It doesn't rely on Quirrel telling the truth, it concludes that something (which Quirrel happened to say) is true.
This turns out to be an important distinction, at least in my own life. Trying to decide a priori whether someone is lying almost never works for me. (Paul Ekman, I'm not.) The answer always turns out to be "maybe," and I frequently end up biased by whether I like the person, whether I've caught them lying in the past, etc.
It works better for me to decide what I think is or might be true, regardless of who said it.
Q1: Did Quirrel try to kill Bahry? It seems dumb for him to do so... it achieves no goals I can think of that couldn't be achieved more easily, and it makes his stated goal of not being noticed far more difficult. So either (A) he was being dumb, (B) his actual goals are entirely opaque to me, or (C) he didn't try to kill Bahry.
Q2: Did Quirrel try to achieve some nonlethal goal using an AK, as he claimed? That doesn't make a lot of sense to me... like you, my intuition is there have to be better weapons for that purpose. So either (A) he was being dumb, (B) my intuition about Battle Magic is wrong and AK really is a sensible spell to feint with, or (C) he was trying to kill Bahry, see Q1.
I'm prepared to eliminate both A's on narrative grounds... the author seems committed to not having Quirrel do dumb things. Both B's are plausible, so my jury is still out... but I have more confidence in my intuitions about human goals than about Battle Magic, so if I have to choose I choose (Q1-False, Q2-True). But there's a lot of uncertainty there.
If this were reality, I could (eventually) reduce the uncertainty by researching Battle Magic -- is it ever tactically plausible to use an intentionally nonlethal AK as a forcing move? If not, then my tentative decision changes; if so, I hold it more strongly.
Of course, Harry does not have the time right now to consider that (or maybe he already knows enough to make it seem plausible, and the audience simply isn't privy to that).
Anyway, my primary point here is that it's often more useful for me to think about the events that happened and what seems a more plausible explanation, than to think about whether the person reporting them is lying or telling the truth. Accuracy is not reversed deception.
If this were reality, I could (eventually) reduce the uncertainty by researching Battle Magic -- is it ever tactically plausible to use an intentionally nonlethal AK as a forcing move? If not, then my tentative decision changes; if so, I hold it more strongly.
Interestingly, my intuition tells me that AK is perfectly sensible to feint with. It's like putting someone in check in chess - they have to get out of it by one of a very few limited ways. To not do so would be checkmate and the end of the game, much like dying is the end of the duel.
(And there ar...
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.