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liwenong28 August 6, 2020

A or C

Hi so I actually picked A but I note the correct answer is C. Can I clarify that in either/or questions whichever variable we pick, we negate the sufficient condition and not the necessary condition? Thanks in advance!

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shunhe August 6, 2020

Hi @liwenong28,

Thanks for the question! Yup, that’s how you can think of it. When we have a statement like A v B, we can diagram it as ~A —> B.

If you translate the conditional into an everyday “if then” statement, this also makes sense. Say someone says that they’re going to get cream or sugar in their tea. Well, that means that if they didn’t get cream, they got sugar! And vice versa, if they didn’t get sugar, then they had to have gotten cream. They have to get one or the other, since that’s what “either/or” means. And it doesn’t matter which variable you pick because

~A —> B
~B —> A

Are just contrapositives of each other, so they’re logically equivalent. So it doesn’t matter which variable you put in which place, but you have to negate the sufficient and keep the necessary the same.

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