Muggles' Guide to Harry Potter/Magic/Horcrux

Overview
Horcruxes are any object in which a sorcerer may preserve a portion of his soul indefinitely. Anchoring a part of the soul to the earth by placing it in a Horcrux prevents the sorcerer's soul from going onwards should the sorcerer's body die; the effective result is that, given appropriate spells, the sorcerer can be brought back to life. This is considered to be among the darkest of all magic.

Extended Description
In Harry Potter and the Half-Blood Prince, Harry Potter learns how Horcruxes are created by experiencing a memory of Professor Slughorn's in Professor Dumbledore's Pensieve. In order to create a Horcrux, it is necessary that the wizard's soul be torn; the only known act that is powerful enough and damaging enough to do this is apparently for the wizard to commit murder. The torn soul fragment can then be removed and placed into another object; and so long as that object is not destroyed, the wizard can remain alive.

Harry learns at the same time that Lord Voldemort had been intrigued by the possibility of the number seven, which would either mean that he intended to create seven Horcruxes, or that he intended to have seven soul shards, which would mean six Horcruxes. Dumbledore believes at the time, correctly as it turns out, that the intended number of Horcruxes is six. It is unknown at the end of Harry Potter and the Half-Blood Prince how successful Voldemort has been at creating Horcruxes, but we can assume that he did create six and secrete them in various objects. Two Horcruxes have been destroyed – Tom Riddle's diary that Harry destroyed in Harry Potter and the Chamber of Secrets, and Marvolo Gaunt's ring which was destroyed by Professor Dumbledore. A third was apparently eliminated by an erstwhile Death Eater identified only as R.A.B., but this turns out in the seventh book to not have happened. To defeat the Dark Lord, Harry must find and destroy the remaining Horcruxes and then kill Lord Voldemort.

Note that we do not list Horcruxes as having first appeared in Harry Potter and the Chamber of Secrets because the diary is not identified as a Horcrux, by name or function, until Harry Potter and the Half-Blood Prince.

Harry and Dumbledore deduce that the remaining Horcruxes are quite possibly coveted heirlooms of the four Hogwarts House founders; they see how much Riddle covets the two that he has seen in Hepzibah Smith's possession. One of these two, Salazar Slytherin's locket, was originally a Gaunt family heirloom; Riddle's mother had sold it to Borgin and Burke for a pittance, to buy food, and they had sold it in turn to Hepzibah Smith. Riddle apparently stole it back from her and used it as a Horcrux. The other, Helga Hufflepuff's cup, has not been seen since Harry and Professor Dumbledore saw it in Hokey's memory, but it evidently was also stolen by Riddle, and is presumed to have been made into a Horcrux.

Analysis
At the beginning of Harry Potter and the Deathly Hallows, Hermione explains what she has learned about Horcruxes from the books she retrieved from Dumbledore's study. As mentioned above, the Horcrux cannot be destroyed to unbind the wizard from earth until the container housing it is destroyed. Souls are, by their nature, virtually indestructible; a fragment can be sheared away, as mentioned, by the act of committing murder, and that fragment, if contained in an object, causes the object to partake of its indestructibility. Ordinary magic cannot harm a Horcrux, any more than ordinary magic can harm a soul. It is mentioned that Harry destroyed the Diary Horcrux by stabbing it with a Basilisk fang; Basilisk venom is certainly extraordinary magic, given how uncommon basilisks are. Of the six Horcruxes destroyed, it turns out that five are destroyed by Basilisk venom in one form or another, and one by Fiendfyre.

One plot point left hanging at the end of Harry Potter and the Half-Blood Prince is a missing Horcrux. Dumbledore and Harry have clearly discovered where the Horcrux is hidden, but the Horcrux itself is gone, replaced with a substitute locket by one "R.A.B." Both the substitute locket, and the unknown "R. A. B." (presumed to be Regulus Black), are keys to the "real" locket's whereabouts. In Harry Potter and the Order of the Phoenix, the Black family house is being used surreptitiously as headquarters for the Order of the Phoenix. When Sirius and Molly undertake to clean the house, Kreacher, along with Mrs. Black's mad screaming portrait, undermines this effort. Listed among the objects being discarded is "a heavy locket that none of them could open." Harry, having retreated to Grimmauld Place after the Ministry has fallen in Harry Potter and the Deathly Hallows, sees Regulus' name on a bedroom door, and deduces that this must be the "R.A.B." connected to the substitute locket. After fruitlessly searching Regulus' room, Hermione recalls the locket that they had earlier tried to discard. The locket had been hidden by Kreacher, then stolen by Mundungus Fletcher, who was busily looting 12 Grimmauld Place during the early parts of Harry Potter and the Half-Blood Prince. Mundungus has, in turn, had it extorted away from him by Dolores Umbridge, resulting in Harry making an expedition into the Ministry to retrieve it.

