#21 - If the law punishes littering, then the city has an

[Administrator]

Complete Question Explanation

Parallel Flaw—Sufficient and Necessary Conditions. The correct answer choice is (D)

As you read the stimulus, you should recognize the conditional reasoning
that pervades this argument. Remember, words such as “if” and “then” are
conditional indicators, and you should pick them up on your LSAT radar
and begin diagramming. In this argument, the first sentence contains a
premise, and the second sentence contains a premise and the conclusion.
The sentences are diagrammed as follows:

     LPL = law punishes littering
     OTC = city has an obligation to provide trash cans

1.PNG

The argument is based on a Mistaken Negation. This is an easy form of
argumentation to identify, and you should feel comfortable attempting to
parallel this structure. Therefore, once you recognize a Mistaken Negation
and read the question stem, immediately search for the answer that also
contains a Mistaken Negation.

Answer choice (A): This answer choice contains a Mistaken Reversal.

Answer choice (B): This answer choice is close to a contrapositive, but
not exactly. There is a time issue between “will be balloons” and “are no
balloons around yet,” and a difference between “her birthday party” and
“her birthday,” results in an imperfect argument. Regardless, this is not
the same error that appears in the stimulus, and so this answer choice is
incorrect.

Answer choice (C): This answer choice contains a Mistaken Reversal.

Answer choice (D): This is the correct answer, and the relationship in the
answer can be diagrammed as follows:

     FL = flight late
     MM = missed the committee meeting

2.PNG

Answer choice (E): This answer choice contains a contrapositive. Because
the question stem asks you to parallel the flawed pattern of reasoning, and
this answer choice contains valid reasoning, this answer choice is therefore
incorrect.

This problem shows that if you can identify the reasoning structure in the
argument, that gives you the best opportunity for moving quickly through
the answer choices. If you quickly find the correct answer, you need not
worry about checking conclusions, premises, etc.

[mbrefo]

Hi,

I have a question regarding answer choice "B."

I thought this answer was mistaken negation because its stated that

Balloons Birthday today

Contrapositive: No Birthday today No Balloons

Conclusion: No Balloons Not her birthday

However, the explanation in the book states this is answer choice is a contrapositive. Am I missing a key word that makes this incorrect?

Please help. Thanks!

[Ron Gore]

Hi Mbrefo,

Thanks for your question!

This is a Parallel Reasoning - Flaw question, and as your question indicates, we are looking for an answer choice containing a Mistaken Negation.

The difficulty you've run into is that your diagram for answer choice (B) is incorrect. That's not surprising, because there aren't any conditional indicator words in the answer choice. Instead, consider the context of the argument. The sufficient condition will be what you see that shows you something else.

In this case, we are essentially given a rule in the first sentence of answer choice (B), that says "Jenny will have lots of balloons at her birthday party." This rule is about Jenny and her birthday party. It is not the presence of balloons that will tell you definitively that it is Jenny's birthday party. Rather, it is Jenny's birthday party that shows you there will be lots of balloons. So, Jenny's birthday party is the sufficient condition, and you would diagram the rule as:

Jenny's birthday party lots of balloons

The contrapositive of this rule is

lots of balloons Jenny's birthday party

If we assume that Jenny's birthday is the same day as her birthday party, which is not necessarily the case, then answer choice (B) contains a valid argument that results from the application of the contrapositive of the rule in the first sentence to the fact that there are not a lot of balloons.

As an aside, be cautious in how you label the pieces of the argument. You say that the conclusion is "no balloons not her birthday." However, what you've labelled as the conclusion is actually partially a premise and partially the conclusion.

Diagrammed out with the premises labelled as "Rule" and "Fact" respectively, the argument is:

Rule: Jenny's birthday party lots of balloons

Fact: no balloons (i.e., not a lot of balloons)

Conclusion: today is not her birthday

Please let me know if you have further questions.

Thanks,

Ron

[mbrefo]

Thank you so much Ron!

[Ron Gore]

You're welcome!

[jonwg5121]

Hi,

I was just curious, is it possible to diagram answer choice (B) as a conditional statement? Thanks!

