LSAT Q&A: Ask the Experts Forum

[LSAT Blog]

lemme add this to the mix: Lawyers, Athletes, and Bankers (I think it's from PT 59).

It's PT59, Section 2, Q19

When you see a stimulus like this one, with lots of Formal Logic-type language (conditional statements), you can treat it like a Logic Game and start diagramming.

B, A, and L are all at the meeting.

B -> A and NOT L

Contrapositive:

L or NOT A -> NOT B


We can't predict exactly what the correct answer will ask for, but we can run through the choices looking for things we know based upon these conditional statements.

Correct answer is (C): We know that not all athletes are lawyers because bankers are present, and we know that bankers are athletes but aren't lawyers. As such, we know that at least some athletes aren't lawyers - the bankers.

Does that clear it up?

[outlookingin]

lemme add this to the mix: Lawyers, Athletes, and Bankers (I think it's from PT 59).

It's PT59, Section 2, Q19

When you see a stimulus like this one, with lots of Formal Logic-type language (conditional statements), you can treat it like a Logic Game and start diagramming.

B, A, and L are all at the meeting.

B -> A and NOT L

Contrapositive:

L or NOT A -> NOT B


We can't predict exactly what the correct answer will ask for, but we can run through the choices looking for things we know based upon these conditional statements.

Correct answer is (C): We know that not all athletes are lawyers because bankers are present, and we know that bankers are athletes but aren't lawyers. As such, we know that at least some athletes aren't lawyers - the bankers.

Does that clear it up?

Excellent thank you!

[MLBrandow]

57.3.20 (parallel flaw, formal logic)

I spent too long on this question, maybe three or four minutes. I generalized the stimulus as "All, All, Some are not, therefore Some are not." I went to the answer choices and to my dismay, only one actually violates this structure (D) although I didn't notice it at the time.

I then proceeded to diagram the stimulus, followed by (A) wrong, (B) wrong, (C) wrong, (D) wrong, and finally (E) hooray!

Is this question designed to be mean? A parallel flaw question with formal logic that has at least four answers with identical structures and no superficially discerning qualities between them?

Is there perhaps another method I can employ to not stall out here?


Also, 57.2.19 (parallel, formal logic)

I spent maybe three or four minutes on this question as well, but only because I didn't realize that the answer (A --> B ---> C ; A --> C) could be matched by (A --> B ---> C ; ~C --> ~A).

I've never seen this before on another parallel question, if only because it's the sole remaining "packet" of questions by type I've not yet approached. Had I realized this was fine intuitively, I'd have probably cracked this problem in a minute or less.

Are there other questions like this one that anyone has seen, or is this a bit unique in its usage of the contrapositive in this manner?

Thanks for any help!

[Dave Hall]

I was discussing PT47 with another TLSer, and we both had difficult with question 5 on the RC section. I'd like to hear what the experts think about that question and the answer choices. It's from the passage about ministers involved in the Downstate campaign.

The nice thing about RC questions is that we're always able to find the answer there in the passage: Every question is asking us what the passage says.

(A) In the middle of the second paragraph, we're told that they'd been working for years to achieve full civil rights. This action, then, did not represent a significant departure from their overall goals. Though it may have indicated a shift in strategy - tending for this project away from mediation and toward activism - this shift doesn't indicate a change in their general goals; just in the means of achieving them.

(B) Certainly other ministers did (the last line of the passage), and it's reasonable to assume that these guys may have, too, but the passage doesn't say that they did. So this cannot be our answer.

(C) Take out "in the construction industry" and we'd have a winner. Nothing here, though, about prior work in that industry.

(D) That "some... activists" considered the agreement incomplete doesn't tell us (A) which activists/groups in particular thought that way, nor (B) whether those activists/groups criticized the ministers for it. Passage doesn't say it, so it's out.

(E) It's possible that some hadn't, but the whole second paragraph exists to tell us that many of them had been so involved, and to describe some of the ways in which they had (mediation, running for office, etc.).

And the cool part is that it's always this way - the answer is the thing that the passage says is true.

[Dave Hall]

Dave,

I just wanted to say thanks for this advice on parallel flaw formal logic questions. I redid what I would have considered one of the more difficult LR problems in 61.2.23 (brick houses) as follows:

I saw formal logic and immediately generalized the stimulus as: All Most --> Most

Eliminated three AC's in about 15-20 seconds.

