Logical Reasoning

PT144 · S4 · Q18 For several centuries there have been

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For several centuries there have been hairless dogs in western Mexico and in coastal Peru.

Conclusion

The dogs must have been transported from one region to the other by boat (probably during a trading expedition).

Evidence (since)

The dogs have never existed in the wild. It would be very unlikely that a rare trait like hairlessness arose two separate times. The vast mountainous jungle separating western Mexico and coastal Peru would have made overland trouble extremely difficult.

Evaluate

The author's conclusion is offering an explanation for a curious fact.

Curious Fact ... how is it that for several centuries there have been hairless dogs in western Mexico and coastal Peru?

Author's Explanation .... the dogs must have been transported from one region to the other by boat.

Whenever we see this type of argument we consider 2 things: 1. can we think of any Alternate Explanation for the curious fact? 2. how plausible is the Author's Explanation?

The author already ruled out a couple possible alternate explanations: - the dogs just roam the wild and ended up in both locales - the trait of hairlessness just spontaneously arose in two different places - the dogs didn't travel overland from one place to another

The author doesn't fully rule them out, but makes the 2nd and 3rd ideas there seem very sketchy / unlikely.

Are there any alternate explanations that would get the dogs from one place to another that don't involve boat or overland?

We can't say by plane, because they have been in both spots for several centuries, so it predates airplane technology.

Maybe a hurricane lifted one off the ground in one place and deposited it in the other? Maybe one of them floated on a piece of driftwood (not an actual boat) from one place to the other?

How about the plausibility of the author's story? What needs to be true for the boat hypothesis to be plausible? Well we have to assume that one of these dogs would be willing to get on a boat / would be able to survive the journey.

Goal

Look for an answer that rules out an alternate explanation for how the dogs ended up in both places or that establishes something required for the author's explanation to be plausible.

18.

Which one of the following is an assumption that the argument requires?

Hairless dogs have never been
Too Strong
Too Strong: never Only Thing Mentioned ≠ Only Thing The author doesn't need to commit to some very extreme idea that the only place a hairless dog has ever been found are these two places. If there was one found in New Jersey last week, it wouldn't mess up her argument in the slightest. Just because she only mentioned those two places doesn't mean she's assuming those are the only two places where they were ever found.
23% picked this
Most of the trade goods
Too Specific: most
The part about "probably during trading expeditions" isn't any of our concern, since the author hasn't actually committed to that idea at all. Furthermore, even if the author were saying "the dogs must have been transported by boat during a trading expedition", we wouldn't care whether boats accounted for 10%, 49%, 51%, 100% of the trade goods that came into western Mexico. As long as there was ever a boat that came from one place to the other, the author's on solid ground. "Most" is wrong 99.9% of the time we see it on Necessary Assumption, because the argument almost never hinges on whether something is true at least 51% of the time or at most 49% of the time.
5% picked this
Centuries ago, no one would
Too Strong
Too Strong: no one except for X The part about "probably during trading expeditions" isn't any of our concern, since the author hasn't actually committed to that idea. Furthermore, even if the author were saying "the dogs must have been transported by boat during a trading expedition", we wouldn't care whether boats also traveled that route for other reasons too. As long as some boats sometimes traveled that route on a trading expedition, the author's hypothesis could still be true.
8% picked this
If hairless dogs were at
Out of Scope: trading dogs
The part about "probably during trading expeditions" isn't any of our concern, since the author hasn't actually committed to that idea at all. The author's argument is just about "the dogs must have been transported by boat". It doesn't matter to the author whether it was actually part of a trading expedition, whether the dogs enjoyed being part of a trading expedition, whether they were sold for a bucket of rice once they got to the other country. None of those are essential details, so the author doesn't need to assume anything about any of them. She's only committing to the idea that they traveled by some sort of boat.
5% picked this
Correct
Centuries ago, it was easier
Why this is right
In order for the author's hypothesis to be plausible, it needs to be more plausible than an option he already ruled out for being implausible. If we say, "Kevin wasn't strong enough to do it. I guess we'll need Marcus to do it", then we're assuming that "Marcus is stronger than Kevin", otherwise that suggestion is nonsensical. Similarly, the author is ruling out the possibility that the dogs could have traveled overland, because it would have been extremely difficult centuries ago. If we negate this answer, it's saying, centuries ago, it was at least as hard to travel by boat between those two countries as it was to travel by overland route. This question ends up testing both Curious Fact / Explanation concepts (this answer states something that would need to be true for the author's explanation to be plausible), as well as Assuming a Difference concepts (the author rules out X for a certain reason and then goes with Y instead, which means that the author is assuming that the certain reason that disqualified X doesn't also apply to Y).
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
57% picked this

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