Re-posting in this forum in addition to the discussion on the explanation video - I'm having a hard time with A. Doesn't the contrapositive of A also link the ought & promise?
Answer (A) posits that failing to do something one ought to do = failing to keep one's promise.
This is not true and reverses the truth. Promises are a particular instance of something one ought to do. But there are many other things one ought to do that are not promises - e.g., help someone drowning... Accordingly, the reverse of (A) might be true: failing to keep one's promise = failing to do what one ought to do. (This argument presumes that one ought to keep one's promise.)
thanks, that was immensely helpful. It's frustrating that I failed to see that real life application because I was seeing this only in terms of lawgic: ~o --> ~p and I was so sure that the contrapositive was supposed to help bridge P & O ughhh
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Answer (A) posits that failing to do something one ought to do = failing to keep one's promise.
This is not true and reverses the truth. Promises are a particular instance of something one ought to do. But there are many other things one ought to do that are not promises - e.g., help someone drowning... Accordingly, the reverse of (A) might be true: failing to keep one's promise = failing to do what one ought to do. (This argument presumes that one ought to keep one's promise.)
thanks again @LSATisland