For U=R lovers

[Serapy]

The S=G thing is actually a fairly well known theory, as it is part of the infamous R=U theory.

I will admit that the actually S=G theory has a bit more credibility than the R=U theory in my opinion, so I do slightly believe in it as a possibility, but in order to fully believe it I need to believe the R=U theory, which I don't believe at all.

Perhaps I'm just talking out of my ass here (but that's what these threads are all about anyway!), but doesn't scanning Griever reveal that he was created from Squall's own mind by Ultimecia?

Yes it does.

So really, there isn't so much an S=G theory, as there is a direct line from the game stating it to be fact?

Saying Griever was created from Squall's mind does not mean that Squall is Griever. In fact, it pretty much blows that theory away. An idea and the individual who has the idea are too very different things.
Griever was a personification of an aspect of Squall's psyche. A collection of thoughts and images given form, nothing more.

The theory still stands. There's nothing in the game that states that Ultimecia possessed Squall, read his mind and created Griever out of it or that she can possess humans and thier minds (yes, there are a few cases, but such cases cannot be proved or disproved.)
However, the game has explicitly stated and displayed that Ultimecia can possess and read sorceresses' minds.

Therefore, the most logical assumption would be ...

Squall told Rinoa about Griever -> Rinoa learnt Griever out of Squall's mind -> more explanations from Squall -> Rinoa fully acknowledged the meaning of Griever -> Later into the game, Ultimecia possessed Rinoa -> Ultimecia fully acknowledged Griever.

She then created it in the final battle from that formation.