Logical Reasoning

PT143 · S3 · Q25 The populations of certain species

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The populations of certain species of amphibians have declined dramatically in recent years, an effect many scientists attribute to industrial pollution.

Conclusion (therefore)

It's impossible to be sure that the recent decline in those amphibian populations is due to industrial pollution.

Evidence

Most amphibian species' populations vary greatly from year to year because of natural variations in the weather.

Evaluate

The Linking assumption for this argument would just be "If Premise, Then Conclusion": If most populations of a group of species vary greatly from year to year due to weather, then it's impossible to be sure that any decline is due to pollution.

Since that seems like an unlikely answer, we should probably shift into Objection mode, trying to think of a weakening idea that the correct answer might rule out (a Defender style answer).

Given that ... most amphibian populations vary greatly from year to year because of natural variations in the weather,

How could we say that ... it is possible to be sure that this recent decline in certain amphibian populations is due to industrial pollution?

Maybe we could say that the recent declines don't resemble the sort of declines that are caused by natural variations in the weather -- they're way steeper / they happen at the wrong time of the year / they accelerate at a much faster pace / etc.

Maybe we could say that these declines happened right after the industrial pollution started. They stop happening whenever pollution is lighter. They basically ebb and flow in perfect tandem with industrial pollution.

Goal

We might see an answer linking "natural variations from year to year" with .

But more likely we'll see an answer that, if negated, turns into an objection. Whenever we're anticipating a Defender type answer, we're especially tantalized by answers that are ruling out an idea with wording like "not / no".

25.

The argument depends on assuming which one of the following?

  1. Correct

    The amphibian species whose population

    Why this is right

    Whenever we're doing Necessary Assumption and see an answer choice ruling out an idea, using "not / no" language, we get very enticed. We want to negate these and see if they turn into objections. negation: the amphibians whose population declines have been attributed to pollution are known to be among those species whose populations do not vary greatly from weather. Does this weaken? Sure! The author is saying, "we can't be sure if the populations of these certain amphibians are declining because of industrial pollution, because most species of amphibians have rising and declining populations due to variations in weather". He's assuming that the amphibians we're talking about belong to that majority category. If these certain species are known to be species whose populations don't vary greatly from year to year from weather variations, then the author's solitary premise is completely irrelevant. It would be like if someone argued, "Some people think Tom wasn't at school because he was sick. However, most students miss days periodically because they are on extracurricular teams that travel for events at other schools. It is thus impossible to be sure that his absence was due to illness". This argument is assuming that Tom is on an extracurricular team. If it's known that he is not on an extracurricular team, that would badly weaken the argument, because the only premise for doubting that he's sick is this notion that he might be on an extracurricular team traveling for an event. If that alternate explanation isn't applicable to Tom, then the author hasn't presented any reason to doubt his illness. Similarly, if the amphibians that many scientists think are dying from industrial pollution are known to not be amphibians whose population numbers rise and fall with weather variations, then this author has no case!

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

    61% picked this

  2. The variations in amphibian species'

    Weakens

    This actually sounds like one of our objections: what if the declines in population we're trying to explain are very different in size or type from the typical declines in population caused by variations in weather? If we negate this answer, it becomes a Strengthen idea -- the variations in population resulting from weather are always as large as the declines scientists have attributed to industrial pollution. This negation makes the author's suggested Alternate Explanation seem much more plausible.

    8% picked this

  3. Either industrial pollution or natural

    Too Strong

    Too Strong: X or Y but not both The author isn't making any positive claims about what did cause the declining population, so there's no way we can accuse her of thinking, "The only options for what caused it are purely weather or purely pollution." If we negated this answer, it would be saying, "It's also possible that the declining population is caused by a mix of weather and pollution. It's also possible it's due to some other factor we haven't yet named." That would actually strengthen the author's argument. The more possible causes (or combinations of causes) there are that could potentially explain this decline in population, the more apt we are to believe the author's conclusion, that "it's impossible to be sure that the recent decline is from the pollution".

    24% picked this

  4. If industrial pollution were reduced,

    Opposite, if anything

    This author is arguing that we have no idea whether pollution has caused these population declines. Meanwhile, this answer sounds like someone who is utterly convinced that pollution is causing the population declines. Someone who's convinced that pollution causes decline would believe that "if less pollution, less decline" and "if more pollution, more decline". Our author would be like, "If industrial pollution were reduced, who knows what would happen? After all, we have no idea whether the recent decline in population is due to pollution in the first place!"

    3% picked this

  5. If industrial pollution is severe,

    Out of Scope: severe

    We never talked about different gradations of industrial pollution, so as soon as we see this answer is saying, "If industrial pollution is severe", we can stop reading. We have no idea what this author thinks happens under such specific parameters.

    4% picked this

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