PT46.S3.Q24 - editorialist: despite the importance

logicfiend

https://7sage.com/lsat_explanations/lsat-46-section-3-question-24/
This sufficient assumption question really has me thrown. I've read the Manhattan explanations on this, but I'm still having a hard time with understanding the whole question.

Conclusion: Money doesn't exist.

Why? The only thing you need for money to disappear is a universal loss of belief.

Gap seems to be that because something disappears it doesn't exist.

So Manhattan represented this in conditional logic as:

(loss of belief --> disappear) --> NOT exist

Easy enough, although it wasn't my instinct to put loss of belief as the sufficient condition. Still, with this conditional logic, I think I understand how (A) is the correct answer as the contrapositive.

Exist --> NOT (loss of belief --> disappear)

My problem is I'm having a hard time understanding what the necessary condition is saying here. What does NOT (loss of belief --> disappear) actually mean? Something can exist even if there isn't a loss of belief and it doesn't disappear? Also confused about how this works as a sufficient assumption answer, how does this prove that money doesn't exist? Any help?

As a side note, has anyone seen this conditional logic set up in other questions I can look at?

c.janson35

Hey LogicFiend! The necessary condition above seems more like something that would be found in a truth table. Based on the assumption that NOT is similar logically to FALSE (because if something is not the case, then it is false), we can infer some things. If a conditional relationship, say A-->B, is false, then it is the case that A obtains and B does not. This is the only way that relationship could be false. So, NOT (loss of belief--->disappear) would mean that a loss of belief occurred but something did not disappear.

BUT... this isn't necessarily helpful and actually makes the stimulus more abstract. I think the best way to do this problem is to try to anticipate what the correct answer would be by identifying the gap in reasoning, which you did nicely. There is a jump from loss of belief and disappearing to not existing. So, in order to prove this question, we have to connect these ideas.

This is actually a simple A-->B argument template at its core.
A-->B
A
------------
B

What are the two variables we know?
P:Money would disappear if there was a universal loss of belief in it
C:Money does not exist.

So, how do we prove the conclusion with the premise? Well, if we assumed there was a conditional relationship between them. Thus, A would be "Money would disappear if there was a universal loss of belief in it" and B would be "Money does not exist". That means the sufficient assumption that would prove our conclusion is (drum roll)....

A--->B
If something disappears because of a loss of belief in it, then that thing does not exist.

This would 100% prove our conclusion. Because LSAC is sneaky though, they put the correct answer in terms of its contrapositive:

CP: If something exists, then that thing would not disappear because of a loss of belief.
This is roughly what A says!

Hope this helps!


Pro tip PS: this question is abstract and confusing, but it can be made easier by just knowing what the gap is and what variables you need to connect. The only answer that comes close to this is A, and everything else can be quickly eliminated by POE.

B: mistaken beliefs? that adds a new variable. eliminate
C: practical consequences? another new variable, and not what we are looking for.
these are roughly our 2 variables, but we are concerned with what happens if everyone does not believe in something, and this is about what happens if everyone believes in something. Not what we want. Eliminate
E: financial markets generally LOL. Definitely not what we are looking for. You would't prove the conclusion by talking about the analogy. Eliminate quickly.

logicfiend

This is very helpful, I think I was making it more complicated—rough question though. Thanks!

stephaniexen

Premise 1: "the fact that all that would be needed to make money disappear would be a universal loss of believe in it."

universal loss of belief --> money disappears

Premise 2: "fluctuations are the result of mere beliefs of investors"

investors' beliefs --> fluctuations (i.e. money disappears and comes back)

From the two premises:

universal loss of belief --> money disappears
investors' beliefs --> money disappears

We can say: Regardless of people's beliefs, money disappears. If everyone loses belief (universal loss of belief), it disappears. If they do believe (like investors), it fluctuates, temporarily disappearing. Thus, we can accept "Money disappears" as a fact:

A --> B
Not A --> B
-----------
Thus: B

Now the editorialist's conclusion is: Money does not exist.

So the sufficient assumption the stem requests is:

money disappears --> money does not exist

Notice, this leads to the contrapositive:

money exists --> money does not disappear

To reiterate, in plain English: If money exists, then money doesn't disappear, even if people do not believe it.

Compare answer A: "Anything that exists would continue to exist even if everyone were to step believing in it."

This answer sufficiently guarantees the arguments validity (since "anything" would obviously include money.)

The key here is the phrase "even if". "A even if B" means "A regardless of B" or "A whether or not B". This reiterates our inference above: (A --> and (Not A --> , thus B.