As noted above, Voldemort split his soul into seven parts. In many cultures and religions, seven is a significant number, possibly because it is the "most magical number", as Riddle says; hints of this magical power likely strayed into our Muggle world.

Questions

 * 1) Can a Horcrux be a living object? Could it be a liquid?
 * 2) How exactly are Horcruxes created? Does the Horcrux have to be related to the victim of the Killing Curse cast by the sorceror creating the Horcrux?
 * 3) In what dark magic book did Tom come across the term "Horcrux"?

Greater Picture
For a list of the Dark Lord's Horcruxes, see Horcruxes.

Obviously, Horcruxes are central to the story, and the location, and destruction, of these will be critical.

We believe, or rather Dumbledore does, that there were originally intended to be six Horcruxes, thus giving Voldemort seven soul pieces – one in his corporeal body, and six extras. While the uninitiate would suppose that one of these would have been used to reanimate him after his attempt to kill Harry resulted in the death of his body, this turns out not to be the case. Apparently, while the soul is physically split, such that part of it resides in an object external to the wizard, there is still a psychic linkage, and the wizard's soul cannot leave the Earth while the shard, locked in an object, remains. Thus, the main part of the soul remains present after the body dies, wandering unhoused through the world. It is this unhoused soul, taking control of various animals in Albania, that is all that remains of Voldemort until Professor Quirrell runs into him, and for the two years between Quirrell's death and Pettigrew's return.

The first Horcrux, the diary, was actually the second one made, and was perhaps somewhat less valued by Tom Riddle. This may be why it was devised as a path to immortality and also as a weapon. The author has stated that this Horcrux was created by Moaning Myrtle's death, killed by the Basilisk. It is interesting that this Horcrux was aware of things that had happened after its creation; it could show Harry the discovery of Hagrid and Aragog, which happened the day after Myrtle's body was discovered.

We do not directly know whose death was associated with any of the other Horcruxes, and at the end of Harry Potter and the Half-Blood Prince we know for certain of only one other Horcrux, the Peverell signet ring. We learn that the ring is a Horcrux during that book, when Dumbledore tells us that he has destroyed it. The remaining four are uncertain until the seventh book, though Dumbledore's guesses about three of them do prove accurate. Until Harry retrieves and destroys them, we cannot be sure that Voldemort has placed Horcruxes in either Salazar Slytherin's locket or Helga Hufflepuff's cup, but by the end of Harry Potter and the Half-Blood Prince we are aware that Voldemort wanted these items, presumably for that purpose; and the fact that the artifact retrieved at the end of Harry Potter and the Half-Blood Prince is a locket does indicate that Slytherin's locket likely is now a Horcrux, as the R.A.B. who removed the Horcrux is likely to have put something similar in its place.

Until the seventh book, we are unsure of the fifth Horcrux; we do not yet have any theory as to what it could be or how it was created. One fan site had suggested that the artifact in question is Rowena Ravenclaw's wand, and that this is the "one, solitary wand" that rests in Ollivander's shop window; this was suggested to have something to do with Mr. Ollivander disappearing in Harry Potter and the Half-Blood Prince. In that case, the murder that created the Horcrux could well have happened in Diagon Alley. This turns out to be incorrect; the fifth Horcrux is an artifact that we only learn about in the seventh book: Rowena Ravenclaw's lost diadem.

We believe Voldemort intended to create the sixth and final Horcrux by killing Harry Potter. It is possible that he was carrying the artifact he meant to convert into a Horcrux with him, and it would have remained when he died. It could have been found in Godric's Hollow when Harry goes to investigate there. Harry, however, never entered his parents' house, only looking at it from outside the overgrown hedge.

Thwarted by Harry, Voldemort apparently used Bertha Jorkins' death to create a final Horcrux, which Dumbledore believes lies within Nagini. There is a risk, of course, in that a living being, with a mind of its own, will interact to some extent with the associated soul fragment, but Voldemort would have been low on resources at this point, and only had a small selection of artifacts to choose from. In passing, we do see one of Dumbledore's very rare mistakes here; Dumbledore says that Voldemort used Nagini to kill Frank Bryce, and may have created a Horcrux at that time. This would imply that it is not necessary to kill someone directly in order to create a Horcrux; ordering another to do the killing would be sufficient, perhaps with the proviso that the being ordered to do the killing must not be sentient. However, reading the end of chapter 1 of Harry Potter and the Goblet of Fire, we see that in fact Voldemort killed Frank Bryce with the Killing curse. Thus, even if Bryce's death had resulted in creation of a Horcrux, we wouldn't know if directly murdering someone is necessary to the Horcrux creation spell. The author's saying that the Diary Horcrux was made by way of Moaning Myrtle's death, which was caused by the Basilisk, rather than directly by Riddle, does rather confirm that using an agent to commit the murder does not prevent a Horcrux being created.