if this happened, it would seem like we would have seen that happen before, at some point in time.
Why? Someone having multiple Horcruxes is explicitly unprecedented, and having the Killing Curse not kill someone it hits and instead rebounding to hit the caster is explicitly unprecedented. An unprecedented result isn’t particularly improbable.
Yes, “accidental Horcrux” is inherently less probable than the broader category of “random magical accident”, but that’s only because “accidental Horcrux” is a subset of all possible “random magical accidents”.
On your first point: It’s not the making of a Horcrux which rips apart the soul, it’s murder. Although multiple Horcruxes are unprecedented, multiple murders are not. Since it’s the ripped apart soul which causes accidental Horcruxes, if Horcruxes can accidentally be made then we’d expect at least a few of the people in Azkaban to have accidental Horcruxes, and for this to be known about. On the other hand, if making Horcruxes requires complicated Dark Incantations (and it seems like it would) then that’s also evidence against.
On your second point: right, but the absence of any evidence which makes “accidental Horcrux” more probable should make “accidental Horcrux” even less probable than the broad category of “generic unexplained random magic” because when good authors want to write about specific pieces of magic they leave evidence supporting that specific thing. It made sense, since she didn’t support any one possibility of accidental magic over another, to believe that she wouldn’t specify the mechanism at all and that perhaps there was no specific mechanism she had thought out.
That’s not relevant, I shouldn’t have said Azkaban specifically but that shouldn’t undermine my point. Some people who were mass murderers, many, actually, I assume, and have been hit with Killing Curses (or have died in other ways, I don’t know why the Killing Curse specifically would be more likely to fragment a soul than other forms of death?). None of those murderers stayed alive because of accidental Horcruxes.
[...] on the night Lord Voldemort tried to kill him, when Lily cast her own life between them as a shield, the Killing Curse rebounded upon Lord Voldemort, and a fragment of Voldemort’s soul was blasted apart from the whole, and latched itself onto the only living soul left in that collapsed building.
If the only accidental Horcruxes made this way are similar to Harry, there wouldn’t have been noticeable effects (assuming most people who aren’t expecting it would cope significantly less well than Voldemort), and the shade left over would have passed on when the living Horcrux died. (The actual requisite for destroying Horcruxes is “damaged beyond magical repair”.)
Or possibly there wouldn’t have been a shade at all- maybe a mass murderer who didn’t have a Horcrux to begin with would just die the same way everything else does when hit by an AK.
Or maybe nobody else in history had flayed his soul into ~3.125% of its original glory.
Yes, it’s murder that rips the soul—but it’s the process of creating a horcrux that takes half of what’s left and seals it somewhere else. If you aren’t making horcruxes, then you get a soul that’s heavily damaged, but it isn’t lacking pieces, it’s just torn up. With Voldemort, you get a soul that barely has anything left and is constantly being torn up.
Even if you don’t buy the death-mid-horcrux-ritual theory, does it make sense how damage that would normally be taken without notice could rip off whole sections of a soul with ~3% of the...size?...of the souls of even the worst non-horcrux-using mass murderer?
Why? Someone having multiple Horcruxes is explicitly unprecedented, and having the Killing Curse not kill someone it hits and instead rebounding to hit the caster is explicitly unprecedented. An unprecedented result isn’t particularly improbable.
Yes, “accidental Horcrux” is inherently less probable than the broader category of “random magical accident”, but that’s only because “accidental Horcrux” is a subset of all possible “random magical accidents”.
On your first point: It’s not the making of a Horcrux which rips apart the soul, it’s murder. Although multiple Horcruxes are unprecedented, multiple murders are not. Since it’s the ripped apart soul which causes accidental Horcruxes, if Horcruxes can accidentally be made then we’d expect at least a few of the people in Azkaban to have accidental Horcruxes, and for this to be known about. On the other hand, if making Horcruxes requires complicated Dark Incantations (and it seems like it would) then that’s also evidence against.
On your second point: right, but the absence of any evidence which makes “accidental Horcrux” more probable should make “accidental Horcrux” even less probable than the broad category of “generic unexplained random magic” because when good authors want to write about specific pieces of magic they leave evidence supporting that specific thing. It made sense, since she didn’t support any one possibility of accidental magic over another, to believe that she wouldn’t specify the mechanism at all and that perhaps there was no specific mechanism she had thought out.
None of the people in Azkaban have been hit with Killing Curses, though.
That’s not relevant, I shouldn’t have said Azkaban specifically but that shouldn’t undermine my point. Some people who were mass murderers, many, actually, I assume, and have been hit with Killing Curses (or have died in other ways, I don’t know why the Killing Curse specifically would be more likely to fragment a soul than other forms of death?). None of those murderers stayed alive because of accidental Horcruxes.
Maybe they did. Again, the quote is
If the only accidental Horcruxes made this way are similar to Harry, there wouldn’t have been noticeable effects (assuming most people who aren’t expecting it would cope significantly less well than Voldemort), and the shade left over would have passed on when the living Horcrux died. (The actual requisite for destroying Horcruxes is “damaged beyond magical repair”.)
Or possibly there wouldn’t have been a shade at all- maybe a mass murderer who didn’t have a Horcrux to begin with would just die the same way everything else does when hit by an AK.
Or maybe nobody else in history had flayed his soul into ~3.125% of its original glory.
Yes, it’s murder that rips the soul—but it’s the process of creating a horcrux that takes half of what’s left and seals it somewhere else. If you aren’t making horcruxes, then you get a soul that’s heavily damaged, but it isn’t lacking pieces, it’s just torn up. With Voldemort, you get a soul that barely has anything left and is constantly being torn up.
Even if you don’t buy the death-mid-horcrux-ritual theory, does it make sense how damage that would normally be taken without notice could rip off whole sections of a soul with ~3% of the...size?...of the souls of even the worst non-horcrux-using mass murderer?