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I think I understand now, but what has left me scratching my nose (metaphorically):
Why is it called “B if and only if A”, if what it really means is “B only if A and vice versa”? (Am I correct in thinking that’s what it means?)
I just don’t understand how that translates grammatically. To me, “B if and only if A” sounds the same as “B only if A”. I can accept that they mean different things in the context of logic, just like I can assign any meaning to any label, like I could say that “dog” now means “kite” in a certain context. But it seems unintuitive and doesn’t really make sense to me. Does that make sense?
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“If A then B” means if A is true, then B is guaranteed to be true. Note that if B is true and A is false, “if A then B” is still true.
“B only if A” means the only way for B to be true is for A to be true. It’s weird, but it has the inverse truth table as “(not A) and B”.