Q18 - For several centuries

[atzhang6v6]

Is A wrong because never found and not exist are different things? if it said did not exist, would it be correct?

[ManhattanPrepLSAT1]

Is A wrong because never found and not exist are different things? if it said did not exist, would it be correct?

Not exactly, that's not the issue with answer choice (A). It should have ruled out the hairless dogs being transported from some other third region to either coastal Peru or western Mexico. Ruling out the existence of hairless dogs in other regions isn't necessary, it's too strong.

This argument concludes that hairless dogs must have been transported by boat between coastal Peru and western Mexico. Why? Hairless dogs have never existed in the wild and the overland route would have been very difficult centuries ago.

First, on the surface, it's not a terrible argument. I'd believe it. But it's not fool proof. What if the dogs reached Peru or Mexico from some third place? But the right answer doesn't go that way. Instead it's a comparison. The argument compares the overland route with the route by boat. After asserting the difficulty with the overland route it concludes that the boat route was more likely. But we don't know anything about the boat route. What if it's even more difficult than the land route? This argument assumes answer choice (E).

Incorrect Answers
(A) is too strong. The argument assumes that hairless dogs haven't been transported to coastal Peru or western Mexico from some third region. But it doesn't assume that hairless dogs have never existed anywhere else.
(B) helps the argument, but isn't assumed. Even if it weren't true, the argument holds.
(C) undermines the argument.
(D) is too specific. We don't need to assume what those dogs would have be traded for.

Takeaway: The LSAT loves to test your understanding of Relative vs. Absolute claims. The claim about the difficulty of the overland route is absolute: that route is extremely difficult. But that doesn't imply anything about the route's difficulty relative to other possible routes.

#officialexplanation

[851869412]

I see Q18 as a absolute vs. relative question. An extremely difficult way might still be the easiest way, compared with other alternatives. If this were the truth, the argument is unfounded. So a necessary assumption is there is no such possibility .

Also, (A) misses the "centuries ago", while (B) does not say "from Peru". So they are not the assumption.

Since I am preparing for the December LSAT, any comment is welcomed.

[bsd987]

Is A wrong because never found and not exist are different things? if it said did not exist, would it be correct?

Not exactly, that's not the issue with answer choice (A). It should have ruled out the hairless dogs being transported from some other third region to either coastal Peru or western Mexico. Ruling out the existence of hairless dogs in other regions isn't necessary, it's too strong.

I don't agree. We are concluding that dogs must have been transported by boat in one direction or another between Mexico and Peru. Our only evidence is the difficulty of land travel and that it is highly unlikely that two different dogs would evolve without hair. This is very flimsy evidence to use to make such a broad conclusion. The assumption, broadly speaking, is that our very narrow evidence is sufficient to conclude with certainty that the dogs were transported by boat in one direction or the other. If there were hairless dogs in other locations at that time, we would no longer be able to conclude from our evidence that the dogs *must* have been transported by boat between Mexico and Peru.

Thus while your assumption is necessary, so would be the assumption that the dogs did not exist in other places several centuries ago. Otherwise, our evidence would no longer prove our conclusion and our argument would be weakened. Therefore, the problem with A is that it says 'have never been found', which is too broad. We only need to know they weren't in other places at the time.

[reginaphalange]

Is A wrong because never found and not exist are different things? if it said did not exist, would it be correct?

(A) is too strong. The argument assumes that hairless dogs haven't been transported to coastal Peru or western Mexico from some third region. But it doesn't assume that hairless dogs have never existed anywhere else.

The argument DOES assume that hairless dogs have never existed anywhere else. First, it has to rule out any place that might have connected Peru and Mexico. Second, it has to rule out any other place as well, because it works on the assumption that hairlessness could not have emerged separately.
The problem with (A) is that it's not dated - we're talking about how hairlessness could have spread centuries ago, whereas (A) just says generally, hairless dogs aren't found anywhere else. Of course they could be found elsewhere NOW - like in Hollywood, for example.

[syp]

I understand why E is correct. However, can you please elaborate why C is wrong? How does it undermine the argument? Thanks.

[ohthatpatrick]

Hmmm, I certainly wouldn't have eliminated (C) based on it undermining.

Since this is Necessary Assumption, my most common reason for eliminating an answer is simply that it is too strong or too specific to be required.

As soon as I see (C) say, "The author must assume that not a single person ever would have gone by boat from Peru to Mexico unless it was for a trading expedition", I know it's WAY too strong.

If we negate this, we're saying, "at least once, someone went from Peru to Mexico by boat for purposes OTHER than trade".

Would that negation badly weaken the argument?

Of course not, and thus it can't be a correct Necessary Assumption answer. Note that the author is primarily concluding that dogs were transported by boat, and he only throws in that "PROBABLY during trading expeditions" as an unimportant aside, speculating what the nature of the boat trip may have been.

I think the original poster saying that (C) undermines was thinking to himself, "This author is speculating that hairless dogs ended up in both places because the dogs were on a boat going between Peru and Mexico. (C) makes it seem like people would ONLY go by boat between Peru and Mexico for one specific reason, so (C) somewhat limits how frequently boats would have gone between the two areas. The less likely those boat trips were to happen, the fewer chances there are for the author's dog-on-the-boat hypothesis to have occurred."

That's a bit of a stretch.

[LukeM22]

I get why E is right, but, I still don't see why A is wrong.

The argument is clearly assuming that hairless dogs must have originated from one of these two locations-- if not, the last sentence is completely irrelevant-- there is no need to conjecture how transportation could have occurred between the two cities if we have not even established that there needed to be transportation in the first place. The argument hasn't stated much less established that hairless dogs have not been in existence in pretty much every other South American/Latin American region... I feel that A pokes at this, and if we apply the Negation Test to A, it pulls the rug from under the argument... there is no need for boat travel if the hairless dogs have been in existence in Central Mexico (or somewhere really easy to get from Western Mexico).

[ohthatpatrick]

It's just too extreme or too vague depending on how you wanna slice it. You're definitely right in the gist of your thinking.

We could make (A) correct by saying
(A) Hairless dogs have not been commonly found in any regions between western Mexico and coastal Peru

Negating THAT is a powerful objection.

Negating (A) just means, "at least one time, a hairless dog was found somewhere besides western Mexico and coastal Peru."

That's not enough specificity to worry the author. He can just as easily believe that dog was found in slightly-inland Peru as you can believe that dog was found in between Mexico and Peru.

Meanwhile, negating (E) is saying, "boat travel was at least as difficult as overland travel".

That makes the author's pivot from "overland is hard, so it must be boat" seem moronic.
Negating (A) is way less powerful of an objection, and the extreme wording of "never" and "anywhere" is why the negation is such a weak idea.

Hope this helps.