Missing Premise

I am having trouble with the missing premise drills. Any tips on how to answer the missing premise? I am creating all of the contrapositives but it seems that there are certain leaps from premise to premise that are required but not sure how to identify those S&N relationships.

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shunhe January 30, 2021

Hi @WCS,

Thanks for the question! So let’s say you have

P: ~A —> ~B
P: ~B —> C
P: ?
C: ~A -> X

Now we want to get to the conclusion. Well, start off by trying to find the sufficient or necessary conditions in the premises. So we want ~A on the left or X on the right. We see ~A is on the left in the first premise and start with that. Note that you can chain it to the second premise. So we have

~A —> ~B —> C

And we have to end

—> X

So now let’s see if we can connect those, and we can if we just have

C —> X

and so that’s our answer.

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