I wrote out the stimulus as:

B F
F 2
B 2

When I went to the AC's, knowing they could be out of order, I put the conclusion as 3, and the "all" statement as 1, leaving me with:

L P
L O
P O

vs.

L P
P O
L O

The choice was so clear and the entire process took me just under a minute, a far cry from the 3-4 minutes I spent missing this question when I took the PT. Perhaps I was a bit greedy by trying to juggle the 'All Most Most' in my head rather than writing it out, but it felt great doing it.

Woo-hoo!

Well done!

[Dave Hall]

57.3.20 (parallel flaw, formal logic)

I spent too long on this question, maybe three or four minutes. I generalized the stimulus as "All, All, Some are not, therefore Some are not." I went to the answer choices and to my dismay, only one actually violates this structure (D) although I didn't notice it at the time.

I then proceeded to diagram the stimulus, followed by (A) wrong, (B) wrong, (C) wrong, (D) wrong, and finally (E) hooray!

Is this question designed to be mean? A parallel flaw question with formal logic that has at least four answers with identical structures and no superficially discerning qualities between them?

Is there perhaps another method I can employ to not stall out here?

I felt just like you did about this one. Just mean, man.

I answered in the same way as you've described. While this wasn't fun (nor particularly fast) it also doesn't have to be totally horrible, if you put a little bit of time in during your practice to become super-fluent with conditional symbols.

Also, 57.2.19 (parallel, formal logic)

I spent maybe three or four minutes on this question as well, but only because I didn't realize that the answer (A --> B ---> C ; A --> C) could be matched by (A --> B ---> C ; ~C --> ~A).

I've never seen this before on another parallel question, if only because it's the sole remaining "packet" of questions by type I've not yet approached. Had I realized this was fine intuitively, I'd have probably cracked this problem in a minute or less.

Are there other questions like this one that anyone has seen, or is this a bit unique in its usage of the contrapositive in this manner?

Thanks for any help!

Good catch! The contrapositive means the same thing as the original statement and is interchangeable with it. This may also help you with a large number of Sufficient Assumption - and also some Inference - questions. Working from memory, I'd say this feature is common to only roughly 10% of Parallel questions (maybe even less).

[Jeffort]

Also, 57.2.19 (parallel, formal logic)

I spent maybe three or four minutes on this question as well, but only because I didn't realize that the answer (A --> B ---> C ; A --> C) could be matched by (A --> B ---> C ; ~C --> ~A).

I've never seen this before on another parallel question, if only because it's the sole remaining "packet" of questions by type I've not yet approached. Had I realized this was fine intuitively, I'd have probably cracked this problem in a minute or less.

Are there other questions like this one that anyone has seen, or is this a bit unique in its usage of the contrapositive in this manner?

Thanks for any help!

The credited response also applies the contrapositive of the premises based on the phrasing used, so the method of reasoning is identical.

The only difference between the argument in the stimulus and the correct answer is a few words with how the conclusions are phrased.

Will not X if not Y
vs.
Will not X unless Y

Those two statements are identical in meaning and logical form.

The conclusions, arguments/method of reasoning applied are logically identical.

Both arguments derive the conclusion from the premises via application of the contrapositive. It's just a slight paraphrasing difference used to state the conclusions. ('unless' used in the correct answer instead of 'if not')

[MLBrandow]

Wow, of course it's the same... I just diagram:

"Not X unless Y" as "If X then Y" but I could just as easily diagram it as the contrapositive of that... My difficulty with this problem was just a result of the construct I've always used from the LRB (If unless, what follows is necessary and negate what precedes it for sufficient condition.) One could just as easily say "draw an arrow on the unless and negate the necessary condition."

That's quite insightful, thanks a lot to you both!

[man_utd_4l]

Currently reviewing PT 42 and I'm looking for a little help on Section 2, problem #18 (Bees and flowers).

I had no problem understanding the stimulus and the concept that the question was asking us to strengthen: that flowers changed in response to bees vision and not vice versa.

I arrived at the credited answer choice (A) through process of elimination, but was wondering if someone could explain the logic behind why answer choice A is credited.

