The theory assumes that both Sebastian and Ciel are the only one who knows about the lie.
Also, it's interesting to note that Sebastian can't lie, and he never called him by the name Ciel. Though of course the logical way to see it is that he can only call him bocchan. Just thought it was worth mentionning.
He also laughed numerous times about it (only an interpretation):
Ch.2
p43-44 Sebastian recalls the scene in which YM claims that he is 'Ciel', the head of the Phantomhive family, and smiles cynically over it.
Ch.61
p24 Sebastian asks his name and YM hesitates for a while before he answers: "My name is ... ... Ciel. Ciel Phantomhive. The one who will inherit the house of Earl Phantomhive." -> Sebastian smiles cynically (since he knows that the child is lying) and replys: "Fufu... Just as you wish"
Ch.62
p7-8 "As Ciel Phantomhive (...) I swear I won't lose."/"You told me not to lie, yet you seem to be quite a liar" (YM/Sebastian)
Scratch the "only ones", we don't really know x)
But at least Sebastian knows.
Wait, so Sebastian's never called Ciel by his actual name?
Well, no. Not a single time.
And I don't think Undertaker has either now that I think about it. He keeps refering to him as "Young Earl".
Maybe the Undertaker know's he's a twin, especially since he knows a little about Ciel's family (regarding the lockets and all). But I think it's interesting that Ciel hasn't been addressed as Ciel by Sebastian yet.
Interesting theory, but, in the Victorian era, anyone who is considered a servant and has the audacity to call their master by their first name is thought to be extremely disrespectful and could be grounds for dismissal from employment. They were very formal when addressing anyone 'above their station', so it's not surprising that Ciel has never been called Ciel by Sebastian. (Just my thoughts here)
Same goes for Undertaker. His rank would be FAR below Ciel's, so he'd get into trouble for addressing Ciel by his name. Sure, he probably doesn't give two shits, but Ciel probably would have called him on it if he tried it in the past (which we wouldn't have seen since it'd be pre-series start). So now Undertaker calls him "Young Earl", which could very well be read ironically to indicate that the respect that should be there isn't. (Or if one want to go there, that he know's Ciel isn't Ciel. But if there WAS a twin, and he died, then Ciel IS the Earl so that theory isn't all that solid since calling him by a title that is his to show he knows someone else had it before is pointless - of course someone had it before, it's called a father at the very least.)
Cool! I should have figured that though! It only makes sense.
Indeed. It's just interesting. Anyone can find another way to interpret things in this manga 8).
Well, butlers at that time were refered by their last name alone. The servants should refer to him as Mr. Michaelis. It isn't the case.
Though a bit unrelated, but we could question the manga's historical accuracy, I mean everyone seems to want to back up eveything with it.
I think people have to understand she isn't creating a "historically accurate piece", she's creating a fantasy world based on an era. In Victorian London, childs didn't make deals with demons, Reapers didn't leap about with lawn tools, the queen didn't wear cool shades, clothings weren't revealing at all.
She did an insame amount of work and research to create her world. But she goes to show that it's her own creation and that she's taking liberties.
Also about Undertaker, well for someone who doesn't want to get into trouble, he has no sense of personal space when it comes to Ciel. He tends to get a little too close to him, I don't think it was acceptable to an Earl in the Victorian Era.
The undertaker is evil, right? I think he knows a great deal of things about Ciel.
Well, that was my point. Though I wouldn't say he's outright evil, he just isn't on the good guy's side. And he does insist on never calling him by his name, even when he's talking alone. It doesn't prove much, but it did trigger my attention.
He didn't seem all that far below Ciel to me, though he probably did to a certain point. Aside from refering to him as "Young Earl" I guess, and even then maybe "young" could seem deplaced (what do I know), he talked very casually to him and embarassed him a lot of times like it was his own right.
*deplaced -> innapropriate
Damn me trying to make out words out of French :P. There's just so many that are very similar and follow the same pattern between English and French, it can get quite confusing aha
I know there's always been an absent motive as to why the twin theory even came about, and as to why Ciel would even switch places, and I came up with a theory.
If the twin theory is correct, than isn't that bad for Sebastian? Because he made a deal with Ciel Phantomhive, and if Ciel isn't really Ciel, than Sebastian's working for nothing.
I know it sounds strange, but Sebastian made a deal with Ciel Phantomhive, and if Ciel isn't him, then Sebastians just being fooled (because Sebastian doesn't know it's not Ciel). So we can assume that Young Master Ciel took original Ciel's title in the spur of the moment in order to avoid making an actual deal with Sebastian, thus his soul is saved.
And maybe that's why he's so chill when he says he'll die and stuff like that, because he knows that he's not really Ciel, and that he's just tricking Sebastian.
From what I know of stories dealing with making deals with demons, occults, etc., your name is one of the strongest powers an entity of the supernatural nature has over you, and the same actually goes for it, (which may also be a reason why Ciel doesn't know what Sebastian's real name is), so with the name being a tiny loop hole in the contract, than it makes everything Sebastian's done useless.
Also, this is assuming that Ciel took his entire twin's identity. Though, i'm very certain that this in itself has tones of loopholes, as the seal was placed on Ciel's eye, thus no matter who he says he is, Sebastian will still get him, but I suppose that could be a hidden intent that just failed miserably (for Ciel, that is).
But i feel like Ciel has a trick up his sleeve. Just an opinion/theory though.