2. He's Awake (And Always Has Been)
This is the simplest theory of the lot. What the film explicitly presents as reality is reality, the flashes of Mal and the kids in the real world just fractures of Cobbs mental state. Its the ultimate happy ending; Cobb succeeds in Inception, gets let back in to America and reunited with his kids. This makes sense on a basic level; if we cant trust the films presentation, then all these theories can be argued away. Theres plenty of basic evidence on this case; the older actors for the kids and the presence of Michael Caine (who never appears in a dream and believes as such) to name two. But the meat of theory relies on totems. If you take the spinning top as Cobbs totem, then youre getting into the conjecture that most people discussing the film settle on. The early title card makes it impossible to tell the whether to top will fall or spin forever, but theres enough of a wobble to be able to be able to argue it could fall. But, continuing the point made before about the top being Mals, this leaves it useless and a chance for us to focus on Cobbs real totem; his wedding ring. Throughout the film, Cobbs wedding ring obeys a rule. Namely, he only wears wedding ring in a dream (when he's still obsessed with Mal), not having it on when he's awake (and without her). And in the ending sequence he is very clearly not wearing it. From what is presented in the film, this is the theory that I think has the most weight, using totems which are stronger evidence than some of the others conjecture. But the fact that the ending is so open for discussion leads to an interesting, all encompassing theory...