#11 - If the forest continues to disappear at its present

[harvoolio]

I have two questions (after reading this thread and listening to Jon discuss the question in the Advanced Logical Reasoning course):

1. Are you sure that "all that is needed" introduces a bi-conditional as does "if and only if"? Jon did not diagram this as bi-conditional and I tried verifying this online by looking up truth tables but was unable to do so. Logically, in this example, do we know that by the politician saying "So all that is needed to save the koala is to stop forestation." that if the koala is saved it would have been necessary to stop deforestation."? So all that is needed to save the koala is to stop forestation." rules out saving the koala say by creating a giant sanctuary or bringing them into zoos or any other possible way besides stopping forestation?

2. Is the only thing that can be inconsistent with a conditional statement the situation in which the sufficient condition is true and the necessary condition false (of either the main or contrapositive conditional statement)?

Thank you.

[Daniel Stern]

Whereas the biologist sets up a traditional necessary/ sufficient statement -- if deforestation continues, the koala will become extinct -- the politician does a mistaken negation of that and assumes that if deforestation stops, the koala will be saved.

The politician's statement can indeed properly be diagrammed as a bi-conditional. The politician mistakes the koala's survival and the cessation of deforestation as both necessary and sufficient for one another.

I hope this is helpful.

Dan

[bella243]

What is this question called? Must be true?

[Adam Tyson]

We classified it as a Must Be True, Bella, but it's also kind of a hybrid question in that we are looking for something that is consistent with one statement (that's a Must Be True idea) and is, at the same time, inconsistent with another statement (that is a Cannot Be True idea). So it's actually both a Must Be True and a Cannot Be True at the same time! This question was from October 1991, and we haven't seen too many like it since. Weird and fun!

When I first read the stimulus I expected a Flaw in the Reasoning question, because the politician definitely misunderstood the claim made by the biologist and turned an ordinary conditional claim into a biconditional. I was a little surprised at the stem, but once you know what the politician did wrong it's not a big step to finding something that shows that error.

[clairewhited]

I am a little confused about the differentiation between slowing deforestation and stopping. I understand the biologist to be claiming that deforestation couldn't continue at the same rate but the politician to say that the only way to save the koala was to stop deforestation. I selected D because I thought it showed another possibility for saving the koala without "stopping" deforestation (ie. slowing it) which would be inconsistent with the politician's statement but could be consistent with the biologist's (the koala did not approach extinction and the forest did not continue to disappear at the present pace). Is there a different way I should be approaching this question or the wording?

Thank you in advance!

[Robert Carroll]

Claire,

The politician's statement shouldn't be read as claiming that something more extreme is necessary to stop the extinction of koalas. The politician is saying "all that is needed" is to stop deforestation. The contrapositive of the biologist's statement is something like:

koala survives deforestation slowed

The politician isn't saying that more is necessary, but instead erroneously inferring the Mistaken Reversal of what the biologist said:

deforestation slowed koala survives

Now, it's true that the politician switches how extreme the language is, talking about stopping deforestation rather than merely slowing the rate of it. But the point of the politician's statement isn't to say that we need to do more. The politician is saying that all we need to do is stop deforestation - that nothing else is necessary, so that stopping deforestation is sufficient to save the koala.

Robert Carroll

[ogbrandojay]

@steve, isn't the claim that something is needed mean it's necessary, not sufficient. In that case the logic would be
saveK --> (needs) ~Deforestation.

from there we could say that the correct answer choice, AC B, is correct since:
~deforestation --> ~saveK

this is consistent with claims for the bio, but a mess for the politician.

[Jeff Wren]

Hi ogbrandojay,

The politician's statement can be tricky to diagram, and this question gives many people trouble.

The politician states "All that is needed to save the koala is to stop deforestation."

While you're right that the words "is needed" on their own would convey the idea of necessity but here they are being used in the context of the word "all" which conveys the ideas of sufficiency. In this context, the word "all" dominates in terms of the meaning.

For example, if I said "All that is needed to pass this test is to study for 1 hour" that would mean that studying for 1 hour would be sufficient to guarantee that you would pass (according to the original statement).

On the other hand, if I said "If you want to pass this test, you will need to study for at least an hour" the studying would be necessary but not sufficient to guarantee that you will pass.

So here, the diagram for the politician would be:

SD (for Stop Deforestation) -> SK (for Save Koala)

Now the one thing that cannot happen according to this conditional statement is the sufficient occurring without the necessary, which would be that we Stop Deforestation, but we don't Save the Koala. This is exactly what happens in Answer B. Notice that Answer B is not a conditional statement. It is simply stating that the Deforestation stopped and the Koala went extinct. In other words, it's showing the sufficient condition happening without the necessary, which directly contradicts the politician's claim.