The Pensieve is, in my opinion, one of the magical world’s most fascinating inventions, because it appears to break not only laws of the physical world, but also laws of the human psyche.
My first question about the Pensieve is: when a person removes a memory from his or her head to put in the Pensieve, are they still able to access it in their minds? Snape’s Occlumency lessons with Harry in OOTP make me want to say no. Before each of Harry’s lessons, Snape removes three memories from his head and places them in the Pensieve, presumably to protect his privacy if the Legilimency backfires (as it does when Harry uses the Protego charm). On a second glance, however, this doesn’t make much sense. In Harry’s lessons with Dumbledore, the two of them discuss Dumbledore’s memories while the memories are in the Pensieve, not in Dumbledore’s head. This would be quite difficult to do if Dumbledore could not remember anything about the memories that he put within the Pensieve. It would also be significantly harder for him to convince witches and wizards like Bob Ogden or Hepzibah Smith to part with their memories if they would have complete amnesia of the event.
Another aspect of the Pensieve that confuses me is that the Pensieve rebels against the laws of how memory works. Psychology tells us that memories are not purely accurate representations of events that have happened in the past. We tend to remember only the gist of an event, and fill in the details based on our expectations of what should have been there. The original trace fades, and as we recall events and retell stories, more and more of our memory becomes fabricated and simplified. The Pensieve, however, shows events exactly how they occurred, with all the surrounding details and even sometimes more. Harry, for example, is able to listen to his father’s entire conversation with his friends even though Snape, whose memory it was, probably did not hear it (Snape’s Worst Memory, OOTP). The Pensieve also shows us events not through the perspective of the person who experienced it, which would make sense if it was a true memory, but through the perspective of a third party. Admittedly, there are some people who see their own memories through an observer perspective, but the observer in the Pensieve is an independent actor who is not always focusing on the person whose memory it is.
We are given one situation where a memory in the Pensieve is not purely accurate.This memory is Professor Slughorn’s recollection of telling Tom Riddle about Horcruxes. It is common for people, over time to attempt to recall uncomfortable memories of themselves in a more flattering light. Slughorn’s version of this, however, is not particularly normal. His involves thick white fog and loud, booming voices, which are not features that people typically incorporate into their memories. Dumbledore describes this as, “[Slughorn] has tried to rework the memory to show himself in a better light, obliterating those parts which he does not wish me to see. It is, as you will have noticed, very crudely done, and that is all to the good, for it shows that the true memory is still there beneath the alterations” (A Sluggish Memory, OOTP). This description of Slughorn changing his memory makes me think that Slughorn did not “rework” his memory in a normal, natural way, but rather tampered with it through magic. When Harry finally gets Slughorn’s “true memory” it is just as accurate as any other memory they have viewed in the Pensieve.
All of this evidence convinces me that the Pensieve does not actually deal with memories, at least in the way that we think about and experience our memories. It is far more magical than that. The Pensieve accesses a moment in time, one that we happened to be a part of, and recreates that moment in time for us to watch. This makes me believe that, as far as the Pensieve is concerned, people are able to put this exact recreation of an event into a Pensieve and still keep their own biased, limited, inaccurate perspective. They are not able to access the accurate version of events without the help of a Pensieve, but they are able to relive their own memories within their head whenever they want.
What are the implications for this theory, then, on how Legilimency works? If Snape was trying to protect himself from Harry’s intrusions by putting the true, accurate “memories” in the Pensieve, then that suggests that Legilimency does not access our own changed, subjective accounts, but rather something more fundamental underneath. There is some evidence to support this view. During Harry’s Occlumency lessons we are told that he is forced to “relive a stream of very early memories he had not even realized he still had” (Seen and Unforeseen, OOTP). If these memories are early enough, it is possible that Harry would not be able to consciously or accurately recall them by himself. However, through Legilimency, or the Pensieve, he is able to “relive” them. When Harry breaks into Snape’s mind and observes his memories he is, once again, from an outsider perspective, watching young Snape, in a way that is similar to the Pensieve. If Legilimency is, after all, allowing access into the purer form of memory, then it is potentially even more dangerous as a weapon, treating the mind like a Pensieve of its own.
On Pottermore, JK Rowling has written about the history of the Pensieve, but she has not addressed any of my questions about how it works. We would need more information from Rowling herself to know if my theory is correct.