Why 4 Horcruxes left, and not 3??

[spotsgal]

No: HPFGUIDX 142095

> chrusotoxos
> I thought at first that the seven parts of the Voldemort's soul were 
> all little Voldie, and that from each of them a new Voldemort could 
> reborn if the 'true' one was killed (as in Godric's Hollow). But 
> appearances point to something else: it seems that Horcruxes are 
> different parts of soul, parts that the person won't be able to use 
> again, the good parts of him.
> Dumbledore agrees with this when he says that Voldemort grew less 
> human with the passing years; JKR agrees when she says that we'll find 
> out why Voldemort is so evil.

Christina:

I don't think that this is what Dumbledore is talking about.  We know
that killing splits the soul and that a horcrux is a soul-part's
external form.  I hesitate to start picking the math, because we all
know that that isn't JKR's favorite subject, but here I go anyway--

Now, while I don't believe it is strictly stated in canon, I think it
only makes sense that each killing would tear one's soul in half, so
let's run with that for a while.  For simplicity's sake, let's just
say that the only murders Voldemort commits are used for
horcrux-making.  That means his first horcrux would have 1/2 of his
original soul in it, and Voldemort would retain 1/2 of his original
soul.  For the second horcrux, Voldemort would split the amount of
soul he currently has in two again, meaning that his second horcrux
would have 1/4 of the *original* soul and Voldemort would have 1/4 of
his *original* soul.  For horcrux #3, Voldemort's 1/4 of a soul splits
in half again, so the horcrux and Voldemort each have 1/8 of the
original soul.  And so on and so forth.  In this respect, every time
Voldemort kills and makes a new horcrux, the amount of soul he retains
is less and less.  Also notable is the fact that it seems that each
horcrux is less powerful than the one before, since the amount of soul
a horcrux contains is half the amount that the last horcrux contained.
 Could this explain the extra power that Tom Riddle's diary possessed?  

Now assume that killing doesn't rip a soul precisely in half, but
rather cuts of a chunk of unknown size.  Still, Voldemort would
progressively have less and less of his original soul as he went on
and made horcruxes.  I think a lot of people assume that each horcrux
contains 1/7 of Voldemorts soul, which doesn't make any sense (how
would his soul "know" how many horcruxes he wanted to make)? 
So...Dumbledore's statement that Voldemort grew less human makes sense
because he slowly lost huge chunks of his soul as he made his horcruxes.


Christina