Logical Reasoning

PT144 · S2 · Q9 Two lakes in the Pawpaw mountains

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Two lakes in the Pawpaw mountains, Quapaw and Highwater, were suffering from serious declines in their fish populations ten years ago.

Conclusion

The ban on fishing probably caused the fish population at Quapaw to rebound.

Evidence

Ever since the ban on fishing started, the fish population at Quapaw has recovered, whereas the fish population at the nearby lake, Highwater, has not recovered.

Evaluate

We've got a Curious Comparison, since the author is looking at an asymmetry between Quapaw / Highwater (Q's fish population has been growing, H's hasn't). And the conclusion makes a causal claim because it says "X is probably responsible for Y". So we can use our Curious Fact / Explanation mindset.

Curious Fact ... How come the fishing population has recovered at Quapaw but not at Highwater? Author's Explanation ... The ban on fishing at Quapaw lake is what allowed the fish population to recover.

We should ask ourselves two questions: 1. could there be an Alternate Explanation for the curious fact? why else might the fish be returning to Quapaw lake? Maybe some invasive predator has disappeared. Maybe an algal bloom that messed up the oxygen levels of the water is gone. Maybe someone dumped fish food and live fish into the lake.

2. how plausible is the Author's Explanation? was fishing ever contributing to the decline of fish at Quapaw? Do people like to go fishing there? Since the ban, has there been less fishing?

Conclusion

Since we're Weakening, the correct answer is most likely going to provide some alternate explanation for why fish are recovering at Quapaw but not at Highwater, but it may undermine the plausibility of the Author's notion that .

9.

Which one of the following, if true, most seriously weakens the argument above?

  1. Highwater Lake is in an

    Unclear Impact

    This potentially suggests an alternate explanation for why Quapaw has recovered and Highwater hasn't -- it's not Quapaw's fishing ban that's helping it; it's Highwater's acid rain that's hurting it. The problem is that these two lakes are in the same mountains, so it strains credulity to think that acid rain hits Highwater but not Pawpaw. Generally, lakes in the same mountains would be expected to experience similar precipitation. The fact that this answer also doesn't make any distinction based on ten years ago vs. now makes it less compelling as an alternate explanation. Has Highwater always been susceptible to acid rain? Why was there suddenly a serious decline 10 years ago and why does the fish population continue to decline? This answer definitely weakens somewhat because it raises some suspicion that maybe acid rain is the real explanation for Highwater's low fish count, but it has less impact than the correct answer, which all but refutes the author's proposed explanation.

    18% picked this

  2. Correct

    Prior to the ban, there

    Why this is right

    This makes the Author's Explanation seem thoroughly implausible. This is stronger than (A), because (A) suggests a possible alternate explanation, but (B) basically confirms the author's explanation is probably wrong. because if there was almost no fishing prior to the ban, then how could the ban on fishing possibly be the causal difference-maker that explains why fish are replenishing at Quapaw? In order for something to be a causal difference-maker, there has to be a difference. The author was assuming that, "Now that there is a ban on fishing, there is way less fishing than before, and that's why the fish population is able to replenish." But if there was almost zero fishing at Quapaw before the ban, then there's no way for there to be "way less fishing" after the ban.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

    76% picked this

  3. Highwater Lake is much larger

    No Impact

    This provides a difference, so we can ask ourselves, "Could that difference account for why Quapaw's fish population has been recovering but Highwater's continues to decline?" Is there some common sense link between being a larger lake and not having your fish population recover? No. Maybe a larger lake needs more fish to fill it, but we would probably compare declining population and recovery rates in a relative sense, not an absolute number. (i.e., we would say each lake had lost 30% of its population / we wouldn't count up how many fish). In short, we can't say "the reason that Quapaw is recovering while Highwater is still declining is because Highwater is a larger lake". There's just no common sense bridge from 'larger' to 'not recovering'.

    1% picked this

  4. Several other lakes in the

    Unclear Impact

    Without knowing whether those other lakes also had fishing bans or not, it's impossible to judge the impact. If they did, it would strengthen. If they didn't, it would weaken.

    5% picked this

  5. There used to be a

    No Impact

    This isn't offering an alternate storyline for why Highwater is still on the decline / why Quapaw is recovering. There's no common sense logic to "Highwater isn't recovering yet because that lake used to have more biodiversity". Since the "fish population" is just being discussed in this argument in an aggregate sense, the biodiversity isn't really a relevant concept.

    0% picked this

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