Magic in the Wizarding World does not work unlike our own science. Think back to Chemistry and balancing those lovely equations. Everything put into chemical reaction had to come out on the other side. I believe this is also how the making/taking apart of a horcrux works.
Formula for a Horcrux:
(Creation of a horcrux)
Murder of Father + DE Sacrifice + Horcrux Death + potion + object + innocent life -->
(Taking apart of horcrux)
Innocent life + Bone of Father + Flesh of the Servant + Blood of the Enemy + potion + object
Murder of Father/Bone of Father (unknowingly given):
The father’s bone cannot be “unknowingly given” when the horcrux is taken apart unless he is already dead. Therefore, I suspect that Voldemort had to kill his father before he could create any horcruxes. Murder tears the soul, but killing the person who gave you life would do something special indeed. Many of the Death Eaters are guilty of murder. Why don’t they all have horcruxes? None of the Death Eaters have killed his/her father, and they must do that before they can take their soul apart.
DE Sacrifice/Flesh of the Servant (willingly given):
We know that in Voldemort’s potion to return to life he needed the “flesh of the servant willingly given.” Why? Because Voldemort needed a willing sacrifice to make his horcrux (he this needed one to take it apart). I am guessing this means that one of Voldemort’s school friends had to either a) commit suicide in his name, or b) consent to Voldemort killing him. The flesh willing given is symbolic of this sacrifice. This step might not equal death alone, however. I am open to suggestions here.
Horcrux Death/Blood of the Enemy:
Voldemort does not kill lightly. He has his DE’s do the dirty work unless a person is posing a significant threat. Why is this? Voldemort does not kill unless it is specifically to create a horcrux (no point in splitting his soul into useless pieces). The horcrux death must be a person posing a significant threat because Voldemort must consider that person an enemy. The Horcrux death is represented symbolically when the horcrux is taken apart by the “blood of the enemy.”
Innocent Life:
Chamber of Secrets makes a unique suggestion about horcuxes: that Voldemort must feed off of another life to remove himself from the object. Tom Riddle was still in the Diary until he sucked the life force out of Ginny. Voldemort must take another life to remove himself from the object. Because we are adding another death to the Taking apart of horcrux side of the equation, there must be another one on the other side for it to equal out. I propose that Voldemort must seal his soul inside of the horcrux with the death of an innocent person on the Creation of a horcrux side.
The Same suggestion that is made in CoS is also made in PS/SS through the use of unicorn blood. Voldemort most drink the unicorn blood, obtained by killing something pure and innocent, in order to remain something that is more than a vapor, something that is able to attach itself to something else. In PS/SS he is able to attach himself to Quirrell by drinking the unicorn blood. In GoF he has attached himself to the form of some extraordinarily ugly baby. Also note that Voldemort is unable to do anything for himself when he is dependent upon the unicorn blood. This could be the supposed “curse” of drinking the unicorn blood.
VOLDEMORT’S PLANS: FOILED AGAIN!
Now I will demonstrate how my horcrux theory works into each of the book where Voldemort attempts to come back to life (PS/SS and CoS).
Sorcerer’s Stone:
I do not think that Voldemort was trying to obtain the Sorcerer’s stone to retrieve his body. How would the Sorcerer’s stone aid him in that, after all?
Voldemort’s Plan in Sorcerer’s Stone:
1. Attach soul to something living, i.e. Quirrell (complete)
2. Get into Hogwarts, i.e. Quirrell becomes teacher (complete)
3. Obtain Sorcerer’s Stone (incomplete)
4. Come back to life GoF style, Quirrell playing the role of Wormtail (incomplete)
5. Use Sorcerer’s Stone to make THE BODY immortal (incomplete)
The difference between a Horcrux and the Sorcerer’s Stone:
A Horcrux contains a piece of a person’s soul. The person can never truly die because a piece of his soul is tied up here on Earth. He can come back to life. Problem: the soul is immortal, the body is not.
The Sorcerer’s Stone makes the body immortal. The soul is not tied to Earth. Whereas with Horcruxes, the body would eventually die (I suspect, this isn’t ever stated) and thus another body would have to be generated. I suspect after 7 lifetimes, the number of horcruxes Voldemort has, Voldemort would die. He is not truly immortal with a horcrux. He is more like a phoenix, but would, eventually die, I believe.
Therefore, Voldemort’s intent was not to use the Sorcerer’s stone to become himself again, but to become immortal in body and spirit after he has gone through the GoF process.
Chamber of Secrets:
Tom Riddle would not be fully “back” after sucking the life out of Ginny Weasley. It is not a substitute for the potion which he used in GoF. Tom Riddle is a stronger version of Babymort. Why did Tom Riddle need to suck Ginny’s life out in the Chamber of Secrets? I suspect Tom planted an illegal portkey down there as a Hogwarts student or perhaps a graduate looking for work. Tom lured Harry into the Chamber of Secrets with the blood message so that he would be able to take Harry with him (to the Graveyard?). One of Voldemort’s followers would have to be there waiting for him (Lucius Malfoy?).
A/N:
So ends my insane theory. It's rather complex, I know. It suggests that it would take a very cruel person, beyond the cruelness we have imagined before. It would explain why Slughorn was so reluctant to speak about it. One expects people to die, and to kill, in a war. Creating a horcrux goes beyond that, however.