In the interest of not spamming Mit-boy with more comment notifications, I'm only going to issue one response, and your next comment will have to go unchallenged. If you find this discussion interesting, however, and would like a response, note me.You make three points here, and I think I will respond to them in reverse order.

In the first place you note that the Siren's Equestrian forms were apparitions. This, I think, is something that complicates the issue and leads us to agnosticism rather than offering positive evidence for your case. Even if we assume, without deciding, that we are to take these visions of the Sirens and of the manifestations of the Rainboom’s attacks (e.g. the Diamonds that emit from Rarity’s keytar and the Butterflies that emit from Fluttershy’s tambourine), as non-physical, I do not think that immediately we can conclude that the apparitions were a mere extensions of power and that we are not to assign any mind or personhood to the apparent Sirens. I say this because you cite as evidence the “big alicorn,” as though we are obviously supposed to take him as being physical and non-personal. I think this, however, is far from clear. And I would offer the counter-interpretation that we are not to take the “big alicorn” as a manifestation of the Rainboom’s power, but as an incarnation of Harmony, summoned by the union of the seven (the Six and Sunset Shimmer), and through whom the Elements receive their power. I do not mean to state this such that I am ready to defend this particular view tooth-and-nail, but I think it shows that we merely arrive at uncertainty on this point. It is far from clear whether we are to conclude these visions are non-personal merely because of their appearance.



Secondly, I think you have misunderstood what my positive case in fact is. I do not mean at all to say that the apparent Sirens were hosting the human Sirens, as though the Sirens of Equestria and the Sirens of the human world were different persons; that would be ridiculous. My position is that the Equestrian Sirens (the creatures defeated by Starswirl) and the human Sirens (The Dazzlings) are single persons distinguished merely by their natures. That is, each Siren has an immortal nature that appears in Equestria and a mortal nature that appears on Earth, and that these natures give them power to exist in their respective worlds. Without her human nature, no Siren could appear in the human world, and without her immortal nature, no Siren can appear in Equestria. For each Siren, these separate natures are not to be thought of as comprising more than one person; and that if one nature is destroyed, the person remains, even though they lose the properties and powers that the nature provided.



For this reason, I am quite willing to admit, for the sake of discussion, that the Siren’s gems are to be thought of as organs, through which the Siren’s manifest their immortal natures in the human world as forms. This does not show, however, that the gems and the immortal natures of the Sirens are the same entities. For, per your analogy, if a unicorn loses her horn, the magical nature within her does not die, but the power to use that magic does. It seems that it is for this reason that the Human Six are able to manifest their magical forms in the human world: because their Equestrian natures remain.