PrepTest 156

[lcid:3723] Prep Test 156 LSAT — Logical Reasoning — S4 Logical reasoning

Question prompt

Ecologist: El Niño, a Remaining source text redacted.
Why the credited answer is right

Credited answer: D

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Valid or Flawed

Flawed

Strategy Overview

Argument or facts? Always argument, so identify premises and conclusions of argument Anticipate why the premises are not enough to show that the conclusion is true
Causal argument? Look for answer choice that:
Shows possible alternate cause Shows cause without effect Shows effect without cause Shows the cause and effect are reversed
If not causal argument, anticipate ways to worsen problem with argument
Use anticipations to select the answer choice that, if true, would weaken argument

Answer Anticipation

Our ultimate goal is to find the answer choice that weakens the argument. However, it's much easier to do that if we first break down the argument and identify its flaws. Then, weakening the argument is only a matter of finding the answer choice that exploits that flaw. Causation flaws are the most common issue on these questions, so experienced test-takers look for that flaw first. Although the premises express several cause-and-effect relationships, the conclusion does not. So, this argument doesn't commit a causation flaw. However, after breaking down this argument, an experienced test-taker would probably notice the "concept switch" that occurs between the last two premises. We know that El Niño causes heavy winter rainfall in region T. We also know that rodent populations typically increase during "long periods of sustained rain." The ecologist assumes that "heavy winter rainfall in region T" and "long periods of sustained rain" are effectively the same concept. However, these concepts may be different. "Heavy winter rainfall in region T" may, in fact, just sporadic rainfall that isn't sustained over a long period. In that case, El Niño probably won't increase region T's rodent population in the coming decades. So, the correct answer will probably weaken the argument by exploiting this problem. We can look for an answer choice that says that heavy winter rainfall in region T isn't sustained over a long period of time.

Answer choices

  1. A
    In region T, there Remaining source text redacted.
    Why choice A is not credited

    This doesn't weaken the argument. Even if there's much less rainfall in region T during the summer, El Niño will still increase rainfall during the winter. If this rainfall is heavy enough and sustained enough to increase rodent populations, we can expect the rodent population in region T to increase.

  2. B
    Rodent populations in region Remaining source text redacted.
    Why choice B is not credited

    This strengthens the argument by reinforcing the relationship between heavy rainfall and rodent populations. The ecologist assumes that long periods of heavy rain cause rodent populations to increase. One way to strengthen a cause-and-effect relationship is by showing "no cause, no effect." This entails showing that if there's no cause present, the effect won't follow. This answer choice does just that, establishing that a lack of heavy rain (no cause) means that the rodent populations will decrease (no effect).

  3. C
    In many regions that, Remaining source text redacted.
    Why choice C is not credited

    This answer choice is tempting, especially if you were looking for one of the common causation flaw weakeners. This answer choice is structured to resemble "cause without the effect" since it shows that in many plays where the cause is present, the effect is not.

    However, there are a few reasons why this answer choice doesn't weaken the ecologists' argument. First, this answer choice uses weak, wishy-washy language ("many") that we don't like in Weaken questions. Even if there are examples of "cause without the effect" in "many regions," the vast majority of regions could exhibit a strong, positive correlation between rainfall and rodent populations.

    Second, the answer choice doesn't really supply the "cause," so it's not truly an example of "cause without the effect." The ecologist assumes that long periods of sustained rainfall cause rodent populations to increase. These other regions may experience heavier rainfall than region T, but that doesn't mean that this rainfall is sustained over a long period of time.

    Finally, the ecologist assumes that rodent populations increase in a given region during long periods of sustained rainfall. The ecologist doesn't assert that rodent populations will be larger in regions with long periods of sustained rainfall than in regions without such rainfall. So, even if region T already has more rodents than these other regions, El Niño could still increase region T's rodent population.

  4. D
    In region T, winters Remaining source text redacted.
    Why choice D matches the stem

    As expected, this weakens the argument by establishing that heavy winter rainfall in region T isn't sustained over a long period. So, even if El Niño causes heavy winter rainfall in region T, this rainfall will not be sustained for a long enough to increase region T's rodent population. This undermines the author's conclusion that region T's rodent population will probably increase in the coming decades.

    Since this answer choice matches our anticipation, we can justifiably select and advance to the following question.

  5. E
    The global warming caused Remaining source text redacted.
    Why choice E is not credited

    This is another tempting answer choice that is structured to look like an "alternative cause," one of the common causation flaw weakeners. This answer choice would weaken the argument if we knew that global warming produces other effects in region T that could decrease rodent populations. In that case, these effects might cancel out El Niño's effects on region T's rodent population.

    However, as written, this answer choice doesn't say that global warming produces other effects in region T or that these effects would decrease region T's rodent population. It's possible that global warming's alternative effects don't occur in region T. It's also possible that these effects increase its rodent population, which would further support the ecologist's conclusion.

    Since we can't definitively say that this answer choice would weaken the ecologist's argument, we must eliminate it.

Discussion

No threads yet—be the first to ask a question or share an approach.

View all discussions Start a discussion