Q25 - The law of the city

[mkeat_theraptor]

I understand that the closest semblance of a correct answer is C. However, this is a must be true question that seems to have a big flaw - it makes a mistake about what can be inferred from a necessary condition!

From what I understand....

>$100 from nonresident -----> must be registered

therefore,

~must be registered -----> ~>$100 from nonresident

The conclusion is that the campaign complied with this law because ~>$100 from nonresident. But because this is a necessary and not sufficient condition, you cannot make any inferences from it! Thus, the CR, ~must be registered does not follow.

If question stated, "Which one of the following allows the conclusion to be properly inferred/drawn?", I could understand. But that's NOT what the questions asks.

The only way I can see that C must be true is if you have a 'if not A then B' scenario. For example,

~>$100 from nonresident = any contribution from any resident, then:

>$100 from nonresident -----> must be registered
AND
~>$100 from nonresident (any contribution from any resident) -----> ~must be registered

But I don't think you can infer this from the language of the stimulus. And without the 'if not A then B' specification, the second conditional chain is a mistaken negation.


What am I missing?

[dan]

Thanks for this question. I have to be honest... I'm not completely following the logic you've laid out. I'm not sure what you mean by "you can't make inferences from a necessary condition." I think you might be overthinking this one by introducing conditional logic in a formal sense. That said, let me write out how I might use conditional logic to think about this question:

The complete extent of the law as it's stated in the passage can be written:

A contribution must be registered if, and only if, it is a contribution of more than $100 from a nonresident who is not a former resident.

The "if and only if" leads to a two-way conditional:

must be registered ---> >100 from nonresident who is not former resident
>100 from nonresident who is not former resident ---> must be registered

The contrapositive of the first conditional is:

~>100 from nonresident who is not former resident ---> ~must be registered

In English, this contrapositive states: If Brimley didn't have any contributions over $100 from nonresidents who are not former residents (which he didn't), then Brimley was not required to register any of his contributions.

This is exactly what (C) states.

Here's the solution I wrote out before reading your question:

The passage clearly states the law as it pertains to campaign contributions in Weston: contributions over $100 made by people who have never lived in Weston must be registered with the city council. If this is the extent of the law (it is stated as such), we can infer that this is the only type of contribution that must be registered. Thus, if Brimley accepted contributions only from residents and former residents, then it must be true that he accepted no contributions that needed to be registered. Answer (C) clearly expresses this.

(A) is not necessarily true. It’s possible that a nonresident who is a former resident of Weston contributed more than $100. Contributions by former residents, even if they are not currently residents, need not be registered (regardless of the amount).
(B) is not necessarily true. Since Brimley accepted contributions only from residents and former residents, he was not required to register any of his contributions, and it’s very possible that he didn’t register any of them (even if they were over $100).
(D) is not necessarily true. It’s possible that Brimley registered all of his contributions (even those under $100), even if he wasn’t required to register any of them.
(E) is not necessarily true. It’s possible that Brimley registered some or all of his contributions, even if he wasn’t required to register any of them.

Let me know if this helps.

dan

[mkeat_theraptor]

I agree that I wasn't sure whether or not this was a conditional dependant question. The language appeared to me consistent with that idea - "all", "must", "only".

If this is a conditional question, it seems to be the opposite of the St. Thomas Aquinas passage Atlas LSAT Teacher posted on TLS in the sense that Q25 seems intuitively logical, but not necessarily formally so.

I agree with your assessment of the qualification 'if and only if' being used to justify what I thought was the stated conditional statement and its contrapositive (which I thought was a mistaken negation.) However, I don't necessarily agree that 'if and only if' can be inferred from the stimulus (this is a special type of formal logic, no?) and therefore I probably should not have tried to justify it using formal logic.

So I guess my dilema is this - given consistent conditional language ("all", "must", "only") how do you determine whether or not it is a formal logic question? And why not, in the case of Q25? I understand that FL questions typically include larger amounts of conditional language, but is that really the only way to distinguish them from questions like Q25?

[noah]

I think the "if and only if" aspect of the question is a way of saying that we can infer (C) because we've been told "the law", so there isn't some other law governing contributions. If we had been told we were reading "a law" it'd be a different story.

As to when to use formal logic notation and when not to, I agree that questions that use a lot of formal logic (conditional statements) can often be more easily torn apart with diagrams. For Q25, I was able to "hold" the whole argument in my mind, and I could evaluate the answer choices against that understanding.

My rule of thumb is that if I can't truly grasp the argument, then I turn to writing out the formal logic. Some folks find that it's useful to write down what they're reading regardless of the "formal-ness" of the question -- I think that's an issue of knowing how you best process what you read.

Perhaps this sounds a bit like silly, but I would not recommend adopting a rule for when to use what sort of attack plan. Test out different ones and see which ones work for you under time pressure. I think you will develop an instinct for this as you practice. One technique is to circle questions that gave you trouble as you do practice tests and then later evaluate if you could have approached it differently.

Good luck!

