I was pleasantly surprised that my analysis of what we know about doppelgängers (Doppelgängers: What do we REALLY know about them?) turned out to be a prescient endeavor, given the big reveal about Stefan and Silas in the Season 4 finale. Since we now have this new instance of doppelgängers, I've had a ton of new thoughts running through my head. Here's my attempt at making sense of them.
What we know about the way magic works in the world of TVD is that there must always be a balance. At its foundation, Nature is bound by the laws of the alpha and the omega: that which begins must end; that which is born must die; that which is done by magic must have a means to be undone by magic. Our characters like to call these "loopholes" - vampires, though unaging and immortal for all intents and purposes, have weaknesses and can be killed; the Hybrid Curse, though deemed necessary by the servants of Nature themselves, is still a magical spell and cannot be sustained without a way to break it; and Silas, seemingly invincible in his immortality, could not be suffered to exist without a point of undoing.
I have observed that one of the main points of contention in the "Was Tatia a doppelgänger?" debate is the timeline of events. There is the argument that she had her child before her blood was used in any of the spells, so she had to have been a doppelgänger first in order to pass it on to her child. However, this contradicts what Katherine says about the doppelgänger:
So, was Tatia used to bind the Hybrid Curse because she was a doppelgänger, or does Tatia have doppelgängers because she was used to bind the Hybrid Curse? My two main reasons for favoring the argument that she was a doppelgänger are:
Notice that neither of my main reasons was that Tatia had her child before any of these spells took place... which leads to my next point.
The new information about Silas and Stefan as his doppelgänger led me to consider the notion of bloodlines. At this point, we know far too few specifics about Silas' past (Did he have a child? By whom? Are the Salvatores his direct descendants?**) and so it's very hard to speculate about that part of the equation. But in thinking about this, I began to consider the notion of a "doppelgänger trait" - that is, in order for a doppelgänger line to continue, the descendants in the bloodline must pass that potential on to each generation.
And then I realized that this idea totally contradicts the point of the doppelgänger as a loophole for a spell.
If the doppelgänger is intended as a way to undo a spell and thus maintain the balance of Nature, a discontinued bloodline of doppelgängers would mean a disruption to the balance. Thus, it doesn't make sense to me that the potential for a doppelgänger would be limited to being passed down mother to child in some kind of DNA-related situation. Besides, it's magic, and almighty Nature generally seems to do what it wants. This is the part when the phrase "Nature will find a way" comes to mind (cue Jurassic Park theme music): if a balance has to be maintained, I believe that Nature can ensure that a doppelgänger will exist if it needs to.
Now, I'm not saying we should go crazy and just say that a doppelgänger could then show up in any old bloodline. Pretty much every aspect of this show is touched in some way by the binding power of blood - bloodlines, blood used in spells and rituals, blood as the life force of an immortal, blood siring, and blood in the sense of family and loyalty. So, it would seem to me that Nature could maintain the balance by ensuring that a bloodline would keep the potential for a doppelgänger, irrespective of a line of direct descent. (So, like, if Isobel had a cousin or something... ha-ha)
This leads me to address the introduction of the term "shadow self". In Graduation, the phrase "shadow self" makes its first appearance in the series, not once but twice: Katherine calls Elena her "shadow self" early in the episode when talking to Bonnie, and Silas uses it again when he outs himself to Stefan. This looks to me like a typical setup for introducing new terminology: a character we're familiar with uses the term while talking about something we're also familiar with - Elena is Katherine's doppelgänger, and the synonym "shadow self" is a natural extension that doesn't require much of a leap. But then the question is, why introduce the term at all? Why isn't "doppelgänger" sufficient? This is part of what I hope we come to learn next season, but for now it seems that the reason must have to do with how we think about doppelgängers.
Here is where the speculation becomes heavier than the facts: the term "shadow self" strikes me as something that suggests more of an intimate connection than just looking identical to your 500 year old ancestor. After all, everyone has a shadow, and it isn't something you can get rid of or part with (we'll leave Peter Pan out of this argument). If Stefan is Silas' shadow self, to me this suggests much more of a connection than what we've come to see between Katherine and Elena. So while Katherine may have flippantly referred to Elena as her shadow self, I don't think it's totally accurate, as technically Elena is not Katherine's doppelgänger, but rather they are both doppelgängers of someone else (be that Tatia or a more ancient ancestor). Shadow self, to me, seems like it should be reserved for the relationship between the original person and all subsequent doppelgängers.
Also, the inseparability of a person from his shadow suggests to me an even more sinister connection between Silas and his "shadow self". What that might be... I don't have any solid ideas about that yet.
Okay, forgive the Harry Potter reference, but it's relevant. Sort of. Mostly just a humorous title for this short little section.
All right. I've established my position on how I think doppelgängers are created as loopholes, and how Tatia was not necessarily the "original" of which Katerina and Elena are doppelgängers. I just want to address one more thing before I close this really long discussion post. Regarding the matter of doppelgänger blood as a potent binding agent, I do think that this is just a byproduct separate from the original spell that created the doppelgänger in the first place. That is, when the spell you perform is so powerful and altering that it will upset the balance of Nature, the rare phenomenon of the doppelgänger occurs, and a powerful side effect is that their blood can be used to bind other spells. This makes me curious as to whether doppelgängers have other as-yet-unmentioned uses or abilities... though perhaps not 11 more. (See? Relevance!)
So in case you got lost in my convoluted blathering (I wouldn't blame you), here are my arguments summarized as bullet points:
Here's what I want to know about doppelgängers (and related things) going forward:
ANYWAY, if you just read all of that, bless you. I just have a lot of thoughts and sometimes it's easier to make sense of them by writing it all out... and by that point, it seems a waste not to share it! So, comments are welcome, but do be gentle. Speculating and theorizing should be all in good fun :)