"If the forest continues to disappear at its present pace, the koala will approach extinction," said the biologist. "...

vrod11 December 18, 2020

Consistent with biologists claim but not politicians

I’m confused how B is consistent with the biologists claim. In the video it was said you must show sufficient but not necessary. I’m confused about what that means. I don’t understand how this answer is correct or how to solve questions like this in the future.

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shunhe December 21, 2020

Hi @vrod11,

Thanks for the question! So the sufficient and necessary modules will definitely help with a question like this. But basically, (B) is consistent with the biologist’s claim, which is that if the forest continues to disappear at its present pace, then the koala will approach extinction. We can diagram this:

Forests disappear (deforestation is not stopped) —> Save koala

Now, the claim in (B) is that deforestation is stopped, and the koala becomes extinct. Now remember, when we have

A —> B

We CANNOT conclude

~A —> ~B

That’s a mistaken negation. That’s like saying, if you come over, I’ll make you dinner. But that doesn’t mean if you don’t come over, I won’t make you dinner. I could still make you dinner and bring it over to wherever you are. We can’t conclude that. And so

A —> B

and

~A —> ~B

Are both perfectly consistent with each other. And that’s exactly what’s happening here. Just because the koala goes extinct anyway when deforestation is stopped doesn’t mean that it wouldn’t have approached extinction also if deforestation continued. Consistent claims, and so (B) is the correct answer.

Hope this helps! Feel free to ask any other questions that you might have.

Garrett April 21, 2021

I have a question about the sentence, "So all that is needed to save the koala is to stop deforestation,"

I thought "all" introduced sufficient and then the rest of the statement was necessary, but in the video explanation it looks like all introduces necessary. I know I am misunderstanding this statement but I'm not sure how. Please help!

Corinthia-Hicks April 27, 2021

Same question as Garrett; my question is about the set up. I also thought all introduced sufficient; because of this my set up looked like this.

FD@pres pace --> KWextin
contrapositive (not) Kwextin --> (not) FD@pres pace

Corinthia-Hicks April 27, 2021

and for the politician SK--> defor contrapositive (not) defor--> (not) SK
(my questions got split up)