Q21 - If the law punishes littering

[sonya76k]

Hello -

Could you please explain the difference between answer choice B and D, and why D is the correct answer? Thank you!

[csunnerberg13]

Hello -

Could you please explain the difference between answer choice B and D, and why D is the correct answer? Thank you!

So here's a breakdown of this question, which is made up of conditionals - so diagramming is very helpful.

The stimulus says:
LPL --> CO
-LPL --> -CO

key:
LPL = law punishes littering
CO = city obligated to provide trash cans

The flaw here is illegal negation - you can't just negate both sides of the conditional statement, that's an incorrect inference. So that's what we want to happen in our answer choice too.

(A) tells us
H --> -B.
-B --> -H.
Incorrect but not for the same reason as the stimulus.

(B) tells us
Jenny's Party --> Lots of balloons.
-Balloons --> -Jenny's Birthday
There are all kinds of mismatches here, so that's a pretty big clue it's not the right answer when our original allowed us to make 2 definitive conditionals. This flaw doesn't match our original, either.

(C) tells us
RS --> SA
SA -- RS
This is another common flaw - illegal reversal - but again, not the flaw we are looking for.

(D) tells us
FL --> -C
-FL --> C
This matches exactly our stimulus by simply negating each side of the second statement. That's the flaw we are looking for and this is the correct answer.

(E) tells us
LE --> Some J
-J --> -LE
Be weary of the "some" in this statement - no "some" in our original. That doesn't totally rule it out as an option, but when you look closer there's another issue too. It's actually a correct contrapositive of that statement, so there's no flaw here and therefore that could never be the answer to a "match the flaw" question.

Hope this helps

[Carlystern]

Hello -

Could you please explain the difference between answer choice B and D, and why D is the correct answer? Thank you!

So here's a breakdown of this question, which is made up of conditionals - so diagramming is very helpful.

The stimulus says:
LPL --> CO
-LPL --> -CO

key:
LPL = law punishes littering
CO = city obligated to provide trash cans

The flaw here is illegal negation - you can't just negate both sides of the conditional statement, that's an incorrect inference. So that's what we want to happen in our answer choice too.

(A) tells us
H --> -B.
-B --> -H.
Incorrect but not for the same reason as the stimulus.

(B) tells us
Jenny's Party --> Lots of balloons.
-Balloons --> -Jenny's Birthday
There are all kinds of mismatches here, so that's a pretty big clue it's not the right answer when our original allowed us to make 2 definitive conditionals. This flaw doesn't match our original, either.

(C) tells us
RS --> SA
SA -- RS
This is another common flaw - illegal reversal - but again, not the flaw we are looking for.

(D) tells us
FL --> -C
-FL --> C
This matches exactly our stimulus by simply negating each side of the second statement. That's the flaw we are looking for and this is the correct answer.

(E) tells us
LE --> Some J
-J --> -LE
Be weary of the "some" in this statement - no "some" in our original. That doesn't totally rule it out as an option, but when you look closer there's another issue too. It's actually a correct contrapositive of that statement, so there's no flaw here and therefore that could never be the answer to a "match the flaw" question.

Hope this helps

I don't understand how the above set up of the stimulus matches (D) set up.

Is it because each side has a like term negated?

[maryadkins]

I don't understand how the above set up of the stimulus matches (D) set up.

Is it because each side has a like term negated?

Yep!

Thanks for the explanation, Elle Woods. Great job.

Only thing I want to add is that on Answer Choice (C), "most" is a problem"”we don't diagram that as a conditional, period (like (E)). It therefore doesn't match the stimulus. But if we removed the "mosts" and diagrammed it as a conditional, Elle's explanation would be correct.

[WaltGrace1983]

I don't understand how the above set up of the stimulus matches (D) set up.

Is it because each side has a like term negated?

Yep!

Thanks for the explanation, Elle Woods. Great job.

Only thing I want to add is that on Answer Choice (C), "most" is a problem"”we don't diagram that as a conditional, period (like (E)). It therefore doesn't match the stimulus. But if we removed the "mosts" and diagrammed it as a conditional, Elle's explanation would be correct.

