We’re first introduced to this concept in the very first novel, in the form of poor Professor Quirrell. Failing to obtain the Philosopher’s Stone on his own, the Dark Lord possesses him. At this time, Voldemort is what the fandom loves to call “Vapormort” or as Voldy himself describes it: “less than spirit, less than the meanest ghost” (GOF, p. 566, UK). What we can glean from this is that he was an incorporeal or nonphysical being. One might go so far as to say he was purely a soul confined to the physical realm.
Here, his ability to possess Quirrell or any other living thing is easily understood; as a soul or pseudo-spirit, he would merely enter a body and take over it. This fits the stereotypical understanding of possession found in media.
Next let us look at Chamber of Secrets, and Ginny Weasley’s possession. This example of possession is much more interesting, because we have a fragment of Voldemort’s soul in a Horcrux (the diary). This soul fragment, however, is still very powerful and clearly has his power of possession…but is it the same? Remember, Riddle was only able to possess Ginny once she had poured her heart out to him and become emotionally attached to the diary, whereas Quirrell and the animals mentioned in Goblet of Fire are easily possessed. Furthermore, Quirrell was conscious of the possession, while Ginny was not.
The last example of possession is when Voldemort possesses Harry in the Ministry of Magic. What makes this case curious is that Voldemort is no longer an incorporeal being – his soul has been restored to his body. This means his soul has been “re-chained” to a body, so to speak, and so does not have the freedom of his disembodied state to possess people. How then was Voldemort able to transfer his soul to Harry, and again why was this a conscious possession?
Having laid out the groundwork, it’s your turn, fans. How do you think possession works? What is the difference between possessing someone as a spirit and when one’s soul is still attached to a body? Why are some victims conscious, while others have no recollection?