P: A–some–CP: ?C: not Z–some–A

gharibiannick March 17, 2020

Confusion

So Im not understanding how the expert did it but I got the correct answer differently AsomeC ? NotZsomeA AsomeC ? AsomeNotZ So now I need to connect C to Z... AsomeC -> AsomeNotZ AsomeC-notZ The missing premise is: C-notZ or Z-notC Is this the right setup and approach or was this just coincidental ?! Thank you

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BenMingov March 17, 2020

Hi Gharibiannik, thanks for the question.

I am looking at your method and it seems good to go!

The only thing I'd like to note is that the one condition you have up there:

AsomeC -> AsomeNotZ

This is not how we would connect it. This condition would mean "if some As are Cs, then some As are not Zs" which is a completely new condition.

I would for future reference just note it the way you were speaking it through earlier. We need to connect C to Z.

That would result in:

A some C - > Not Z

This would produce the conclusion that we have. A some Not Z (Not Z some A)

gharibiannick March 17, 2020

oh okay, I guess I was doubting myself.

as for the AsomeC -> AsomeNotZ, what I meant was I have to get from AsomeC to AsomeNotZ. I did not attempt to make a new condition. That may have been an error on my part.
Thank you for the feedback though.

Ravi March 17, 2020

@gharibiannick, let us know if you have any other questions!

Raechel-Brodsky May 23, 2020

Hi there! I also got the answer right but when looking at the contrapositive of the explanation I am confused on how
not Z-some- A turns into not A-some- not Z?
Why does the explanation of he contrapositive in the conclusion negate the A and thus not change the Z? I thought the contrapositive of "Not Z-some-A" would look like "A-some-not Z" when working with some and must quantifiers.

Skylar May 29, 2020

@Raechel-Brodsky, happy to help!

With S->N statements, we reverse and negate to find the contrapositive. With quantifier statements, we can only reverse to get a new some statement.

So, if we have the statement: not Z - some - A
We can only deduce to find: A - some - not Z

I am not sure where you're seeing the incorrect deduction that you reference, but your logic appears to be correct.

Does that make sense? Please let us know if you have any other questions!