Logical Reasoning

PT152 · S2 · Q11 Last year the Lalolah River

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Last year the Lalolah River was ranked by the Sunvale Water Commission as the most polluted of the fifteen rivers in the Sunvale Water District.

Conclusion (must be = causal speculation)

Measures taken to clean up the river must be working.

Evidence (since)

This year the Lalolah River is ranked as only the 3rd most polluted river in the district.

Last year it was ranked #1.

Evaluate

This argument has a common structure. The evidence is an Asymmetric Comparison (it used to be ranked 1st most polluted, but now it's ranked 3rd most polluted).

And the author's conclusion states or assumes a causal explanation for that Curious Fact, that asymmetric comparison.

Curious Fact .... Why did the river go from being the most polluted to the 3rd most polluted?

Author's Explanation .... they took some measures to clean up the river, and so now the river is less polluted than before.

The two pressure points for these arguments are always the same: 1. Alternate Explanations for the curious fact 2. the plausibility of the author's explanation

On Flaw, we're primarily concerned with the #1. They want us to see that the author is overconfidently jumping to one possible causal explanation while failing to consider that there could be other explanations.

What could be an alternate explanation for why the Lalolah River went from being the most polluted to the 3rd most polluted?

Maybe that river didn't get any cleaner, but the two rivers that are now ranked higher than Lalolah got worse.

It's possible for Elon Musk to go from being the richest person in the world to the 3rd richest without him losing any money. It could be explained by people who previously had less money than him gaining enough money to surpass him.

Goal

Let's look for something like,

11.

The reasoning in the argument is flawed because the argument

  1. interprets lack of evidence for

    Not Unproven vs. Proven False

    This answer refers to one of the 10 Famous Flaws, Unproven vs. Proven False, in which an author treats a failure to prove X true as evidence that X must be false. This argument has no rebuttal qualities (as Unproven vs. Proven False normally would). The author's evidence never calls out a certain claim that lacks evidence.

    2% picked this

  2. relies on an ambiguity in

    Not Equivocation

    This answer alludes to one of the 10 Famous Flaws, Equivocation, in which an author uses the same term or concept in two very different ways. (This answer is almost always wrong.) The way the author used "most polluted" was clear and consistent: it means "more polluted than any other river in the District".

    1% picked this

  3. does not disclose the basis

    Never a Flaw

    Answers that ask us for specific numbers/measurements or definitions are basically always wrong. The specific details behind the premises aren't what's being tested when we're being asked about the problem with reasoning. We're supposed to grant the truth of the premises and think about how they still fail to prove the conclusion. So we'll accept that Lalolah was ranked 1st and is now ranked 3rd. We aren't supposed to object by saying, "Why should I believe those premises? What was the basis for these rankings?" We're supposed to think, "GIVEN THAT ... it went from being ranked 1st to being ranked 3rd, HOW CAN I FIGHT THE CONCLUSION?"

    3% picked this

  4. confuses the state of the

    Not Part vs. Whole

    This answer refers to one of the 10 Famous Flaws, Part vs. Whole, in which the author assumes that a trait/property that applies to each part of a whole also applies to the whole itself (or vice versa). This argument didn't do that. That would have felt like, "Each river in the district is polluted. Thus, the district as a whole is polluted."

    2% picked this

  5. Correct

    equates a decrease relative to

    Why this is right

    For all Flaw answer choices, we can ask ourselves: 1. Did this really happen? Is it descriptively true? 2. Does it matter? Does it point to some problem with the logic? It's certainly true that the author goes from Evidence about a relative decrease (the Lalolah River went from being more polluted than all other rivers, to being less polluted than two rivers) to a Conclusion that assumes an absolute decrease (she thinks that cleanup measures led to the river having less pollution than it had before). This answer points to a problem with the logic (very indirectly) by suggesting the Alternate Explanation for the curious fact: No, author, the river didn't get less polluted, it's just that two other rivers got so much worse that they surpassed Lalolah in the pollution rankings. If we had read the argument, "Last year Elon Musk was the richest person in the world. This year, he is the 3rd richest. So apparently his decision to buy Twitter has caused him to lose a bunch of money", then this answer choice would apply just the same. We would be able to object, "Wait a sec --- maybe he didn't lose any money over the past year and the real reason that he's now 3rd is simply because two people who used to be under him in terms of wealth have gained enough wealth to surpass him. Just because his wealth changed in relative terms (in terms of how he compares to other) doesn't mean that his wealth changed in absolute terms (it doesn't mean that he now has less money).

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

    91% picked this

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