[dan]

I agree with Noah. I'll add another consideration.

Conditional logic comes up most often on the following question types:

1. Identify a Flaw
2. Application (Match the Reasoning and Match the Flaw)

It is not something that is generally helpful on inference questions (the question you asked about is an inference question). In fact, I don't think I've ever used conditional logic to answer an inference question.

When you've been given a hammer, the temptation is see everything as a nail. In other words, once you've learned about conditional logic, and once you understand the basics, it's tempting to want to hit everything with the conditional logic hammer. Sometimes doing so will overcomplicate this issue.

Once you identify a question as an inference question, immediately put yourself into the inference question mindset:

1. I'm looking for an answer that I can pretty much prove given the information in the passage.
2. I'm actively trying to avoid any answer that requires any additional assumptions.

Again, it's not going to help much to be looking for conditional logic on an inference question (perhaps in a few isolated cases, but not generally).

Hope that helps!

dan

[cyruswhittaker]

Can you clarify why we have the "if and only if" form from the first sentence. Is it due to the "The law" part of the first sentence? If it simply stated "A law," I'm assuming that it would not have this requirement?

[pinkdatura]

Thank you for the explanation. I am a little confused about this "if and only if" So with the opening "THE law" it is "if and only if" relationship but if we start reading after the ":" "all contribution...must be registered with", it seems only a single direction sufficient/necessary relationship.

100+ non-resident,non former resident---> need to register
100+ non-resident,non former resident<---> need to register

So is it "THE law" making the big difference? So subtle and tough...

[perng.yan]

If that is the case.. that it is "if and only if"... then why can't (E) be correct? because you register IF and ONLY IF there is an excess of $100 made by non-residents that were not former residents.

since Brimley had accepted only resident and former resident contributions, it stands that Brimley did not register any contributions with the city council.

[mitchliao]

Can one of the Manhattan LSAT staff please humor me...

I still don't see why "THE law..." makes the statement "No contributions to Brimley's campaign needed to be registered with the city council" must be true.

What if it were the case that: There is a LOS ANGELES city law that states that all contributions of their residents to ANY mayoral campaign MUST be registered to the city council of that city where the mayoral candidate was born. It could be plausible that Brimley was born in the city of Weston. It could also be plausible that a current resident of Los Angeles is a former resident of the city of Weston. And it could be plausible that this specific resident we have been referring to made a contribution to Brimley's campaign.

Then, this specific resident, under the law of the city of Los Angeles, would have to register with the city council of Weston.

Hence, no contributions to Brimley's campign needed to be registered with the city council would not be true.

I guess someone could counter my line of reasoning by stating that it's ridiculous to state that one city (the city of Los Angeles) would require someone to do something in another city outside of their jurisdiction (registering with the city council of the city of Weston). But even if it's 0.00000000001% plausible that what I said above could be the case, then the answer choice (C) is not a must be true.

Is there any apparent holes in my line of reasoning?

Basically what I'm trying to get at is saying that: THE law of Weston automatically destroys the possibility of any other laws in Weston dealing with this subject matter. But, what I'm saying is, THE law of Weston doesn't automatically destroy the possibility of laws OUTSIDE of the city of Weston from coming into play.

[giladedelman]

Thanks for all your posts!

Starting with the last post: I see your reasoning, and I guess it's theoretically possible, although, how would one city force the council of another city to register something, indeed to do anything? So I think your scenario is too far-fetched. Remember, our mindset with inference questions, even ones that say "must be true," is always, What's the most provable inference?

Now as for the "if and only if" issue: I had the same hang-up myself looking at this problem, and only by process of elimination did I decide that (C) was the best answer. It turns out, though, that the wording is everything: we're told that the law "is as follows" -- in other words, this is the law in its entirety. So donations of over $100 from non-/non-former-residents are the only type that need to be registered, since they're the only type named in the law.

If the stimulus instead said, "One aspect of the law is ..." then we wouldn't be able to support (C).

Does that clear this one up for you guys?

[geverett]

Alright, I thought I had seen it all. Apparently I have not. Could it not be conceivable that there is a county, state, etc. law that adds additional requirements?

[giladedelman]

Again, it's hard to imagine how a county or state law or whatnot would require someone to register with the city council. And even if that's conceivably true, (C) is still easily the best answer, so I sleep soundly at night.

[cdjmarmon]

How are yall possibly getting a double arrow if and only if statement out of this thing?

[michael.gorshein]

I assume I'm missing something b/c the logic here doesn't seem right to me.

The stimulus, when it says "the law is...," is basically saying the following:

The only law is that if X -> Y.

(The stimulus is not saying "if X -> Y" and "only X gets Y" ... which would allow you to infer a biconditional.)

How can you infer a biconditional from the statement the only law is that "if X -> Y"?

What it really seems to say is: "if X -> Y" and that there are no other rules... which would leave you not with a biconditional, but only with "if X -> Y".

[ohthatpatrick]

Consider these two statements:

The fruit that Bob likes is apples.

