In each dream there are always a "Dreamer" (the one that creates the dream world, the world collapses if the Dreamer wakes up) and a "Subject" (his/her subconscious creates projections that attack intruders). The Subject is the typical victim of a con, but it's not always that way. In Ariadne's dream, Cobb is the Subject, but there is no con:
Ariadne: Who are the people?
Cobb: Projections of my subconscious.
Cobb: Yes. Remember, you are the dreamer, you build this world. I am the subject, my mind populates it. You can literally talk to my subconscious. That's one of the ways we extract information from the subject.
The other participants (or sleepers) in a shared dream are neither Dreamers nor Subjects - although they can make minor changes to the dream, consciously (Eames transforming himself or conjuring a weapon) or unconsciously (Mal and the train, involuntarily summoned by Cobb), the dream does NOT end if they exit and they are never seen making major changes or conjuring more than one own projection. A participant can also become the Dreamer in another dream layer, in this case he/she has full Dreamer powers in that level. Instead, the Subject is always the same, even in Layer 2/3, or at least this is what is depicted in the movie (Saito at the beginning, Fischer in the main inception con).
The PASIV manual does not mention these roles. It says that all participants must connect their wrists to the machine, then you push the button and the dream begins.
So how do you tell the machine who is the Dreamer and who is the Subject?
(apart of the usual "very well thank you")
Possible theories, but probably incorrect:
- the Subject may be the only one character who does not know he/she's dreaming. First counter-example: Fischer is still the Subject even after Cobb tells him he's dreaming (but they are in Level 2, while Fischer thinks he's in Level 1...). Second counter-example: see the quote above, in the Paris dream, Ariadne is the Dreamer (at the beginning she doesn't know she's dreaming - probably because she's not yet trained in shared dreaming - but when she knows, she defines the dream-Paris, bends streets, creates bridges, etc) and Cobb is the Subject (his projections attack Ariadne) even if Cobbs knows he's sleeping and is an expert in shared dreaming. If Cobb knows from the beginning that he's sleeping and that he's the Subject, this theory is false.
- the Dreamer may be the first one who connects to the PASIV. Counter-example: often they seem to connect to the machine at the same time. For example, on the plane, the flight assistant pushes the button when everyone is already connected to the machine, so everyone receives the chemical at the same time. So this theory is also false.
Other possible theories:
- switchs and controls of the PASIV which are not documented in the manual.
- a mental thing. E.g. before falling asleep, the future Dreamer must concentrate on the "role", maybe repeating in his/her mind "I'm the dreamer, I create the world, I want to enter X's subconscious" (Maybe Ariadne is instructed to do this offscreen, but she's not well trained and/or she doesn't have a totem yet, so she forgets she's the Dreamer, and Cobb must tell her, so she regains her Dreamer powers); the other participants may think "I want to join Y's dream into X's subconscious"; the Subject is the one that does not "prepare" so his subconscious gets invaded (maybe Cobb "leaves his mind open" to let Ariadne do it in Paris). An interesting theory, but I can't find canon to support it.
- This is Nolan, so, according to how you interpret the ending, of course
there are no "roles" and no "cons", Cobb was dreaming all along, Cobb is the only character in the whole movie
Have the filmmakers explained the Dreamer/Subject selection?
Or are we supposed to just accept this as part of the sci-fi setting[*], relax (La-La-La) and follow the plot - a very hard task by itself?
(Edited for clarification: the possible distinction between Dreamer and Architect has nothing to do with my question. My question is only about the factual distinction between Dreamer and Subject - they have clearly different "powers" in the dream, but how do they "receive" these powers?)
[*]: together with the absurdity of a intravenous chemical "connecting" different dreams! a "magical" drug may explain the lucid dreaming, but "magical" wired headbands would have seemed more credible for the "sharing" thing