There is an important clue in the final scene that is easy to miss, and
David Kyle Johnson, author of Inception and Philosophy: Because
It’s Never Just a Dream, believes that Christopher Nolan
intentionally misdirects the audience’s attention in the final scene.
In short, Johnson’s view is the whole movie is a dream, Saito’s in particular.
Johnson gave a Google tech talk on the subject, and his slides
are also available. The film is deep and rich. Johnson and his collaborators likewise sank considerable time and thought into their analysis of Inception and its implications. My summary of Johnson’s justification for his position is below.
To start, subconscious elements work their way through dreams, e.g., the train barreling down the street in the rain dream, the random string of numbers in the hostage scene appears repeatedly in later scenes: the safe combination, the fake phone number, hotel room numbers. At the beginning of the film, Saito dreams of a mansion on an ocean.
Picking up on a big clue in the final scene may require turning on the closed-caption subtitles. Cobb asks his children what they’ve been doing, and they reply that they were building a house on a cliff.
Nolan leaves many clues that the film is a dream.
- Mombasa was like a maze.
- The walls close in around Cobb.
- Agents appear out of nowhere.
- Saito appears out of nowhere to rescue Cobb with a cheesy line about protecting his investment.
- Cobb’s father-in-law pleads with him to come back to reality.
- Eames is a dream forger who is able to pickpocket people without touching them.
- Eames bet his last chips in the real world but magically produced two stacks of chips to buy beers.
- Mal somehow got to the other hotel across the street in the suicide scene, but Cobb begged her to come back inside to his room, reasoning that would have “made sense” only in a dream.
- The top totem gives us no information about whether Cobb is dreaming because everyone else knows how it works.
- The Édith Piaf song that signals the end of the dream is 2 minutes 28 seconds long. The film is exactly 2 hours 28 minutes long.
When someone commits suicide in limbo, the subject goes one layer up. For Cobb, the next layer up was the snow fortress. But everyone was gone, so he filled the empty dream space with his own expectations, namely the airplane scene. Eames pickpockets the passport in the airplane without touching Robert, the way he did in other dreams.
This interpretation makes a much better film. Consider:
- All characters except Cobb are flat and one-dimensional — many didn’t even have last names.
- Editing in the real world jumps around without transitions.
- Saito swoops in out of nowhere with a cheesy line about “protect[ing] my investment.”
If the entire film is a dream, these gaffes become strengths. The characters are flat because they’re projections, not because the writing is bad. The jumping around is not bad editing but because that’s how dreams run. Saito’s cheesy line becomes a subtle clue that Cobb is dreaming.
The answer above repurposes content from an answer of mine on scifi.SE.