Explaining Inception: an FAQ Guide

DREAMERS

• Level 1: the one with the van, dreamed by Yusuf, "The Chemist"
• Level 2: the one in the hotel, dreamed by Arthur, "The Point Man"
• Level 3: the one in the snow, dreamed by Fischer, "The Mark"
• Level 4: the one in the crumbling city, dreamed by Cobb, "The Extractor"

OR (alternative explanation of Level 4) Limbo, a level shared by several dreamers.
OR (alternative explanation of Level 3) dreamed by Eames, "The Forger"; populated by Fischer.

DESIGNERS

Levels 1-3 are designed by Ariadne, "The Architect". 
Level 4 is designed by Cobb, The Extractor, likely based on his memory of limbo (which, in turn, was designed by Mal "The Shade" and Cobb, based on their memory of reality).

POPULATION 

Levels 1-3 are populated by Fischer's unconscious (with the occasional intrusion from Cobb's unconsious).
Level 4 is populated by Cobb's unconscious.

OR (alternative explanation of Level 4) Level 4 is unpopulated, except for Cobb's intrusions.

Normally, one would wake up if one dies in dream. However, in the case of the last mission a strong sedative is used which prevents waking upon death. Instead, upon death one enters a state called "limbo", which is usually a state of delirium where the character can no longer tell reality from a dream. If the sedative operates at all levels, this will be the case for all levels. If the sedative only operates on Level 1 - if, for example, it is only administered on the plane, as some have conjectured - then death only leads to limbo on Level 2 (death on all other levels should lead to either a regression to a previous level, or to Level 2).  

Limbo is a state of mind a character experiences, or a final dream space a character visits, if they die in a dream while under heavy sedation, for example during the final mission. Characters in limbo find it difficult to distinguish reality from a dream, they become "lost" in the dream and gradually forget the reality they once knew. If a character dies in limbo without acknowledging the unreality of their situation, they wake up in a vegetative state - as Eames puts it, their brain turns into "scrambled egg". Cobbs and Saito are seen struggling to remember in the final limbo scene.  

Limbo is "pure subconscious" and "unconstructed dream space", shared by any character that falls into it. The only objects present in Limbo are those residual objects left by characters that have been to Limbo before, and are now sharing the dream with you.

There is some debate about whether the "ruined city" scenes are set in Limbo proper, or just a recreation of Limbo from Cobb's memory of his previous (presumably genuine) Limbo experiences. The only sure representation of Limbo in the film seems to be the rocky beach scene that recurs, where Cobb is washed up on the shores of his subconscious. 

The rocky beach scene at the end was a Limbo for Cobb, but he was protected in it because he and his architect chose to go together.  Had he gone alone, he may have not recovered.  Note in the penultimate scene that Cobb and Seito are the only two in Limbo.  And that before Cobb went, his architect asked him if he wanted her to go also.  By then, Cobb had learned enough about discerning the truth and had resolved the guilt he felt regarding his wife's suicide, so the one truth he had been hiding from everybody (save his architect) no longer infiltrated his dreams.  That enabled him to go alone, knowing he would come back. 

 

In general, a kick is anything that would jolt you from a sleeping state to a waking state. We are shown several types of kicks. Cobb is dunked in water from his Level 2 dream in the first dream shown in the movie. The sensation of falling is induced in several of the dream states during the heist.

As demonstrated in the warehouse during training, a kick is used to wake the dreamer from the next level of dreaming, it basically takes you "up" a step. The sedative used to allow for dreams within dreams leaves the inner ear unsedated (the part that detects motion), and so a "kick" - a falling sensation - will be felt by the dreamer in the dream. As the final mission involves dreams at many levels, a kick must be administered at each level to rouse the dreamers from the next level in the sequence. 

• Level 2 to 1: Van driving off the bridge. The original plan was to make use of the impact with the barrier, but this impact was "missed" by the dreamers in Level 2. The second kick came when the van hit the water.
• Level 3 to 2: The explosion under the elevator forces it to rocket upwards, hence simulating gravity. The moment the elevator hits the top the acceleration stops, and the characters are thrown upwards.
• Level 4 to 3: Exploding the base of the fort should be sufficient to bring dreamers back from Level 4 (though it might be a little overkill!).
• Level 5 to 4: There is no Level 5, so there are no dreamers to be "kicked" back to Level 4. Ariadne and Fischer falling off the building seems to play no clear role in the dream mechanic (there is no equivalent at Levels 1-3). Cobb and Saito are by now in Limbo, which operates by different rules (you must die to change levels).

Level 1 to Reality is unknown. The characters will wake up when the dream machine times-out. They must survive several more days in Level 1 before this happens (faking death by drowning helps here, it will calm the militarized projections). Possibly the air hostess administers a kick.

To simulate gravity explosives were planted at the bottom of the elevator, which, on detonation, force the elevator upwards like a rocket. The sudden deceleration caused by impacting the top of the lift shaft would, in turn, simulate a feeling of falling as the characters are catapulted through the air.

The headphone is always placed on the dreamer of the following level and is a cue that a kick is about to take place, urging them to start the kick process for the dream of the next level.

The music will be incorporated by the dreamer into their dream, and all those in that dream will hear it. This acts as a signal to prepare for a kick. It is an instance of the more general phenomenon of something experienced by a dreamer entering the dream in some form - for example, the water of the bath enters Cobb's dream, the champagne drunk by Yusuf on the airplane enters his dream as rain, drowning in the van enters Cobb's limbo dream as the experience of being washed ashore choking, etc.

The team's purpose was to create an "inception", to plant an idea or thought in a dream that would be accepted by the target subject as one of the subject's own ideas. Only in this way would it successfully embed in that person's belief system, and affect their way of thinking in real life. An idea placed in a "shallow" dream level is more easily detected by the subject as an intrusion, as not their own. By suggesting the idea to the subject (Fischer) at the shallow levels, the team hoped to encourage Fischer's own subconscious projections to feed him the idea instead, and so make it more believable for Fischer. With increased depth, Fischer began to feed himself the idea that they presented. This is also known as the power of suggestion, or hegemony (See Wikipedia's article on cultural hegemony, linked below).

They were in fact old when they laid on the train track, but at the time when Cobb was describing the story to Ariadne, he was describing it without giving the detail that they were old. Thus what was shown was the illusion given by Cobb to Ariadne.

At the point Cobb tells Ariadne, he has forgotten that Mal and he had reached old age together. We see him remember this near the end, during the conversation with his projection of Mal in Level 4 (the "ruined city"). Her existence as a projection, and so as part of his own subconscious, is made clear when Cobb tells her she is his own imperfect creation. He then reminds her that his promise to her has been fulfilled: they did grow old together. As she is part of his subconscious, Cobb is basically reminding himself of this. Only now do we see them as an elderly couple.

Because Arthur was the dreamer of that dream. Dreamers can alter their dream at their will.

This is also why Eames was the dreamer of Level 3 - he inserted a shortcut in the plans designed by Ariadne.