tax plan --> understands economics

This means the author has confused a sufficient condition for a necessary condition, or that the author has overlooked the possibility that there are people who do not support the new tax plan, yet does not understand economics (in other words, understanding economics guarantees that you do not support the new tax plan, but just because you support the new tax plan doesn't necessarily mean you understand economics). This is exactly what D stated.

B is very tricky, but it isn't something the author has overlooked, because the author's conclusion stated that truly understanding economics is a necessary condition for having a chance of being elected. This means that B: people who truly understand economics can still have no chance of being elected, is actually perfectly consistent with the author's assumptions and conclusion.

@TriambakaShriram great question! C doesn’t actually break the initial conditional. Because the conditional used “unless” instead of “if.”

There is a logical difference between “we should not restrict unless it negatively impacts others” and “we should not restrict if it negatively impacts others” (I know this sounds weird, but bear with me).

The principle stated in the stimulus uses the former: we should not restrict unless it negatively impacts others. In conditional form, this can be written as [/negative impact —> should not restrict] or [should restrict —> negative impact]

This isn’t a prescription for what to do when the action negatively impacts others. It only tells us that, IF we should restrict a certain action, then that action MUST negatively impact others. Therefore, the fact that smoking does cause harm to others and should not be restricted is actually perfectly consistent with the principle because should not be restricted is the necessary condition.

if you need any further clarification I’m happy to answer!

@Kb092100 this really is an “once you see it you can’t unsee it” type of question. The author implicitly made an assumption, then threw a bunch of premises at us. While we are preoccupied with dissecting his word vomit, AC E just quietly sat there like “dude it’s really not as complicated as you think.”

Simply put, what’s the point of arguing for building a house out of bricks when bricks don’t exist?

The hard part is eliminating D, but that’s also strangely simple: the premise only mentioned criteria for WHAT TO INCLUDE, not WHAT TO EXCLUDE, meaning even contradicting claims are welcomed by the definition. In other words, the definition’s composition doesn’t define the definition.

i feel like I need to sue someone for this.

@Stas1973 first of all, thank you for your reply(and reading my comment)! I 100% agree with you. Looking back, I think I was still making the mistake of not firmly anchoring myself to the argument. Your point about E being a failed attempt to directly attack the conclusion instead of the argument was spot on. The correct AC does the job of dismantling the author’s assumption that the prevalence of low-ceiling houses is an indicator of the causal relationship made in his conclusion, while the impact of “thermal-insulating technologies” wasn’t even stated. And like you said, even if it was stated, it still doesn’t necessarily weaken the author’s reasoning. Justifying E necessitates a bunch of unwarranted assumptions.

This was a mistake that I didn’t even know I was making back then. Fortunately I caught on eventually, your comment served as the perfect reminder that this is something I need to keep in mind :)

@EthanLucas of course, I’m so glad this helped! :)

On an abstract level, the author's argument stated that a condition (food producing capacity) that is conducive to counter a certain effect (no dooming war and famine) will change in the future due to a phenomenon (agriculture --> biodiversity loss).

It's the fact that this condition will change that supports the author's argument, the condition itself is still conducive to deterring potential food and famine. So, C is descriptively false. To justify C, you must make the assumption that food-production increase always leads to, or is equivalent to, agricultural advances.

Consider a parallel example: Running helps me lose weight. Yet chronic knee injuries will eventually make me bedbound, which prevents me from doing any physical activities. Therefore, my doctor's prediction that I will regain all my weight back is likely correct.

In this example, chronic knee injuries functions like agricultural advances, and running functions like increasing human food-production.

Chronic knee injuries will eventually cause me to regain all my weight. Why? Because it will prevent me from running.

It's tempting to assume running is actually a catalyst, because it's intuitive to assume running caused the injuries. BUT this is the LSAT, you can't just make your own assumptions. Maybe the knee injuries had nothing to do with my daily morning runs, and I actually broke both of my legs while skiing. And it's for this exact reason C is wrong, because I never suggested running is bad for my weight loss, it's the fact that I won't be able to run that is bad for my weight loss.

@Kb092100

To get a clearer view of why E is correct, not just because all other answer choices are wrong:

Another question that follows a similar logic is Section 131.S1.Q15.

In this question, the author attempted to refute a theory by appealing to another theory, but in this case, the author did not give any justification for why one theory is more valid than the other. So, the flaw is easier to see.

While in Q13, some justifications were given (people who regularly work with papercrete are more familiar with the material) for weighing one authority's validity over another (most builders who do not work regularly with papercrete).

E attacks the argument in a way that's almost like dragging Q13 down to 131 S1 Q15's level, by invalidating the justification for choosing one authority over another. If the consideration mentioned in E in which the author overlooked is true, then the author's argument is baseless, just like 131 S1 Q15.