The best that I have been able to come up with so far is that because other insects have similar vision and do not depend on it we can infer that bees also do not depend on it to find the flowers. Thus, strengthening the idea that it is/was the flowers that changed it response to bees.

Thanks in advance!

[Dave Hall]

Currently reviewing PT 42 and I'm looking for a little help on Section 2, problem #18 (Bees and flowers).

I had no problem understanding the stimulus and the concept that the question was asking us to strengthen: that flowers changed in response to bees vision and not vice versa.

I arrived at the credited answer choice (A) through process of elimination, but was wondering if someone could explain the logic behind why answer choice A is credited.

The best that I have been able to come up with so far is that because other insects have similar vision and do not depend on it we can infer that bees also do not depend on it to find the flowers. Thus, strengthening the idea that it is/was the flowers that changed it response to bees.

Thanks in advance!

This question, viewed from one perspective, is quite difficult, but then again, I like it, too, because viewed through a different lens it's pretty conforming. (You see what I'm doing here? I'm BUILDING SUSPENSE).

To Strengthen any argument, we will do so by asserting the assumption of the argument. Here, the causal component of this argument (that bees are the reason for the flowers' colors) involves us in the necessary assumption that there is no other cause of the flowers' coloration.

Answer choice (A) asserts that assumption - if other insects don't depend on color cues, then flower color was NOT caused by other insects' eyes. This doesn't prove that it WAS caused by bees, but it does make it a little more likely, and that's what we were asked to do.

[man_utd_4l]

Currently reviewing PT 42 and I'm looking for a little help on Section 2, problem #18 (Bees and flowers).

I had no problem understanding the stimulus and the concept that the question was asking us to strengthen: that flowers changed in response to bees vision and not vice versa.

I arrived at the credited answer choice (A) through process of elimination, but was wondering if someone could explain the logic behind why answer choice A is credited.

The best that I have been able to come up with so far is that because other insects have similar vision and do not depend on it we can infer that bees also do not depend on it to find the flowers. Thus, strengthening the idea that it is/was the flowers that changed it response to bees.

Thanks in advance!

This question, viewed from one perspective, is quite difficult, but then again, I like it, too, because viewed through a different lens it's pretty conforming. (You see what I'm doing here? I'm BUILDING SUSPENSE).

To Strengthen any argument, we will do so by asserting the assumption of the argument. Here, the causal component of this argument (that bees are the reason for the flowers' colors) involves us in the necessary assumption that there is no other cause of the flowers' coloration.

Answer choice (A) asserts that assumption - if other insects don't depend on color cues, then flower color was NOT caused by other insects' eyes. This doesn't prove that it WAS caused by bees, but it does make it a little more likely, and that's what we were asked to do.

+1

Dave,

Thanks for the quick response time. Your response highlights the type of reasoning that I was hoping this question addressed. It reminds me of a number of other strengthen/weaken questions-46.3.22 (People over 65 in the region) in particular.

Thanks again!

[outlookingin]

Hey experts. I have another kind of huge question here, but maybe it has a simple answer:

How do you treat the relationship between causal, conditional, and formal logic? I'm sure these are all in some ways the same thing but since I've only read the PowerScore Bible I'm using their nomenclature...

So what I'm asking, I guess, is this: what is the overlap between these? How are they different? How should I treat them differently on the test?

My experience so far is that I can diagram formal and conditional logic no problem (just like how PowerScore taught me) but with causal reasoning I just ask the standard questions like "did anything else cause this?" "is this merely correlated?" etc.

Is that an OK approach? I know it's kinda late in the game to be thinking about fundamentals like this but it's been bugging me. Thanks in advance.

[MLBrandow]

Okay experts:

1) A can enable B.
2) A will enable the possibility of B.
3) A can enable the possibility of B.
4) A will enable B.

In which of these statements, if any, can we infer a conditional relationship?

1) nothing
2) A --> possibility of B
3) nothing
4) A --> possibility of B?

An example of this would be in 58.1.13, a question I missed twice mistaking for the credited response a reversal due to "possibility."

Are there other examples of this anyone can recall in other questions?

When I see A --> B, I think "okay if B, then maybe A, maybe not" so I confuse this with "the possibility of A" which I then attribute to the necessary condition. But I can't infer a possiblity of A given B if I only know A --> B, right?

