What does possibly necessary mean in modal logic [crazy question actually]

[klqc_]

Suppose the following

X is not necessarily not Y.
If X is Y then X necessarily cannot be Z.
Does that mean X cannot be Z?

I probably screwed up stating that...

To clarify
The first line is meant to be a solipsistic statement - I may be all there is.
The second line is meant to state that if I am all there is then I cannot imagine being annihilated.
In the third line I conclude that I cannot imagine my annihilation.


I'm not concluding that we must "live" forever in oblivion but it's kinda the idea.

 

[micromass]

This post does not meet the guidelines of the philosophy forum. Please read both sets of guidelines on the top of the forum.