LSAT Explanation PT 28, S1, Q12: People who say that Dooney County

LSAT Question Stem

The author's conclusion in the passage depends on the assumption that 

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The conclusion of the argument is that Dooney County is not flat. The premises supporting this conclusion are: 1) On flat land, soil erosion by water is not a problem, and 2) Farms in Dooney County are dotted with terraces, which are built to prevent soil erosion.

To make this more understandable, let's use a simple example. Imagine a small town where people only use umbrellas when it rains. If you see someone with an umbrella, you can assume it's raining. Similarly, in the passage, if terraces are built to prevent soil erosion, and there are terraces in Dooney County, we can assume that there is soil erosion and thus, the land is not flat.

An "Evaluate" question for this argument could be: "Are the terraces in Dooney County built for the purpose of preventing soil erosion?"

Now, let's discuss the answer choices. This is a Necessary Assumption question, which means we need to find an assumption that is necessary for the argument to be valid.

a) The argument doesn't depend on the assumption that the only cause of soil erosion is water. Even if other causes of soil erosion exist, the presence of terraces would still indicate that the land is not flat.

b) Correct answer. The argument relies on the assumption that there are terraces on farmland in Dooney County built to prevent soil erosion. If this were not true, the argument would not hold, as the terraces could be built for other reasons.

c) The effectiveness of the terraces in preventing soil erosion is not a necessary assumption for the argument. What matters is the reason they were built, which is addressed in answer choice B.

d) The argument doesn't need to assume that there is no soil erosion on flat land. It only needs to assume that terraces are built to prevent soil erosion on non-flat land.

e) The argument doesn't depend on the assumption that the only terraces in Dooney County are on farmland. The presence of terraces on farmland is enough to support the conclusion that the land is not flat.

In conclusion, the correct answer is B, as it is a necessary assumption for the argument to be valid. The other answer choices can be eliminated because they don't address the core assumption needed to support the conclusion that Dooney County is not flat.