Q12 - Australian marsupials and placentals

[ali.charania]

I had a difficult time with this question. Could someone please help me by breaking down the answer choices? Thanks!

[timmydoeslsat]

We are given a sufficient assumption question stem. Our task is to prove the conclusion true.

Our main conclusion that we are trying to prove is that placentals in Australia are not native to Australia.

The other stuff prior to that is background information where we are told of over 100 species that are called placentals.

And what was the reasoning that these placentals are not native? We know that these placentals had ancestors that could come from long distances. (And do not worry about the dingo, it is just an exception in this case and it is not making or breaking our argument)

So, we can clearly see that this fact does not prove that the placentals are not native. So what if the ancestors could do all of those great feats? Can't they still be from Australia?

So we can expect a sufficient assumption that makes this fact matter. And this is what answer choice (C) does. It gives a characteristic of what a native Australian placental must have, which is that it could not have had ancestors that could do those great feats to reach Australia. So we would arrive at the idea that we have species of placentals that are definitely not native, as they do not meet that requirement.

[ohthatpatrick]

Let me add the "structural nerd's" perspective on this one, since Sufficient Assumption is the one question type that can almost always be answered mechanically/mathematically.

The argument core is:
(prem) capable of swimming/flying/floating long distances
-->
(conc) not native to Australia

The correct answer needs to logically connect those two pieces.

(C) is a conditional statement that says
Native to Australia --> incapable of reaching Australia from elsewhere

Like many, if not most, correct answers to Sufficient Assumption questions, this is the contrapositive to the argument's reasoning.

If we contrapose it, (C) says
Capable of reaching Australia from elsewhere --> Not native to Australia.

=== other answers ===

For Sufficient Assumption, the other answers are all wrong because they're not right ... that is, none of them prove the conclusion is true. But it's worth noting that correct answers to Sufficient Assumption questions are almost always of conditional strength (all, no, only, unless, requires, if, then, etc.)

Moderate language that allows for exceptions is almost never sufficient to guarantee that a conclusion is true.

(A) "some" is a red flag, not conditional --- "marsupials" are completely irrelevant; we're trying to prove an argument about "placentals"

(B) "probably" is a red flag, not conditional -- this answer doesn't connect to the premise at all

(D) Marsupial found in Australia --> capable of swimming/flying/floating long distance

(close-ish, except again the conclusion we're trying to prove is about placentals, not marsupials)

(E) "typically" is red flag, not conditional -- also again an irrelevant answer about marsupials instead of about placentals.

Hope this helps.

[WaltGrace1983]

I know (D) is wrong but could it possibly be the type of answer choice that would strengthen the argument? I know that there is still a long way to go but could it be that, because these marsupials couldn't swim long distances and because placentals could, it gives more reason to believe that the placentals aren't native?

I think that (B) could also strengthen the argument as it is much too weak to be an answer that is sufficient. The argument talks about basically "all" - or at least "most" - and the answer choice talks about "many" were "probably" introduced when people settled there.

[christine.defenbaugh]

Interesting question, WaltGrace1983!

Something that merely strengthens the argument would be mighty tempting on a Sufficient Assumption question, as it would go the right direction but fail to completely close the deal. But remember that a strengthener is going to typically make some central assumption of the argument more likely to be true.

The central assumption of this argument is that things that can go the distance (swimming, flying, or floating) couldn't possibly be native to Australia.

can go distance --> not native
native --> can't go distance

(D) can't strengthen the argument, as it doesn't make that idea any more likely. First, we don't actually know that the marsupials discussed are native to Australia (don't bring in outside knowledge!), so (D) could be talking about a bunch of non-native marsupials. If it is, there's no way to even remotely connect this to the argument. What marsupials do or don't do doesn't really tell us anything about placentals.

But let's say (D) was discussing native marsupials, explicitly, that can't go the distance. Does this make it more likely that there is a rule in the universe that native Australian species can't go the distance?

If I am not eating pizza for lunch, does that make it more likely that there is a rule that I can never eat pizza for lunch? I'd argue no - or if it does strengthen, it does so in only the most minimal way. All it really does is provide one instance where you know the assumed rule wasn't broken.

As for (B), you are spot on about the weakness of the terminology here - 'probably' and 'many' can't come close to sufficiency. And this answer certainly seems to make the conclusion a bit more likely - but it doesn't make the central assumption more likely to be true, which is what strengtheners are supposed to do. (B) has absolutely nothing to do with these species ability to go the distance, which is the argument's only support for the conclusion.

Really interesting analysis, but I would say neither of these would be a win for a Strengthen question! And that means that it is not only their lack of strength that makes them incorrect for this Sufficient Assumption question!