If that insect is a bee, it can only sting once. It only did sting once. So it is a bee.Which one of the following ex...

shunhe February 25, 2020

Hi @Bauer22,

Thanks for the question! (D) is a weird answer choice, but the difference is that the “only one more X is needed” construction introduces a sufficient conditional. Thus, we actually diagram (D) as

P1: One more thunderstorm —> Roof ruined

P2: ~Roof ruined

C: ~One more thunderstorm

Which is different from the stimulus reasoning, which is that of a mistaken reversal and fits (A) more.

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

KiaBrodersen November 13, 2023

Can someone explain why the sufficient condition for Answer D was "one more thunderstorm". Using the rules, "only" introduces a necessary condition. Further, saying that one more thunderstorm is "needed" seems also like it would introduce a necessary condition and not a sufficient. So I had diagrammed answer D like this:

P: Roof Ruined --> one more thunderstorm
Contrapositive: Not roof ruined --> not one more thunderstorm.
P: Not roof ruined (roof was fine)
C: No thunderstorm

I took this as they were invoking the necessary condition of the contrapositive to conclude the sufficient of the contrapositive which would be a violation of the don't just reverse. I understand why A is correct, but I'd like to understand why D was diagrammed like that.

KiaBrodersen November 13, 2023

wait sorry I typed that out incorrectly I diagrammed it like this:

P: roof ruined --> one more thunderstorm
Contrapositive: not one more thunderstorm --> not roof ruined
P: not roof ruined (roof was fine)
C: no thunderstorm.

this is what I meant to say my diagram was and my question still stands.

Emil-Kunkin November 13, 2023

D is a great example of why I don't like only relying on keywords. The word only here is serving to diminish something, not to set up and exclusionary situation. We can use the word only in a way that triggers a necessary condition "the only person who can play that bad is Zac Wilson." But, the word only can be used to qualify something as not major, as in "I am only a little hungry." Here the word only is being used in the latter sense. That is, the word only could be substituted for the word even, or for "it would take just one."

We should also take the plain meaning of the sentence in mind. The sentence is clearly not saying that the only thing that could destroy the roof would be one thunderstorm: this runs counter to the sentence and to common logic. If you find a counterintuitive result with a diagram like was the case here, try to rephrase the sentence in a more common sense construction if possible.