## Superprep PT B, Section 1, Question 23

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MissLucky

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Joined: Mon Sep 21, 2009 4:48 pm

### Superprep PT B, Section 1, Question 23

Okay, this question is killing me...

I'm having trouble wrapping my head around why A does not need to be assumed.

I can definitely see how answer choice C is the correct answer, however, where does A go wrong?

If A were false and topsoil erosion DID make farmers want to till more deeply, that would indicate that the argument's evidence has the causality reversed - that when it states "For example, farmers who till deeply are ten times more likely to lose topsoil to erosion than are farmers who use no-till methods", this association exists because having lost topsoil to erosion MAKES farmers want to till more deeply (rather than the other way around as concluded by the argument in the first line in establishing its final recommendation in the last line) and that therefore deep tillage is not the culprit here - that deep tillage is not being harmful to the world's topsoil supply (some other factor is being harmful to it) and the evidence does not prove or indicate anything about deep tillage causing topsoil erosion (since the causality goes the other way if A is negated and thereby shatters the evidence in support of the conclusion).

I hope what I'm saying is clear - let me know if you need me to clarify. Anyways, what am I missing here? What makes A wrong?

Thanks a lot!

yzero1

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Joined: Thu May 27, 2010 4:33 pm

### Re: Superprep PT B, Section 1, Question 23

I think the explanation given by LSAC explains it pretty well.

The issue is that there is no question of whether or not deep tillage causes topsoil erosion. It is clearly stated that deep tillage makes it 10x more likely that a farmer will lose topsoil to erosion. If A is negated, then the chain of causality is two-way - deep tillage causes topsoil erosion which causes even more deep tillage, so on so forth (I think the reason for your mistake is that you assumed that the negation of A would create a one-way causation instead of two-way). What's created is a vicious cycle that results in even more topsoil erosion. This actually strengthens the conclusion that farmers need to avoid this vicious cycle by using other methods.

MissLucky

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Joined: Mon Sep 21, 2009 4:48 pm

### Re: Superprep PT B, Section 1, Question 23

yzero1 wrote:I think the explanation given by LSAC explains it pretty well.

The issue is that there is no question of whether or not deep tillage causes topsoil erosion. It is clearly stated that deep tillage makes it 10x more likely that a farmer will lose topsoil to erosion. If A is negated, then the chain of causality is two-way - deep tillage causes topsoil erosion which causes even more deep tillage, so on so forth (I think the reason for your mistake is that you assumed that the negation of A would create a one-way causation instead of two-way). What's created is a vicious cycle that results in even more topsoil erosion. This actually strengthens the conclusion that farmers need to avoid this vicious cycle by using other methods.

that's definitely my issue. why is it a two-way causation? how do you know FOR sure that deep tillage causes topsoil erosion to start it off? maybe there is something about topsoil erosion that makes farmers want to till more deeply and that's that...i feel like I am missing something really blatant but i cant put my finger on it!

thanks so much btw!

yzero1

Posts: 185
Joined: Thu May 27, 2010 4:33 pm

### Re: Superprep PT B, Section 1, Question 23

You raise a very interesting point and I can see how this can be confusing. I thought about it and I can't really come up with an all-encompassing answer as to why you should assume that deep tilling does in fact cause topsoil erosion (I sort of just assumed it to be so based on the first and second sentences), but I'll do my best to answer your question as to why A can't be the right answer.

Even if you negate A and assume that topsoil erosion makes farmers want to till more deeply, it is still POSSIBLE that deep tillage causes soil erosion. You have to make an EXTRA assumption along with (A) in order to destroy the conclusion - the assumption that the causality only works one way. Thus (A) is not a necessary assumption because negating can still allow the conclusion to follow.

petrovovitch@

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Joined: Wed Jun 16, 2010 12:19 am

### Re: Superprep PT B, Section 1, Question 23

i'll post my initial reasoning before reading your discussion so it doesn't bias me.

the reason why c is the answer is because the assumption is that there are only two choices with respect to what kind of tilling: deep till or no till. they assume that a farmer couldn't adapt medium tilling or shallow tilling instead of deep and keep soil in place.

re:misslucky's initial point

you claim that negation of a would reverse the causality ("that would indicate that the argument's evidence has the causality reversed"). the reverse of the causality is that top soil erosion causes farmer to deep-till, not causes farmers to WANT to deep till. so negation of A does not reverse the causality.

MissLucky

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Joined: Mon Sep 21, 2009 4:48 pm

### Re: Superprep PT B, Section 1, Question 23

petrovovitch@ wrote:i'll post my initial reasoning before reading your discussion so it doesn't bias me.

the reason why c is the answer is because the assumption is that there are only two choices with respect to what kind of tilling: deep till or no till. they assume that a farmer couldn't adapt medium tilling or shallow tilling instead of deep and keep soil in place.

re:misslucky's initial point

you claim that negation of a would reverse the causality ("that would indicate that the argument's evidence has the causality reversed"). the reverse of the causality is that top soil erosion causes farmer to deep-till, not causes farmers to WANT to deep till. so negation of A does not reverse the causality.

this is KEY. man, close reading counts for everything on this test. thank you very much, I see the light now!

MissLucky

Posts: 903
Joined: Mon Sep 21, 2009 4:48 pm

### Re: Superprep PT B, Section 1, Question 23

yzero1 wrote:You raise a very interesting point and I can see how this can be confusing. I thought about it and I can't really come up with an all-encompassing answer as to why you should assume that deep tilling does in fact cause topsoil erosion (I sort of just assumed it to be so based on the first and second sentences), but I'll do my best to answer your question as to why A can't be the right answer.

Even if you negate A and assume that topsoil erosion makes farmers want to till more deeply, it is still POSSIBLE that deep tillage causes soil erosion. You have to make an EXTRA assumption along with (A) in order to destroy the conclusion - the assumption that the causality only works one way. Thus (A) is not a necessary assumption because negating can still allow the conclusion to follow.

aha! very interesting point. another solid reason to discount A. You are absolutely right, the logic does not "depend" on assuming that by any means. even if that answer choice did not have 'want' (see poster after you) and said definitively that "topsoil erosion makes farmers till more deeply", the logic could still presumably hold. in that case, all we would have done is WEAKENED the argument, rather than pointing out a necessary assumption.

Thanks so much you guys those were great points!

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