39 LR One Question 11
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MGD,
39 LR One Question 11.
1. Why can't we use the contrapositive to prove a gift is generous?
2. The two statements that result from applying UNLESS indicate this is possible.
3. Can you show the step by step diagram for this question?
Thanks.
RBanks

1. Because we can only read conditional symbols correctly from left to right, so we can only prove what's on the right. And the contrapositive doesn't put generosity on the right hand side. In other words, for the same reason that the (true) statement that NBA players are all men [NBA → Man, contrapositive: Not Man → Not NBA] would allow you to prove someone is a man—if you know he plays in the NBA—but would never allow you to prove someone is in the NBA.
2. Yes, sure, it's definitely possible that some gift is generous. But we're only concerned here with what we know must be true.
3. We'll apply the same exact process from the videos on unless here and if...then here:
First rule:
Not Generous
IBR + WM
→ Not Generous
→ IBR + WM
Not IBR or Not WM → Not Generous
Generous → IBR + WM
Second rule:
GBG or LV → Selfish
Not Selfish → Not GBG + Not LV