Thanks again for any help!

[man_utd_4l]

Hello Experts,

My question pertains to 53.1.8-Weaken (Night-lights and nearsightedness) in particular and generally to strengthen/weaken questions that have conditionals in their conclusions.

This argument gives us a conclusion that is roughly "If it is the case that X causes Y, the effects disappear with age."

It is my understanding that we want to attack the idea that the "effects disappear with age." However, because the conclusion has a conditional in it we must take the extra step of finding an answer choice that attacks this conclusion while taking the conditional into account. Thus, in this case, we are looking for the answer choice that would attack the conclusion when the sufficient condition (in this case the causal relationship between night-lights and nearsightedness) is true. Is this the correct understanding of this problem?

I understand why D is the credited response in this case. It is a form of the sampling error. I am more concerned with general rules that apply to arguments that use conditionals in their conclusion and then ask us to strengthen/weaken.


*Note I have read the Manhattan Forum responses on this question and watched Dave's video on this problem.*

Thanks in advance!

[Manhattan LSAT Noah]

Off the top of my head, the most common form of what you're asking about is when the causal conclusion that is based on a correlation. There's also conditional conclusions in lots of sufficient assumption questions, which are in effect strengthen questions.

I think you know how to weaken or strengthen causal conclusions based on a correlation premise--show another causal direction is true, or invalidate it. Perhaps I'm not getting what you're saying, but I'm not seeing how those types of answers "take the conditional into account."

For suff. assumption questions with a conditional conclusion, you're finding the missing link, which again doesn't even need to reference the conclusion (though it often does) since the chain's gap can be in an earlier link.

I hope that helps.

[Easy-E]

What this thread made me think of...





If you guys had to offer just one piece of advice for the Logical Reasoning section, something that encompasses your entire approach the section, what would it be? I know that's probably a tough question considering people have written whole books on the subject, but I assume these will be on the general side of things. Thanks!

[Manhattan LSAT Noah]

If you guys had to offer just one piece of advice for the Logical Reasoning section, something that encompasses your entire approach the section, what would it be? I know that's probably a tough question considering people have written whole books on the subject, but I assume these will be on the general side of things. Thanks!

Choose D.

Wait, no, choose E.

[Manhattan LSAT Noah]

If I had to choose one thing, I'd choose two: work wrong-to-right, and, for assumption family questions, boil down the stimulus to the core.

[Easy-E]

If you guys had to offer just one piece of advice for the Logical Reasoning section, something that encompasses your entire approach the section, what would it be? I know that's probably a tough question considering people have written whole books on the subject, but I assume these will be on the general side of things. Thanks!

Choose D.

Wait, no, choose E.

Aw hell I went with B in October! Explains a lot...

If I had to choose one thing, I'd choose two: work wrong-to-right, and, for assumption family questions, boil down the stimulus to the core.

Hmm, would you mind elaborating a bit on what you mean by "work wrong-to-right"? I definitely agree on the second point, those questions become much easier when you simplify them and find the jump in logic. After that, it seems just be a language issue for finding answer choices.

[Manhattan LSAT Noah]

Hmm, would you mind elaborating a bit on what you mean by "work wrong-to-right"? I definitely agree on the second point, those questions become much easier when you simplify them and find the jump in logic. After that, it seems just be a language issue for finding answer choices.

Wrong-to-right is a variant of process of elimination. The difference is that you're actively looking for wrong answers, totally deferring judgement on any answer that seems possibly correct. You do one pass, and then you evaluate what's left, again looking for errors in choices.

Sometimes folks shifting to this attitude can find themselves falling much less often for the trap answers. It's so easy to fall in love with the first pretty answer that walks by...

One caveat: if you're scoring, say 165+ but are finding yourself short on time on LR, the first 7 or so questions should be easy for you and you may need to be more willing to pull the trigger with a less thorough vetting. In those questions, for those test-takers, the right answer should be pretty obvious, and nailing those questions in under 45 seconds is a great way to earn time for the harder, time-consuming questions.

[Easy-E]

Hmm, would you mind elaborating a bit on what you mean by "work wrong-to-right"? I definitely agree on the second point, those questions become much easier when you simplify them and find the jump in logic. After that, it seems just be a language issue for finding answer choices.