I really appreciate this question; it points out a key feature of the LSAT: they want to see how good you are at clocking the exact argument without getting distracted.

The argument essentially appealed to an authority (those who regularly work with papercrete), the fact that they work primarily on small-scale projects is simply a characteristic of the group, not a key component of the argument. We can see this by replacing "small" with "medium", "huge", "enormous", "miniature" and the argument is unaffected logically.

In other words, what matters is that these workers "think otherwise", not that they "work primarily on small-scale projects."

E is correct because E attacks the authority part: the author assumed the group he appealed to has more expertise, but E said, "most builders have expertise as well, you can't assume your authority's opinion holds more weight than other builders."

One is likely to feel comfortable approaching a stranger if the stranger is of one's approximate age: approx age --> comfortable.

Most long-term friendships begin because someone felt comfortable approaching a stranger: long-term -m-> comfortable.

Conclusion: long-term -m-> approx age.

The author makes the assumption: long-term -m-> comfortable --> approx age.

This is wrong because the author's assumption [comfortable --> approx age] reversed the conditional relationship stated in the first premise [approx age --> comfortable]

The author overlooks the possibility that /approx age and comfortable, which is exactly what E points out. The author failed to address there's a chance that the sufficient condition (approximate age) is not the only trigger that guarantees the necessary condition (feel comfortable approaching a stranger).

Sidenote: a valid inference is long-term -m-> approx age --> comfortable. The argument would read something like [Since most long-term friendships began as two strangers of the same age approaching each other, long-term friends probably felt comfortable approaching each other when they were strangers]

I think of "probably" like a most claim because they are conceptually quite similar.

This question is my last straw.

@hsuyt25 I'm so glad it helped! :)

attempt at short cut:

Conditional:

/to prevent harm to others --> should not restrict

contrapositive: should restrict --> to prevent harm to others

The question stem asks for something inconsistent with the principle, therefore a must be false/contradiction. We know the contradiction of a principle/conditional is when the sufficient condition is true while the necessary condition fails. Therefore, any AC that mentions [should not restrict] or [to prevent harm to others](from the contrapositive) should be eliminated immediately, because all of them COULD BE TRUE.

eliminated:

A: disruptive to others = prevent harm to others

B: not talking about a restriction, irrelevant

C: public smoking should not be banned = should not be banned

D: often injure or kill other people = prevent harm to others

The correct AC must be E.

**As long as the necessary condition in the view aligns with the necessary condition in the original principle, it's essentially impossible to reach inconsistency.

E was attractive to me because it sounded close to a flaw that I spotted intuitively. The issue is that the author should've compared pledge v. non-pledged, not do not drink v. drink, since drinking is the outcome variable we are trying to observe. [feel free to correct me if this flaw is actually irrelevant?]

I was thinking the author confuses the claim that "the percentage of pledged adolescents who did not drink" with "the percentage of non-drinking adolescents who pledged". But this is not what E is saying.

If anyone else also struggled with E due to this, please comment!!!

@FarisPohan This requires a little bit of outside knowledge, carcinogenic means "having the potential to cause cancer." Therefore, saying something is carcinogenic is implicitly stating something increases one's chance of getting cancer. In this instance, the stimulus is claiming that galactose [under the condition of exceeding the body's ability to process it] is the causal factor in increasing one's chance of getting cancer.

Honestly I still think E is a solid alternative hypothesis, but C is just stronger, and our goal is to find the strongest weaken AC.

E's issue is that the thermal-insulting technology applied and the increased availability of A/C are not mutually inclusive causes. It's reasonable for them to concurrently impact the changes in the architectural changes.

C goes straight for the causal relationship. In the stimulus. the "cause" is A/C, and the "effect" is the thinner walls and lower ceilings. One way to attack a causal claim is to establish the effect occurs without the cause, and this is what C does essentially: thin walls and low ceilings are prevalent WITHOUT the demand for residential A/C.

Hierarchy of weakening strength?

Strong language for the correct AC of a necessary assumption question because the author is making a strong claim: ANY METHANE in the martian atmosphere -- this is an all-inclusive claim, no methane on mars is excluded. Therefore, all assumptions that the authors are making must also be all-inclusive. Hence B says, "all methane in the martian atmosphere."

B would still be correct if it states, "at least some methane in the Martian atmosphere is eventually exposed to sunlight".

Key: stimulus said ADAPTED genetically. A rule out the alternative hypothesis that interbreeding, instead of adapting, led to this genetical difference.

