LSAT 141 – Section 2 – Question 20

LSAT 141 - Section 2 - Question 20

September 2014

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Question QuickView	Type	Tags	Answer Choices	Curve	Question Difficulty	Psg/Game/S Difficulty	Explanation
PT141 S2 Q20	+LR	Necessary assumption +NA Causal Reasoning +CausR Link Assumption +LinkA	A 10% 161 B 5% 159 C 4% 154 D 32% 160 E 50% 166	153 163 172	+Hardest	146.882 +SubsectionMedium

J.Y.’s explanation

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The advent of chemical fertilizers led the farmers in a certain region to abandon the practice of periodically growing a “green-manure” crop, such as alfalfa, in a field to rejuvenate its soil. As a result, the soil structure in a typical farm field in the region is poor. So to significantly improve the soil structure, farmers will need to abandon the use of chemical fertilizers.

Summary

The author concludes that to significantly improve soil structure, farmers will need to stop using chemical fertilizers.
Why does the author think this?
Because the introduction of chemical fertilizers led farmers in the region to stop the practice of periodically growing a “green-manure” crop for rejuvenating the field. The stopping of this practice led to damage to the soil structure.

Notable Assumptions

We know that the introduction of chemical fertilizers caused, in this one case, farmers to stop growing “green-manure” crops. And this damaged soil structure. But does this prove that in order to improve the soil structure, we need to abandon the use of chemical fertilizers? No — why couldn’t we just get the farmers to start growing “green-manure” crops again? The premises never established that we can’t use both the chemical fertilizers and grow “green-manure” crops.
The author is assuming that we can’t use both — that in order to get farmers to grow “green-manure” crops again, we have to stop using chemical fertilizers.

most, if not all, farmers in the region who abandon the use of chemical fertilizers will periodically grow alfalfa

Not necessary, because alfalfa is just one example of a “green-manure” crop. But other “green-manure crops” could be grown instead. Also, the author doesn’t need to assume that “most” farmers will grow crops. As long as enough farmers grow the crops to improve soil structure, the reasoning still works.

applying chemical fertilizers to green-manure crops, such as alfalfa, has no positive effect on their growth

Not necessary, because even if chemical fertilizers have a positive effect on “green-manure” crop growth, it could still be necessary to abandon their use in order to get farmers to grow “green-manure” crops again.

the most important factor influencing the soil quality of a farm field is soil structure

The argument concerns what’s required to improve soil structure. Whether soil structure influences other things, such as soil quality, is not relevant to the argument. And even if it were, there’s no reason the author must assume that soil structure is the “most” important factor in soil quality.

chemical fertilizers themselves have a destructive effect on the soil structure of farm fields

Not necessary, because the effect of chemical fertilizers was to cause farmers to abandon “green-manure” crops. Even if the chemical fertilizers do not directly destroy the soil structure, they still had the effect of causing abandonment of the practice that rejuvenated soil structure.

many, if not all, farmers in the region will not grow green-manure crops unless they abandon the use of chemical fertilizers

Necessary, because if it were not true — if many farmers in the region WILL grow “green-manure” crops even if they keep using chemical fertilizers — then there’s no reason farmers would need to stop using chemical fertilizers to improve the soil structure. They could keep using the fertilizers and start growing the crops again.

If you're having trouble deciding between (A) and (E), here's a very subtle hint.

Think about the grammar.

In terms of grammar, (A) is subject dense and (E) is predicate dense. In other words, the subject of (A) is heavily modified whereas the predicate of (E) is heavily modified.

The main subject of (A) is farmers. All farmers? No. It zooms in onto a subset of all farmers called farmers in the region. All of those? No. It further zooms in onto a subset of all farmers in the region who abandon the use of chemical fertilizers. All of those? No. It further zooms into a subset of those called "most". Okay, now that we've finally got the right zoom level, those farmers, what about them? What's the predicate? Well, just that they will periodically grow alfalfa.

Contrast that with (E). The subject is "some farmers in the region". In other words, at least one farmer in the region. What about them? (What's the predicate?) It's complicated. It's a conditional predicate. We're saying for at least one farmer in the region, the follow is true: if they grow green-manure crops, then they abandon the use of chemical fertilizers. In other words - remember your lawgic / translation lessons - their growing green-manure crops depends on their abandoning their use of chemical fertilizers.

Can you negate this statement?

When I say for some people, X is true, the negation of that is for no person is X true. (Review this lesson.) And that means for all persons, X is not true. (No dogs like to eat salmon = all dogs do not like to eat salmon.) So apply that here. For no farmer in the region is growing green-manure crops dependent on their abandoning use of chemical fertilizers. That means for all farmers in the region, not[growing green-manure crops dependent on their abandoning use of chemical fertilizers]. Remember how to negation conditional statements? Negated, the statement is that growing green-manure crops can happen alongside with not abandoning (that means continuing to use) chemical fertilizers. For all farmers in the region, that's true.

LSAT 141 – Section 2 – Question 20

LSAT 141 - Section 2 - Question 20

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J.Y.’s explanation

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LSAT PrepTest 141 Explanations

Section 1 - Reading Comprehension

Section 2 - Logical Reasoning

Section 3 - Reading Comprehension

Section 4 - Logical Reasoning

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