Conditional Logic - need help with interpretation

pfjddream

I am confused between the difference of these two forms of conditional logic

not A -> B
not B -> A

versus

A -> not B
B -> not A

Do both forms above really mean either or, but not both?

In one of the games explanations, I remember coming across a point that starting with a negative term as the sufficient condition, meaning where the absence of a sufficient condition guarantees a necessary condition is somehow different than starting with a positive term for the sufficient where the presence of a sufficient condition guarantees the necessary condition. BUT I am having trouble seeing if there is a difference in the meaning of the above two forms and hat kinds of inference I can make from them.

Can someone please clarify this? I am really confused.

Thanks,

Pamela

jdawg113

nope, think of worlds, the top means you can have no A but have B, have no B but have A, or have A & B
the bottom means you have A but not B, B but not A, or Neither A or B

pfjddream

Thanks!

So the first one is either or (possibly both) and the second one is either or but not both