Translating E from an UNLESS statement to an ONLY IF statement for the sake of practicing conditionals:

1. Basics: a. negation of many will not (a <-s-> /b) is all will (a --> b)

2. breaking down the elements: [Many farmers in the region will not grow green-manure crops] UNLESS [they abandon the use of chemical fertilizers]

3. Since unless is a G3 indicator, I decided to take the negation of [many farmers will not grow] and place it in the sufficient condition slot

4. many farmers will not grow Negated: all farmers will grow green-manure crops

5. REPLACE UNLESS with ONLY IF, now [abandon the use of chemical fertilizers] is the necessary condition because it wasn't altered.

6. E is saying: all farmers in the region will grow green-manure crops ONLY IF they abandon the use of chemical fertilizers. This is exactly the big assumption gap in the stimulus. In other terms, the author is assuming that if the farmers do not abandon the use of chemical fertilizers, then they will not grow green-manure crops.

Taking the negation of E to see why it would break the argument:

1. Basics: the negation of a conditional relationship a-->b is a-->/b or a <-s-> /b

2. negate [abandon the use of chemical fertilizers]: don't abandon the use of chemical fertilizers.

3. version 1: a--> /b: [all farmers in the region will grow green-manure crops] only if [they do not abandon the use of chemical fertilizers]. This is technically a negation of E, but it sounds very extreme.

4. version 2：a <-s-> /b: [all farmers in the region will grow green-manure crops] even if [some of them do not abandon the use of chemical fertilizers]. or some farmers who do not abandon the use of chemical fertilizers still grow green-manure crops.

5. This breaks the author's assumption. Obviously since E is literally the assumption gap made by the author, of course a negation of E would also contradict the author's argument. But after translating it, it's more intuitive see how the negation of E actually does it. If the author is claiming that to make the farmers grow green-manure crops again, we MUST abandon chemical fertilizers, then this must mean the two methods are mutually exclusive. The negation of E, as stated in #4, points out there are some farmers who can do both at the same time, so the two methods are NOT mutually exclusive. Therefore, if E is negated and is true, then the author's argument falls apart.

I had a lot of trouble with this question, but honestly it just comes down to the fact that I didn't understand the core of the argument.

Question stem: evaluate the REASONING in the businessperson's ARGUMENT. Therefore, any argument that disregard the reasoning given by the businessperson must be wrong. We are NOT trying to evaluate the businessman. He was not trying to excuse himself from being late, he was trying establish the fact that the ONLY REASON he was late was because the parking lot maintenance.

The reasoning in the argument (I actually don't think this question requires the use of formal logic, but I think it's easier to see the structure this way):

1. because the parking area directly in front of the building was close, he was late. parking close-->difficulty parking --> late

1. maintenance done on a different date, I would've gotten to the meeting on time. /parking close -->(implicit: /difficulty parking)--> /late or late --> difficulity parking --> parking close

2. the businessman is essentially stating a chain of bi-conditionals: parking close <--> difficulty parking <--> late [domain: today, businessperson]. He is basically saying the only reason he is late today is the parking lot closure, and the only reason for there to be difficulty finding parking around the building is a parking area closure.

3. caveat: keep in mind that the domain is TODAY, or that the reasoning works for the businessperson TODAY. This alone eliminates D because he might be late every single day of the year, but that has nothing to do with his argument. If anything, D might be a form of ad hominem.

A. obviously incorrect, might as well turn the parking lot into a water park for all I care

B. Very tricky, but: 1. difficulty finding parking, but due to what? due to the parking lot maintenance? the answer choice never clarified. Maybe Sarah also had issues finding parking spaces, but she always parks her car 1 miles away at the closest mall to get her hot girl walks in. Then whether she had trouble parking at the mall has nothing to do with the argument. Maybe no one had issue parking, well, maybe the parking area was just one parking slot reserved for the businessperson, so of course he was the only person that was affected by the closure.

1. Even if the reason other attendees being late was due to the parking lot closure: Does NOT matter. Maybe everyone had a backup parking slot planned well before the maintenance, maybe everyone knew about the closure ahead of time and biked to work that day. Using B against the businessperson would be like saying "if other people could get here on time, why couldn't you?" This is the counterargument your mean supervisor uses when you try to explain yourself, and you cry about it in the shower after work.

C. is subtle, but it points out an important gap in the businessperson's argument: maybe the difficulty of finding parking had nothing to do with the maintenance. If the parking spaces around the building are always filled, then maintenance has nothing to do with the fact that the businessperson had trouble finding parking.

Looking back at #3's bi-conditional chain, C breaks his reasoning at difficulty parking <--> parking close.

The way to break a bi-conditional A <--> B is to show A and /B, if C provides that the parking area around the building are always filled, then it provides difficulty parking and /parking close (parking open), this contradicts the reasoning in the businessperson's argument.

Of course, If the parking spaces are always empty, then A and B hold true, this provides some support for his reasoning.

D. Discussed in #4, ad hominem, does not affect the reasoning of the argument.

E. I hope it was particularly important and his supervisor fires him