Hopefully, this edition will be much shorter than the last one, in order to make this an easier read. Since the old one was published, we've gotten much more information on the Avatar, so an update to its dynamics is long overdue. Much of the speculation in the previous edition was proven true following the Beginnings episodes, so some things have been removed, and some have been elaborated on. If there is a conflict of information between this editions and the last, assume the most current version is correct. Also, just because something wasn't repeated in this version, doesn't mean it doesn't still hold true. Read on, and don't forget to let me know what you think!
Dynamics of the Avatar
Over the course of the series, there's been a fair amount of ambiguity on how the Avatar actually works. We've seen various incarnations talking to each other, the terms "reincarnation" and "past lives" were used, and then there was the whole hoopla of the Avatar state. But now thanks to book 2, we finally have some answers, and the first Avatar as well, which was very exciting, and something we've been wanting to know about.
Before I say anything further, I should define some terms that I'm going to be using.
1.) Soul: Basically, your self. You are your soul, and you reside in your body, which is just a shell. Your soul is what defines who and what you are, it is your consciousness, it is the innermost essence of your being, synonymous with the Hindu term "Atman." (forgive me for any spelling errors - also, I'm not very well versed in Hinduism, so if someone who is can add more or correct the existing information, it would be most welcome).
2.) Spirit: When used in reference to someone's "spirit", it means the same thing as soul. It also is the term used to describe the disembodied entities that reside in the Spirit World.
3.) Reincarnation: The process of one's soul, upon death, moving to a new body to live a new life. Usually, or at least in this show, when one is reincarnated, they are basically "wiped" of their past life, and upon rebirth, might as well be a different person, except, well, they're not.
4.) Avatar Spirit: Raava. (or Vaatu). Despite what the Avatar article says as of this writing, Raava is the Avatar Spirit, as she is what makes the Avatar the Avatar. (in case you're wondering, the Avatar article implies that just the avatar spirit moves on in the process of reincarnation, which isn't true, as i will show in a moment.)
5.) Avatar: the human that is bonded to the Avatar Spirit. Avatar is a term that means "incarnation" or "manifestation." Hindu gods will sometimes manifest as avatars to come to earth and enforce their will. An avatar can also be someone or something that enforces a god's will for them. (again, feel free to correct me if you know better.) So in the show, the Avatar is literally Raava's avatar.
Now, let's begin. The term reincarnation has been used so many times in the series that we cannot ignore it: The human part of the Avatar is a single soul. Wan is Korra, and all the others. (Hell, Avatar Extras said exactly that - but with Roku and Aang). When Wan fused with Raava by touching the spirit portals, their souls became intertwined in such a way that death of the body could not separate them. Thus, upon death, since Raava cannot "die" as humans know death, they are reincarnated together as one. We know this because Harmonic Convergence is required for two souls to merge. If Raava were to find a new human each time, meaning that Wan and Korra are different people/souls, she couldn't merge with them, and we wouldn't have an Avatar. Thus, it is the same human soul that Raava has been bonded with the whole time. If you still don't believe me, there's plenty of other evidence throughout:
"I am a part of you."
-Roku to Aang, "The Winter Solstice Part 2: Avatar Roku"
"Aang, you are me."
-Roku to Aang, "The Promise Part 3
"She is connecting with her deepest Avatar memories. She must confront her own past..."
-The Shaman on Korra, "Beginnings Part 2"
"We will be together for all your lifetimes."
-Raava to Wan
-Korra in the spirit world upon seeing the teapot Wan used to carry Raava, "A New Spiritual Age"
"You used it to carry the light spirit around before the two of you became one."
-Iroh to Korra, responding to Korra recognizing her teapot, "A New Spiritual Age"
And that's not all of it either. Korra recognized Iroh, even though she'd never met him in her current life. Keeping that in mind along with the teapot quote above, the Avatar can clearly, after reincarnating, still recall some residual memories of his or her past life, indicating that these memories must be stored in the unconscious mind. The past Avatars are nothing but memories of the current. It is important to mention that, per Darkness Falls, that it is Raava that allows the Avatar to retain those memories, but I'll talk about that more with the Avatar state.
So, now that we've established that they are one, let's address some of the situations where it seems they aren't. The biggest instance of this is the fact that we've seen incarnations talking to each other. However, in every one of those instances, it was the current talking to a past avatar. It seems that the past Avatar present is merely a memory, animated somehow for the current to talk to. But wait, what about the past Avatars in the Spirit World? Glad you asked. :)
Despite what the Spirit World article says as of this writing, the past Avatars do not, in fact, live there. The only proof for this that the article provides is the game titled "Escape from the Spirit World". However, nothing in that game suggests that the past Avatars live there. In every instance of a past Avatar in the spirit world, the current Avatar was there first, indicating that the past one was merely projected just like every other time the Avatar talks to a past life. In fact, two of the four Avatars Aang talks to in that game just appear out of thin air on screen, showing that they are projected, instead of living there. Besides, you can't be in two places at once, and we've already established that the Avatar is one being fused to Raava.
Well, this post is getting a little longer than I intended... If you're still with me, thanks for reading! :p Let's talk about the Avatar state. The earliest explanation we got on the Avatar state was Roku saying, "The Avatar state...is designed to empower you with the skills and knowledge of all the past Avatars." So it seemed that it was some confusing mess of learning to master your own unconscious mind. But in beginnings, we learn that it is in fact Raava. Raava, when passing through Wan's body, gave him a burst of power, and after they fused, that is what the Avatar state is: a burst of power, likely from adding Raava's chi to Wan's. (or whatever his name is...ya know, reincarnation and all.) It could also be that she is temporarily transforming him slightly, as other spirits were seen doing to other humans. (that would also explain what the deal with Unavaatu was.) Although the burst of chi and the transformation things are unconfirmed, we still know that the Avatar state is a power boost from Raava. Roku's past lives thing still holds true though: it seems that when Raava provides the burst of power, she also allows the Avatar to consciously remember his past lives, at least for the duration of the state. Before the Avatar has mastered the state, it is Raava who is controlling the body and bending while in the state, which is the reason that it is "continuous": Raava has to actively be doing something. After mastering the state however, it is the Avatar who draws on Raava's power at will and controls it and their body, which is the reason we've seen the state last a varying amount of time when used by a fully realized Avatar.
What happened in Darkness Falls? Raava was torn from Korra, and then destroyed. Since Raava was destroyed, Korra could no longer retain her connection to her past lives, as it was Raava who allowed her to do that. Aang wasn't really talking to Tenzin, Tenzin was just hallucinating. We know this because "Aang" turned into Tenzin, something that Aang could never do. Please don't ask me to explain the dues ex Jinora, that's not in the realm of the Avatar And Things That Make Sense.
Now this next paragraph I'm just going to copy from the old edition because I think it is worth retaining:
When the avatar's body takes on the form of a particular past life (like when Aang chanelled Kyoshi in "Avatar Day") his mind is simply switching which lifetime's set of memories are conscious. When he calls a past life out of his body (as in the sozin's comet finale) he is projecting unconscous memories for him to talk to (much like what happens in the spirit world). When Korra was kidnapped by tarlock and had memories of Aang, what was basically happening was that Korra's memories from that lifetime were coming to her conscous mind without her having to project them. She is the first incarnation of the avatar that we have seen able to do this.
Well, I think that's all I have for now. If anything else/new comes up, I'll be sure to work it in. If you have any questions, want me to explain something, or think you found a hole in my argument, let me know! I love talking about this stuff!