PT68 section 3 #18 (LR)

june2014
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PT68 section 3 #18 (LR)

Postby june2014 » Thu Feb 13, 2014 7:26 am

I got this question right by process of elimination, but I don't really get how it's the correct answer. (E) definitely strengthens the conclusion, but it doesn't seem to be absolutely necessary to the argument since it's possible that the employees can't afford housing within a 30-minute commute of Ocean View even after the pay raise. Doesn't the negation have to destroy the argument in order to be the correct answer to a Necessary Assumption question?

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Christine (MLSAT)
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Re: PT68 section 3 #18 (LR)

Postby Christine (MLSAT) » Thu Feb 13, 2014 12:30 pm

That's a great question, june2014.

The negation test is unfortunately very often misunderstood. To "destroy an argument", the negation of a necessary assumption does not have to make the conclusion categorically false, it merely has to make it unsupported. In other words, the 'destruction' is not so much the conclusion as it is the link between the premise and the conclusion.

Take a crazy simple example:
PREMISE: All boys like sports.
CONCLUSION: Andy likes sports.

This argument is clearly assuming that Andy is a boy. That's necessary to the argument. If we negate it, we get "Andy is not a boy". Now, if Andy is a girl, it is still possible that she likes sports, right? If Andy is a girl, we have NO IDEA about her sports preference, and there would be zero connection between the premise and the conclusion. The conclusion would not be definitively false, but it would be wholly unsupported.

The same thing is going on here. If the move is accompanied by a significant pay raise, then that means we have NO IDEA what they will be able to afford after the move, and making any sort of statement about what they will be able to afford is wholly unsupported.

Does that help?

june2014
Posts: 26
Joined: Fri Nov 29, 2013 7:14 am

Re: PT68 section 3 #18 (LR)

Postby june2014 » Sat Feb 15, 2014 5:43 am

Christine (MLSAT) wrote:That's a great question, june2014.

The negation test is unfortunately very often misunderstood. To "destroy an argument", the negation of a necessary assumption does not have to make the conclusion categorically false, it merely has to make it unsupported. In other words, the 'destruction' is not so much the conclusion as it is the link between the premise and the conclusion.

Take a crazy simple example:
PREMISE: All boys like sports.
CONCLUSION: Andy likes sports.

This argument is clearly assuming that Andy is a boy. That's necessary to the argument. If we negate it, we get "Andy is not a boy". Now, if Andy is a girl, it is still possible that she likes sports, right? If Andy is a girl, we have NO IDEA about her sports preference, and there would be zero connection between the premise and the conclusion. The conclusion would not be definitively false, but it would be wholly unsupported.

The same thing is going on here. If the move is accompanied by a significant pay raise, then that means we have NO IDEA what they will be able to afford after the move, and making any sort of statement about what they will be able to afford is wholly unsupported.

Does that help?



Thank you for the explanation, Christine! So the negation of the correct answer should hurt the unstated link between the premise and the conclusion, and doesn't necessarily need to make the conclusion definitively false? I'm still confused though - whether or not (E) is true, the fact that we have no idea what the employees will be able to afford after the move doesn't seem the change, just like how whether or not Andy is a girl, the conclusion that Andy likes sports is not supported by the premise alone. In this case, how can you tell which one is the answer? Am I misunderstanding/missing something in your explanation?

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Christine (MLSAT)
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Re: PT68 section 3 #18 (LR)

Postby Christine (MLSAT) » Mon Feb 17, 2014 10:38 am

june2014, it's a great question, and I'll think you're opening up the real heart of LSAT arguments right now.

You're absolutely right that the premise in both arguments, by itself, is not enough to fully validate the conclusion. In fact, that's to be expected on almost every LSAT argument - they have to be flawed in some way in order for them to even start asking questions about what the assumptions are, how to strengthen it, etc. Arguments that are perfectly supportable don't have assumptions! So, both before and after a necessary assumption is negated, you're totally correct that we don't know if the conclusion is valid. But there is a difference in what we don't know.

    Before negating necessary assumption: The premise *could* support the conclusion, but we don't know for sure. As a result, we don't know if the conclusion is true, because there is information we are missing.
    After negating necessary assumption: The premise *cannot* support the conclusion, but it's possible the conclusion might turn out to be true for completely unrelated reasons. Whatever support might exist elsewhere in the universe for this conclusion, this premise is not part of it.

