Q25 - Economist: No economic system

[nfagin]

I tried to diagram this, but I do not understand how they derived at the correct answer. Can you please explain this to me?

[aileenann]

No problem.

First, here's my sketch of how I thought the argument worked.

centrally planned -> NO efficient allocation
low nat'l debt -> efficient allocation

Therefore, centrally planned -> NO low nat'l debt

This argument doesn't have a flaw (to see why, form the contrapositive of the second conditional as diagrammed above). Therefore, we want to find a patterned argument that doesn't have a flaw either. We also want to have one that creates a syllogism like this, essentially saying

A -> B
B -> C

Therefore A -> C

Do you see that? Once that makes sense, take a look at these answer choices one at a time, working by process of elimination.

(A) is out of scope - we can see that right away with "not all."

(B) is our answer. To see why, try diagramming, noting that here the final conclusion or end of the logical flow actually comes first:

Rural district -> NO air pollution (C).

because
air pollution -> high conc. autos (1)
rural district -> NO high conc. autos (2)

Here take the contrapositive of (1), combined it with (2), and that will lead you to the conclusion (C).

If you were to see this going through and diagramming out the logical statements, you should pick this answer choice and move on. However, let's take a look at the other answer choices just to make sure.

(C) is out of scope because of the word "most" - our original argument is not talking about "most" but rather all. Notice that (C) is out for the same reason as (A).

(D) This one could be quite tempting, and was probably the runner up in terms of a contender for an answer choice. Because it's tricky, we should think out carefully why it's not correct. Let's diagram logically again:

Famous rock star -> own record co.
Own record co. -> co. profits over reg. royalties.

Therefore, Famous rock star -> LARGE reg. royalties

I have highlighted the word LARGE because it's the whole problem with this answer choice. If that word were gone, this would be a correct answer choice as another illustration of syllogism. However, it just misses the ball with that scope problem.

(E) This one is definitely the confusing one of the lot. On a real LSAT, being so happy with (B), I would probably skip this once I saw how confusing/convoluted it was. However, in practice where we have some luxury of time, it's always a good idea to prove these things out for ourselves. We'll diagram to see whether we can spot a problem:

Mut. fund. man -> knows inside trader
Inside trader -> knows at least one mut. fund. man

We can stop here. We now have two statements that look like
A -> B
C -> D

These statements are not going to link up qua syllogism, so we're done!

I hope this helps. That said, I did use some fancy logic without fully explaining it, so please do let me know if any of this is unclear and needs to be fleshed out a bit more!

#officialexplanation

[nfagin]

Thanks! After I went back and slowly worked out the logic, I picked B as the correct answer. Although my reason for picking B over D was because the original argument used the contrapositive to arrive at the correct answer and so did B, but D didn't. For some reason, I read over and beyond reg royalties to be the same as large regular royalties. But after reading your explanation and re-reading the argument, I see where there was a slight shift in scope that would made the logic incorrect.

[aileenann]

Excellent. I am glad to hear this was helpful. Often, the tricky "wrong" answer will have this subtle sort of scope problem, so keep your eyes peeled.

[mcrittell]

"rural district -> NO high conc. autos (2)"

How do we know to diagram the conclusion as such given the original wording?

[ohthatpatrick]

Good question.

The answer: "because"

"Because" indicates a premise, which means whatever idea it is supporting is some sort of conclusion (either the main conclusion or a subsidiary conclusion).

When LSAT is testing us on conditional logic, it has to give us some trigger words to indicate which claim counts as the conclusion.

Hence, (<--- there's a trigger word there), in Match the Reasoning questions as well as in Sufficient Assumption questions, you'll always see conclusion or premise triggers.

A) "because" indicates that the 1st idea was the conclusion
B) "because" indicates that the 1st idea was the conclusion
C) "It follows" indicates that the Last idea is the conclusion
D) "This implies" indicates that the Last idea is the conclusion
E) "One must conclude" indicates that the Last idea is the conclusion

Conclusion triggers:
Thus, Therefore, Hence, So, Clearly, As a result

Premise triggers:
Because, Since, After All, For

Everyone is good at recognizing Conclusion triggers, but too many students don't see Premise triggers jump out at them. Premise triggers are valuable because they point us to the conclusion.

Consider this example:
Molly is pretty. Therefore, I want to date her.

(easy ... 1st idea is premise, 2nd is conclusion. Now consider the exact same argument, but using premise triggers)

I want to date Molly because she's pretty.
Since Molly is pretty, I want to date her.
I want to date Molly. After all, she's pretty.

On a Main Conclusion question or a Determine the Function question, the test is much more likely to hint at the conclusion via a premise trigger than to be obvious about it and label it with a conclusion trigger.

[mcrittell]

I understood it was a premise, that wasn't my question, but thanks for chiming in anyhow! Got it all clear. Had to parse it out to fig out that the places corresponded to the rural districts.

[lhermary]

I believe E is wrong because of the last bit of the last sentence. 'Unknown to everyone who trades on inside info' doesn't match what the stimulus says "Unknown to every mutual fund manager." Is that correct?

[ohthatpatrick]

I believe E is wrong because of the last bit of the last sentence. 'Unknown to everyone who trades on inside info' doesn't match what the stimulus says "Unknown to every mutual fund manager." Is that correct?

That's definitely part of it. In order to get an airtight syllogism
here (A-->B, B-->C, thus, A-->C), the ideas in the conclusion will have to match up with ideas from the evidence.

As you said, "known/unknown to everyone who trades on insider info" does not have a match in the evidence ... although, you identified the closest contender.

The premises themselves don't connect either, due to language shift problems:

Mut. fund manager --> know someone who T.I.I.

T.I.I --> Known to every mut. fund manager.

None of those four ideas are the same as any other.

Nice work.

[Carlystern]

This is the FIRST I've gotten right on my own!!!!!!!

[pewals13]

Could answer choice (D) be wrong because of the shifting modifiers between the first link and the second link?

Famous rock stars
---->
Own record company

Rock stars with own record company
------>
Receive company profits over and above their regular royalties

Edit: I don't think its an issue because the the condition of being a "famous rock star" would appear to entail the sufficient condition for the second link in the logic chain. If you are a famous rock star, that would automatically entail being a rock star with a record company.

[ohthatpatrick]

Your edit is correct.

However, while we COULD definitely make a chain with the conditionals

Famous RS -> own record company -> receive profits above R's

it would still raise an eyebrow that in the original argument we didn't have to do what we had to do here in (D) (i.e. carry over the trait of "rock star" from the sufficient condition of the first conditional so that we could adequately trigger the sufficient condition of the second conditional).

So your observation is still a worthy red flag. If (D) had actually been an airtight argument, we might have needed that little nuance to distinguish (B) from (D).