I’ve been thinking of doing a series of posts like this were we clear up some canon facts that have been distorted by the fandom. I mostly wanted to do this because I really enjoyed debating and talking about hp but some times when I’m doing that some peoples view of certain characters and events are being informed by complete fanon and it gets incredibly frustrating (I feel like there’s some people here that can relate to that). I like to have well meaning discussions about hp but only if we’re on the same page and someone’s not getting their info from fanfics yknow? So let’s talk about pensives:
Pensives are a magical device used to store and review memories. Often I find while discussing scenes that we see from pensives someone will say something along the lines of “pensives are biased memories, they are showing you the memory from one perspective and that perspective can amplify the emotions felt in that memory which distorts the reality and therefore aren’t an accurate reflection of reality.” But this isn’t canon. I can see where this thinking comes from, human memory is limited and very biased. What I remember from an event my friend can remember in a completely different way. But this is a MAGICAL device that is working outside of what is possible for our brains to achieve. This is why when we look at the pensive scenes in GOF and in OOTP we are seeing details and perspectives we normally wouldn’t be able to naturally. A good example of this is in Snape’s worst memory; we see him giving all his attention to his paper, writing fast and small with his nose close to the parchment, but we also see James, Sirius, Lupin, Peter and Flitwick doing their own thing even though Snape isn’t paying attention to him. Snape most likely can’t see that James is doodling and more importantly what exactly he is doodling from seats away. They are objective realities.
Lets look at a quote from Rowling to get a better understanding:
“Q: Do the memories stored in a Pensieve reflect reality or the views of the person they belong to?”
JKR: It’s reality. It’s important that I have got that across, because Slughorn gave Dumbledore this pathetic cut-and-paste memory. He didn't want to give the real thing, and he very obviously patched it up and cobbled it together. So, what you remember is accurate in the Pensieve.
Q: I was dead wrong about that.
JKR: Really?
Q: I thought for sure that it was your interpretation of it. It didn’t make sense to me to be able to examine your own thoughts from a third-person perspective. It almost feels like you'd be cheating because you'd always be able to look at things from someone else's point of view.
Q: So there are things in there that you haven't noticed personally, but you can go and see yourself?
JKR: Yes, and that's the magic of the Pensieve, that's what brings it alive.
Q: I want one of those!
JKR: Yeah. Otherwise it really would just be like a diary, wouldn’t it? Confined to what you remember. But the Pensieve recreates a moment for you, so you could go into your own memory and relive things that you didn't notice the time. It’s somewhere in your head, which I'm sure it is, in all of our brains. I'm sure if you could access it, things that you don't know you remember are all in there somewhere.”
Source: http://www.accio-quote.org/articles/2005/0705-tlc_mugglenet-anelli-3.htm
So there we go, pensives are objective memory relayers that aren’t biased by the person whose mind it came from.