Wrong-to-right is a variant of process of elimination. The difference is that you're actively looking for wrong answers, totally deferring judgement on any answer that seems possibly correct. You do one pass, and then you evaluate what's left, again looking for errors in choices.

Sometimes folks shifting to this attitude can find themselves falling much less often for the trap answers. It's so easy to fall in love with the first pretty answer that walks by...

One caveat: if you're scoring, say 165+ but are finding yourself short on time on LR, the first 7 or so questions should be easy for you and you may need to be more willing to pull the trigger with a less thorough vetting. In those questions, for those test-takers, the right answer should be pretty obvious, and nailing those questions in under 45 seconds is a great way to earn time for the harder, time-consuming questions.

Ahh I understand. I guess I do this to a degree, since I try to keep in mind what wrong answers the test will most likely throw at me for question types. I'm at about a 165 average, my current goal is to hit the first 13 in 12 minutes. I pulled this off the last couple times, but I still missed multiple questions in the second half with time to spare, so I guess I just need to use all my time for the last 12 or so. Thanks Noah!

[dowu]

Hmm, would you mind elaborating a bit on what you mean by "work wrong-to-right"? I definitely agree on the second point, those questions become much easier when you simplify them and find the jump in logic. After that, it seems just be a language issue for finding answer choices.

Wrong-to-right is a variant of process of elimination. The difference is that you're actively looking for wrong answers, totally deferring judgement on any answer that seems possibly correct. You do one pass, and then you evaluate what's left, again looking for errors in choices.

Sometimes folks shifting to this attitude can find themselves falling much less often for the trap answers. It's so easy to fall in love with the first pretty answer that walks by...

One caveat: if you're scoring, say 165+ but are finding yourself short on time on LR, the first 7 or so questions should be easy for you and you may need to be more willing to pull the trigger with a less thorough vetting. In those questions, for those test-takers, the right answer should be pretty obvious, and nailing those questions in under 45 seconds is a great way to earn time for the harder, time-consuming questions.

This is great advice. Thank you!

[Dave Hall]

Hey experts. I have another kind of huge question here, but maybe it has a simple answer:

How do you treat the relationship between causal, conditional, and formal logic? I'm sure these are all in some ways the same thing but since I've only read the PowerScore Bible I'm using their nomenclature...

So what I'm asking, I guess, is this: what is the overlap between these? How are they different? How should I treat them differently on the test?

They're like Russian nesting dolls: causal claims are one type of conditional statement, and conditional statements are one piece of formal logic.

So, one thing you may want to begin to do is symbolize causal claims conditionally, in this way:

Cause → Effect

Your approach seems correct, and doesn't necessarily require this adjustment.

[Dave Hall]

Okay experts:

1) A can enable B.
2) A will enable the possibility of B.
3) A can enable the possibility of B.
4) A will enable B.

In which of these statements, if any, can we infer a conditional relationship?

1) nothing
2) A --> possibility of B
3) nothing
4) A --> possibility of B?

Yep. You've got this. As you've noted, 4) is a little tricky; as in the instance you've cited, that A enables one to do thing B doesn't necessarily mean that one will in fact do thing B.

Are there other examples of this anyone can recall in other questions?

Off the top of my head, the only one I can think of is (I think) from an older test; the passage talks about how books allowed for the rise of the traditional school, then erroneously concludes that the death of books would mean death to traditional schools. I know; riveting stuff.

I think the takeaway is that this isn't a huge part of the test.

When I see A --> B, I think "okay if B, then maybe A, maybe not" so I confuse this with "the possibility of A" which I then attribute to the necessary condition. But I can't infer a possiblity of A given B if I only know A --> B, right?

That's exactly right.

[Dave Hall]

Hello Experts,

It is my understanding that we want to attack the idea that the "effects disappear with age."

You know what might help?

Instead of thinking of Weaken questions as asking you to attack the conclusion (which is not a bad way of thinking about them, generally), try thinking of these questions as asking you to attack the purported proof of the conclusion. This is a more accurate representation of the job; you don't have to show that the conclusion is false, you just have to show that it hasn't been proved true.

That, to me, clarifies the relationship of the right answer in this question to the rest of the argument.

Let me know whether that makes sense and whether it helps,

d