How To Find the Conclusion on Argument Completion Drills

It it possible to get a walkthrough on the argument completion drills? I cannot seem to get the Conclusion correctly. I always switch around the variables (like if they exist or not). For example how would you do this problem: P: not A - not B P: not B - C P: C- X C: ? I thought it would be not A - X for the conclusion because of the transitive property but it said I was wrong.

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shunhe January 28, 2021

Hi @Brady,

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

P: ~A —> ~B
P: ~B —> C
P: C —> X
C: ?

We want to try to find the conclusion, right? So let’s try to put as many premises together as possible. Note that the first, second, and third premises can all be chained together as follows:
~A —> B —> C —> X

which is just the transitive property. That allows us to conclude??~A —> X

which should be the conclusion. If it said you were wrong, it might have wanted the contrapositive, which is just

~X —> A

And you were actually right, since those statements mean the same thing.

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