#19 - For there to be a thriving population of turtles in a pond,

[Administrator]

Complete Question Explanation

Justify. The correct answer choice is (E).

In this conditional argument, we are told that in order for there to be a thriving population of turtles in a pond, it is necessary that the conditions at that pond be beneficial to turtles. This can be diagrammed as follows:

TPoT CBT

The contrapositive of this statement is as follows:

~CBT ~TPoT

We then are told that the water in Wallakim Pond is acidic. Therefore, there must not be a thriving population of turtles at Wallakim Pond. This can be diagrammed as follows:

A (WP) ~TPoT (WP)

As can be expected in a Justify the Conclusion question, there is a gap in the stimulus. In this instance, it's pretty easy to spot: the acidity of Wallakim Pond renders it incapable of sustaining a thriving population of turtles, without any mention of the beneficial conditions that was said to be necessary earlier in the argument. It looks like, then, that there are two possible prephrases to choose from:

A ~CBT
OR
~CBT A (WP)

Since there are several ways that a pond's conditions might not be beneficial to turtles, it looks like our first prephrase is our best bet. We should look for either that conditional statement or its contrapositive (CBT ~A) as either could be the correct answer.

Answer choice (A): This is a mistaken negation of our prephrase. This answer choice says ~A CBT, but we are looking for A ~CBT.

Answer choice (B): This doesn't account for the beneficial conditions for turtles we saw earlier in the argument, so it's safe to skip this answer.

Answer choice (C): Again, the gap is unaccounted for here, so we can skip this answer choice. Sosachi Pond was merely mentioned as a counterexample to Wallakim Pond and is irrelevant to our conditional statement.

Answer choice (D): This is a mistaken negation of the second conditional statement in our stimulus and is thus incorrect.

Answer choice (E): This is the correct answer choice. This is the contrapositive of our prephrase, which successfully connects the beneficial conditions at a pond to it being not acidic (CBT ~A)

[merkvslsat]

I eliminated B,C,& D immediately. I was stuck between A and E but picked E because this is a SA question, and for SA you pick the powerful answers.

But logically speaking.
Thriving population -> Conditions beneficial
Water acidic -> ~thriving population

E states Conditions beneficial --> ~acidic , whereas A is the inverse, putting not being acidic as the sufficient conditions and conditions being beneficial as necessary which didn't make sense to me.

[Adam Tyson]

You analyzed the question correctly, merkvslsat - nice job! What you called the "inverse" in answer A is what we would call a Mistaken Negation. It does us no good to say that non-acidic water is beneficial when what we need to say is that acidic water is not beneficial!

[supernerd]

Hello!

I still do not understand why the correct answer is not C? with the negation test, C would read "the water conditions at S pond are NOT more beneficial to turtles than are the water conditions at W pond." Is this wrong because since the argument not about the ponds and we know nothing about S pond .. the assumption must be about acidity?

Also, the "only if" in E provides is stronger than "if" in A right? upon first glance, i thought A and E were the same but E is stronger.

Does E read: IF the conditions at a pond are beneficial to turtles (s.a), THEN the water in the pond is not acidic (n.a.) ??

[Adam Tyson]

Looks like you got this all figured out, supernerd! E is better than A because "only if" instead of "if" in that relationship gets the conditional relationship in the correct arrangement rather than mistakenly reversing it. Your rewording of answer E is perfect! And yes, answer C is not good enough to prove the conclusion because one pond being better than the other doesn't prove that the worse pond isn't good enough. We don't much care about comparing the ponds to each other; we need to focus on the pond that is the subject of the conclusion and prove that it is valid.

And that's the key here: "prove." This is not an Assumption question, but a Justify the Conclusion question, wherein we need an answer that proves the conclusion of the argument is valid. We need to KNOW that Wallakim Pond does not have a thriving population of turtles.

Incidentally, if we had been asked an Assumption question, answer C would still not be correct because the author didn't have to assume that Sosachi is better than Wallakim. Maybe, although Sosachi has non-acidic water, it has something else wrong with it that makes it a problem for turtles? Sosachi could be a toxic waste dump and it could still be true that Wallakim has no turtle population due to acidic water.

[Becca1924]

Hi! I'm having a hard time again with sufficient and necessary and I apologize if I'm not able to articulate fully. I'm torn between A, D, and E. I see that "only if" is the strongest, and we want the strongest answer for justify questions, but I thought that indicated a necessary condition, not a sufficient one.

For example, if A (condition) then B (result) is sufficient and B only if A is necessary. The passage's conclusion is the contrapositive of A then B if B is the thriving population of turtles and A is beneficial pond conditions. For our specific answer, though, A = not acidic and B = beneficial pond conditions. Then, answer choice A would be If A B and answer choice E would be B only if A.

I chose D because of the substitution principle and I'm unsure how others eliminated it so easily. If not acidic beneficial and beneficial thriving pop., then couldn't I just cut out the middle man? Maybe I'm thinking about this too much.

[Robert Carroll]

Becca,

Strength of answer is always relevant to Justify questions, but here I think it's muddying the waters. The clearest thing to do with this stimulus is to diagram it, figure out what it's missing, and look for exactly that statement.

So, the first sentence:

thriving turtles beneficial conditions

The second sentence:

acidic(Wallakim)

The conclusion:

thriving turtles(Wallakim)

This doesn't work because we have no idea how acidic water has anything to do with the other premise or with the conclusion. So that seems like a good area to make a connection.

Because the conclusion is the negation of the sufficient condition of the first sentence, it will probably help my understanding of the stimulus to contrapose the first sentence. So:

beneficial conditions thriving turtles

Now I can see what if I can prove that the conditions at a certain place are not beneficial to turtles, I can infer that that place will not have a thriving population of turtles. Well, I want to conclude that Wallakim does not have a thriving population. So I want to prove that Wallakim does not have conditions beneficial to turtles. I don't have that yet, though. I do know one specific fact about Wallakim - it has acidic water. So I should attempt to connect that to beneficial conditions in some way. I want acidic water to make conditions not beneficial to turtles. This conditional does so:

acidic beneficial conditions

Diagramming answer choice (E), we see that "only if" indicates the necessary condition, and the rest of the answer is sufficient. That matches our prephrase perfectly.

Answer choice (D) diagrams like this:

acidic(Wallakim) thriving turtles(Wallakim)

That does no good. Wallakim's water IS acidic. It makes no difference what would have happened if if weren't - we already know that's not true. In fact, that answer is a Mistaken Negation of what we want.

Answer choice (A) has a similar problem:

acidic beneficial conditions

But...Wallakim IS acidic. So, again, what happens if it's not is not helpful.

Further, note you used a Mistaken Reversal of the first sentence when you said:

beneficial thriving

It seems that, even with that in place, your chain of conditionals (again, this involves a Mistaken Reversal anyway) delivers:

acidic thriving turtles

That's a Mistaken Negation. Wallakim IS acidic, so saying what would happen if it were different from what it is is irrelevant.

Going beyond this question specifically, note that every conditional, by definition, has a sufficient condition and a necessary condition. When we talk about conditional indicators, we're talking about which of the TWO (always two) conditions the indicator is tagging. If only one indicator is present, it just means that the other part of the conditional had no indicator - that doesn't mean that condition isn't diagrammed.

Robert Carroll