I'm a bit confused as to why that would be. As I understand it (though I am probably wrong), the "most" or "some" is not so much the problem as is the way the argument is structured.

The original argument is basically:
A → B
~A
Therefore, ~B

Let's say I said the following: "if most people in Cleveland believe that the Cavaliers will win the championship, the Cavaliers definitely will win. However, most people in Cleveland actually do not believe this. Thus, the Cavaliers will not win."

Because of the structure of this argument, the "most" is not really the same as saying "Most A's are B." Instead, the "most" is really just alluding to the percentage of Clevelanders that have to believe. My above example could still be diagrammed as A → B, ~A, Therefore ~B, correct?

This is the same thing I am seeing with (C) and (E).

(C): Successful → Most Adhere, Most Adhere, Therefore (Successful)

(E): Enforced → Some Jailed, ~(Some Jailed), Therefore, ~Enforced. This is actually valid I do believe.

Anyway, that is my (probably incorrect) thought process. Is there something I am not doing correctly because I'd like to make sure my understanding is okay!

[maryadkins]

Because of the structure of this argument, the "most" is not really the same as saying "Most A's are B." Instead, the "most" is really just alluding to the percentage of Clevelanders that have to believe. My above example could still be diagrammed as A → B, ~A, Therefore ~B, correct?

This is the same thing I am seeing with (C) and (E).

Ooooooh, nice catch! I missed that, somehow. My bad! Good note. I revise my earlier statement accordingly!

So (C) is wrong, because in the stimulus you have:

A --> B
~A --> ~B

But (C) is, interpreting "most" the way you are, by looping it into the conditional:

A --> B
B --> A

It's a different flaw (as noted earlier in this discussion).

And agreed that (E) is valid:

A --> B
~B --> ~A

Thanks for pointing that out, Walt!

[stacksdoe]

If I may add:
During the actual test though, because time is at the most importance, you could just easily eliminate (C) and (E) because they are talking about "most" and "some" respectively. No where in the fact pattern-stimulus- are we presented with "most" and "some", so (C) and (E) are clearly wrong.
I had trouble with this question, and I went with answer choice (B) because it was the only one I couldn't rule out. But after digging deeper, I found my mistake. We can't go from lots of balloons in the premise to talking about just "balloons", it's not the same thing. Further more, (B) just doesn't not have the same "mistaken negation" aka incorrect reversal as the stimulus, as pointed out by earlier posts.

[egonza14]

Hi, I know this question hasn’t been touched in years, but I just had a more fundamental question about the logic being used here.

While I know what an illegal Negation and an illegal reversal look like at face value and can easily recognize one while doing questions (I knew there was an illegal negation in the stimulus), I got tripped up on this question because of the abstract wordings that I’ve seen used to describe these flaws in the correct answer choices on Flaw questions. I could be completely wrong here, but don’t both flaws describe mistaking the Necessary and Sufficient conditions for each other?

The reason I got this question wrong was because I have been operating with that possibly misperceived shared bond between the two flaws, so I immediately circled answer Choice A) on this Q then moved on. In review, D) is a CLEAR illegal negation, so I had an “uh oh” type of epiphany.

So briefly then, Has my above understanding of the relationship between these two flaws been wrong this whole time, or is it just that on Match the Flaw Questions that they want that exact match?

[ohthatpatrick]

You're understanding is correct.

An illegal reversal / negation are the same thing: the Conditional Logic flaw, aka "Necessary vs. Sufficient"

And on Matching questions they almost never make us pick between two flaws that are functionally the same. But once in a rare while, they do, and tie goes to the one that more closely matches the order/structure of the original.

LSAT could be nuanced and say (A) and (D) are the same flaw, but (D) is the more similar flawed pattern?

On the other example of this that I can think of, it's a match the flaw question stem that says something like, "the flawed pattern of reasoning above can most effectively be demonstrated by similarly arguing ..."

Again, the question stem allows you to say that an answer like (D) is superior to an answer like (A), because it's EASIER to demonstrate the flawed logic of the original if you match it's exact order and structure.

On Matching, we can usually gamble on picking the first answer that works. But once is a rare while, two answers "work", but one is more identical to the original.