Please help me to understand, maybe I'm over thinking this, but I'm afraid I missed something......
I feel as if I worked through this as advised but, I don't understand why some of the answer cards have a positive and contrapositive listed in what I would consider opposite of one another. (I worked this one out and concluded that it would be the positive, but the answer card lists it as a contrapositive or visa versa). The flash card has the third premise on this missing premise question written as the answer being:
# 3 P: Z--->D
(~D--->~Z)
My working through the problem comes out this way:
#1P: C--->E * *
(~E--->~C) ~Z ~E
* *
#2P: E--->Z ~D ~C
(~Z--->~E) |------------------------>|
#3P: ?
Solved to be ~D--->~Z (Opposite of the answer or what I listed above)
(Z--->D)
#1C: ~D--->~C
(C--->D)
Can you help me fine tune?
I understand I used the contrapositive of premise 1 to get from ~E--->~C
Then, I used the contrapositive of premise 2 to get from ~Z--->~E because of this, I was able to recognize the missing premise is then, ~D--->~Z.
What confuses me is why the answer card lists ~D--->~Z as the contrapositive of Z--->D and not the positive answer to premise 3, when the known conclusion is known ~D--->~C / (C--->D).
Thank you for your assistance.
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I can see there are some significant formatting issues between the message box my question was written into to here where it changed and displayed my diagrams to nothing like I wrote it out. I tried diagramming when I originally wrote this question using the technique Rob Smoot taught in Missing Premise Office Hours i.e. Getting from ~D ~C, placing ~E and ~Z up above showing me the path to the missing premise ~D--->~Z.
TateDecember 3, 2022
I re-watched Rob's office hours and I saw that he actually covered the same problem. I re-listened to his explanation for this flashcard problem and then another problem where the same thing occurred to him and I am comfortable knowing, whichever way it is written, it's means the same thing.