[Laura Carrier]

Hi jonwg5121,

Yes, you could roughly translate answer choice (B) into a conditional statement if you focus on the relationship it is asserting in its first sentence between the two entities being discussed—Jenny’s party and balloons—and ask what is absolute about it.

When (B) tells us that “Jenny will have lots of balloons at her birthday party,” we have learned something absolute (which will always be true) about Jenny’s birthday party: that there will be lots of balloons. But we haven’t really learned anything equivalent about lots of balloons. Thus, as a result of this sentence, we know with certainty that this conditional relationship exists:

If it is Jenny’s birthday party, then there will be lots of balloons. [JBP LB]

And we definitely don’t have any certainty about this:

If there are lots of balloons, then it is Jenny’s birthday party. [So we cannot say LB JBP]

Thus we can more abstractly represent (B) as having this form:

P1: A B
P2: Not B
C: Not A

Thinking of (B) in these terms makes it possible to definitively dismiss it as an incorrect answer choice, since it contains a correct contrapositive, which fails to match the mistaken negation in the stimulus that you are looking for in your answer choice.

I hope this helps!
Laura

[Johnclem]

Hello,
I got this one right but had a question about C : if we take the second statement of answer choice C ( see below ) it gives us a perfect match for the flaw we encounter in the stimulus . So I guess what I'm trying to ask is .. if a contrapositive of a statment is an identical meaning to its original statement , then why is it wrong to contropose a statement in this case ?

If that was confusing .. sometimes in a must be true or a justify question we can use the contrapositive to prove an answer . Why can't we do the same here ? If we take the contrasposive of C 's second statement , it gives us a match. :-

Stimulus :
Law punishes --> obligation trash cans
Law Does NOT punish --> NO pblogation to have trash cans

C)
Regulation success--> students adhere
Students adhere--> regulation successful


Thank you
John

[Adam Tyson]

Good question, John. If we didn't have answer D as the better answer here (because it perfectly mirrors the Mistaken Negation we found in the stimulus), then we might be able to pick answer C, a Mistaken Reversal, because the two things (MR and MN) are logically equivalent statements.

However, the key here in this Parallel Flaw question is to pick the best answer, the one that matches the most, and that's where D wins out. Think of a standard Parallel Reasoning question, where we want to match the premises and the conclusion. Here, we want to conclude that the necessary condition will not occur based on a premise that the sufficient condition will not occur. Answer C flips that around on us and concludes that a sufficient condition will occur based on evidence that the necessary condition will occur. You are correct that those are equally bad arguments based on the original conditional claims presented, but only one of them matches what happened in the stimulus.

I think there is one other reason to pick D over C, although it may be nitpicking some, and that is the time element. Our stimulus is about the present, as is answer D. Answer C, however, makes a prediction for the future. Not a fatal difference on its own, perhaps, but one more reason to pick D over C.

Ponder that and let us know what you think. Hope that helps!

[lolaSur]

Hi!

I am looking at the additional reading on Lesson 8 of the student center, regarding parallel flaw questions, and this question came up "if the law punishes littering, then the city has an obligation to provide trash cans. But the law does not punish littering, so the city has no such obligation."

I diagrammed the stimulus as follows:
LPL --> T
NOT LPL --> NOT T

Turns out the correct answer is D. I was stuck between choosing D and E and ultimately chose E because I did not consider answer D to have conditional reasoning language. I think the words "in the event that" threw me off, but I see now that "in the event that" just means "if"

Answer D: "In the event that my flight had been late, I would have missed the committee meeting. Fortunately my flight is on time. Therefore I will make it to the meeting"

I realize I could have rephrased this answer choice "if my flight had been late, I would have missed my meeting. My flight is on time, so I did not miss my meeting."

I could have diagrammed answer D as:
FL --> MCM
NOT FL --> NOT MCM

I realize E did not match the conditional form exactly, but I chose E thinking that answer D was not a conditional answer

Answer E: "when the law is enforced, some people are jailed. But no one is in jail. So clearly the law is not enforced"

Diagrammed as follows:

LE --> J
NO J --> NO LE

There is no flaw in the argument presented in answer E