[Guest]

1) All ravens are black

This can be translated to

2) Everything that is not black is not a raven

the first "fact" is supported by:

3)Nevermore,my pet raven is black

And the second one by:

4) This green (and therefore not black) thing is an apple (and not a raven)

However does all of that prove all black things are ravens in any way?

[Guest]

No it does not, it only states the ONLY black things CAN be Ravens, but for instance a black cat won't contradict any of the above...