Let's return to the Andy/boy/sports argument. The fact that all boys like sports is not enough by itself to fully support the conclusion. It's possible that the premise actually provides support, but only in the scenarios where Andy is likely to be a boy. The more likely it is that Andy is a boy, the more useful the premise is. But the only possible way that this argument could be 'valid' is if Andy is, in fact, a boy.

When we are missing that critical information (as we are originally), the argument is just considered flawed, as it requires additional assumptions to get to validity. But when we *negate* that critical item, the premise can't be used to prop up the conclusion. If Andy is a girl, the statement "all boys like sports" is totally worthless as a support for "Andy likes sports". She might like sports for some totally unrelated reason, but this *argument* (this premise-conclusion pair) is kaput. But all of this debate about the argument is absolutely focused on the link between the premise and conclusion, not just focused on 'can the conclusion be true'. Since the assumption serves as the connective tissue between the premise and the conclusion, it stands to reason that negating the assumption destroys the link rather than destroys the conclusion itself.

Taking all of this discussion into the question you raised: (There are actually a few assumptions here, so I'm going to simplify the core to address only the one we care about.) The argument is using a premise about what employees can afford NOW to support the conclusion that they won't be able to afford that thing in the future. To break that link, all we need to do is say that what they can afford now =/= what they can afford in the future. If that's true, then what they can afford now is irrelevant to the question of whether or not the conclusion could be true.

Does that help at all? I know that a lot of people (myself included) kind of blithely talk about 'destroying the argument', but it is critical to understand that this is a fundamental destruction of the premise-conclusion link, not necessarily a destruction of the conclusion.

june2014
Posts: 26
Joined: Fri Nov 29, 2013 7:14 am

Re: PT68 section 3 #18 (LR)

Postby june2014 » Tue Feb 18, 2014 10:48 am

Christine (MLSAT) wrote:june2014, it's a great question, and I'll think you're opening up the real heart of LSAT arguments right now.

You're absolutely right that the premise in both arguments, by itself, is not enough to fully validate the conclusion. In fact, that's to be expected on almost every LSAT argument - they have to be flawed in some way in order for them to even start asking questions about what the assumptions are, how to strengthen it, etc. Arguments that are perfectly supportable don't have assumptions! So, both before and after a necessary assumption is negated, you're totally correct that we don't know if the conclusion is valid. But there is a difference in what we don't know.

    Before negating necessary assumption: The premise *could* support the conclusion, but we don't know for sure. As a result, we don't know if the conclusion is true, because there is information we are missing.
    After negating necessary assumption: The premise *cannot* support the conclusion, but it's possible the conclusion might turn out to be true for completely unrelated reasons. Whatever support might exist elsewhere in the universe for this conclusion, this premise is not part of it.

Let's return to the Andy/boy/sports argument. The fact that all boys like sports is not enough by itself to fully support the conclusion. It's possible that the premise actually provides support, but only in the scenarios where Andy is likely to be a boy. The more likely it is that Andy is a boy, the more useful the premise is. But the only possible way that this argument could be 'valid' is if Andy is, in fact, a boy.

When we are missing that critical information (as we are originally), the argument is just considered flawed, as it requires additional assumptions to get to validity. But when we *negate* that critical item, the premise can't be used to prop up the conclusion. If Andy is a girl, the statement "all boys like sports" is totally worthless as a support for "Andy likes sports". She might like sports for some totally unrelated reason, but this *argument* (this premise-conclusion pair) is kaput. But all of this debate about the argument is absolutely focused on the link between the premise and conclusion, not just focused on 'can the conclusion be true'. Since the assumption serves as the connective tissue between the premise and the conclusion, it stands to reason that negating the assumption destroys the link rather than destroys the conclusion itself.

Taking all of this discussion into the question you raised: (There are actually a few assumptions here, so I'm going to simplify the core to address only the one we care about.) The argument is using a premise about what employees can afford NOW to support the conclusion that they won't be able to afford that thing in the future. To break that link, all we need to do is say that what they can afford now =/= what they can afford in the future. If that's true, then what they can afford now is irrelevant to the question of whether or not the conclusion could be true.

Does that help at all? I know that a lot of people (myself included) kind of blithely talk about 'destroying the argument', but it is critical to understand that this is a fundamental destruction of the premise-conclusion link, not necessarily a destruction of the conclusion.


So the negation of a necessary assumption must make the premise irrelevant to the truth of the conclusion. I think I get it now. Thank you so much, this was really, really helpful and I really appreciate your explanations!




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