A fruit that Bob likes is apples.

What's the difference in meaning?

The first one indicates that Bob only likes one fruit, and it is apples. The second one indicates that Bob likes apples, and leaves open the possibility that Bob likes other fruits as well.

While the second tells us that Bob likes apples, the first one not only tells us that Bob likes apples but also that Bob doesn't like non-apples.

What's the difference in symbolization?
A fruit that Bob likes is apples =
Apples --> Bob Likes

The fruit that Bob likes is apples =
Fruit=Apples --> Bob likes
AND
Fruit= ~Apples --> ~Bob likes

THAT's how we're getting a bi-conditional.

Normally, from A --> B, we wouldn't be able to infer ~A-->~B.

If we can infer the latter, then we have a bi-conditional.

Let's say we just know this:
A fruit that Bob likes is apples.

Does Bob like oranges?
Maybe so, maybe not.

Let's say we know this:
The fruit that Bob likes is apples.

Does Bob like oranges?
No, he doesn't. Because oranges are a fruit and the (one) fruit that Bob likes is apples.

So saying "the fruit" rather than "a fruit" is more informative. It gives us the ability to make an inference about 'apples' and about 'non-apples'.

I certainly sympathize with everyone's frustration and surprise that LSAT is asking us to appreciate this distinction in Q25. I had the same qualms with picking (C) that others had, because I certainly didn't notice the significance of "the law" the first time I read the paragraph, so I thought that (C) was making an illegal inference. But given that all the other answers had additional speculations/assumptions, I knew that (C) was the best and then figured out that by saying "THE law", the paragraph was implying that no other law exists.

And I would just echo some of the previous sentiments that we might be most successful on this problem my picking the 'most provable' answer, (C), and by avoiding trying to sort out the specific conditional symbolization of the paragraph.

Hope this helps.

[ca_teran1]

Hello,

Why is the set up for conditional statement like this in these posts:
Must be registered---->100 nonresident, contra positive:
-100 from nonresident ---->-not must be registered? ....instead of this way:
$contribution of 100 ---->must be registered nonresident, contra positive: -not registered ---->-100 nonresident?

I say this since the word "all" suggests starting it as an if and it would be if $ is over 100 then...

Please let me know this explanation as soon as possible. Thank you.

[ohthatpatrick]

I'm not sure I totally followed what you typed, but we would symbolize "all contributions in excess of $100 made by nonresidents of Weston who are not former residents must be registered" as

IF more than $100 AND nonresident AND not former resident THEN must be registered.

(I think this is close to what you were suggesting ... as you said, the "all" is a sufficient trigger)

The contrapositive would be

IF it doesn't need to be registered THEN it's $100 or less OR it's from a current resident OR it's from a former resident.

Does that gel with what you were thinking?

[T.J.]

To comply with a law, you do two things: 1. you follow the rules because you are subject to it. 2. you do not really care about the rules because you don't really touch upon the law.

Argument by analogy:
To comply with the gun law, you can do two things: 1. you obtain a permit given that you want to carry the gun. 2. you don't do jack squat, because you never want to carry the gun.

Back to this question:
The campaign complies with the law for the second reason, because the status of residents giving donations excludes it from the conditions of the law.

[db_8400]

I was confused b/w C and E and I focused on "Since it accepted contributions ONLY from residents and former residents of Weston".

To me answer C made sense b/c no contributions needed to be registered b/c ONLY residents and former residents can contribute no one else.

[Smokyearlgrey]

If anyone is still struggling to see why this is bi-conditonal..

I could not grasp this as bi-conditonal as from the beginning, but until after I read the author's conclusion and its implied assumption.

I hope this analogy could help:

International NASA policy
if aliens come to earth ➔ aliens reports to NASA headquarter in person (no pun intended)

This NASA policy would be complied if either
Sufficient condition is met and Necessary condition is also met OR
sufficient condition is not met, thereby making the policy irrelevant.

S ✓➔ N ✓
S X ➔ N ?

The only way it can the policy can be breached is by having the sufficient condition while necessary denied

S ✓ ➔ N X


So the authors conclusion is something to the effect of:

There are only humans in this galaxy. (There are no alines!) Obviously the NASA policy would not have been broken because this is within the context of

S X ➔ N?

So, what is the truth value of Necessary condition in this case? usually the necessary value in this equation would be one of uncertainty.
However, the context makes this Necessary condition negated. Why?

if Necessary condition is positive that means [aliens reports to NASA headquarter]. But how can they report to NASA headquarter unless they come to earth? so there is an underlying assumption to the context that actually makes

if aliens come to earth ➔ aliens report to NASA headquarter in person (➔ if they report to NASA headquarter in person they have come to earth)

this would make this relationship bi-conditonal.

In comparing with the answer choice (C), this would be something like
Given that there are no aliens, it must be true that no aliens needed to report with the NASA headquarter (because aliens did not come to earth)

I hope my analogy helps. If i am wrong please correct me!

Best,