Proof that Every Truth Is Necessary

Over at Thoughts Arguments Rants there's an interesting proof for the notion that every truth is necessary. The simplicity of the proof which assumes a controversial set of modal logic called S5 made me say, "Ooh, neat."

Note: S5 is controversial because it can be used to make a simple and logically rigorous proof of God's existence, which I provide below for fun:

1. g --> N(g)
2. N(g) v ~N(g)
3. ~N(g) --> N(~N(g))
4. N(g) v N(~N(g))
5. N(~N(g)) --> N(~g)
6. N(g) v N(~g)
7. ~N(~g)
8. N(g)
9. N(g) --> g
Therefore, g.