This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 118.

Plans for next chapter release:

Ch. 119 (9800 words) will post on March 10th, 2015 at 11AM Pacific (6PM UTC)
Note that the current chapter count goes to Ch. 122.

There is a site dedicated to the story at, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on

Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically:

You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).

If there is evidence for X in MOR and/or canon then it’s fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that “Eliezer said X is true” unless you use rot13.

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Sad ending:

All the students agree to take on the position of Defense Professor de facto.

Next year, all the students die.

When will Harry tell Hermione the truth? I feel like he should insist she learn occlumency first.

This might be a dumb question, but is the specific lesson of the Something To Protect article reflected in these last chapters? If so, in what way?

My take: Harry has QQ('s legacy) and Hermione to protect, and kills dozens of death eaters etc. etc. to make it happen

McGonagall has her students to protect, and commits publicly to doing so, no matter who their parents are, and takes up the role of headmistress (which we know she thought herself unsuited to) to do it

The students have themselves and future cohorts to protect, and commit to passing on QQ's teachings themselves to do it

And we'll make sure that Professor Quirrell's teachings never die out of Hogwarts.

Thus, Harry’s original christmas wish is at least partially fulfilled, despite PQ’s objections:

"And Mr. Potter wishes for -"

There was a pause as Professor Quirrell looked at the parchment.

Then, without any change of expression on Professor Quirrell's face, the sheet of parchment burst into flames, and burned with a brief, intense fire that left only drifting black dust sprinkling down from his hand.

"Please confine yourself to the possible, Mr. Potter," said Professor Quirrell, sounding very dry indeed.

(chapter 34)

"So what did you wish the first time?" said Draco.


"It wasn't really all that interesting," Harry said with obviously artificial lightness. "Just, I wish Professor Quirrell would teach Battle Magic again next year."

(chapter 35)

So I've been thinking about the feasibility of cutting stuff with a thin wire. As the thickness of the wire goes to zero, and the tensile strength goes correspondingly up, does the effort required for cutting actually go to zero?

It seems to me that it can't go to exactly zero, because you still need to counteract whatever forces were holding the material together. But does it go to a small value or a large value, in the case of cutting a strong material like bone? Say, if we tried using a thin wire to decapitate a person standing up, would they actually get decapitated, or would they just fall over?

Seems to me the force needed to penetrate tracks the diameter, but the strength tracks the area of the cross-section. That is, decrease the thickness by N and it decreases the force needed by N but the strength by N squared. Below a critical thickness, the wire would just break. Spiderwebs don't slice you up if you run into them.
There is nonzero finite surface energy involved in cleaving an object in two, which you need to impart (minimum applied force). But for a living thing the minimum would be low. And you can prevent falling over by using a circular wire that shrinks (or 2 or more wires arranged symmetrically) to counter any pushing non-cutting forces
How low are we talking?
The Wikipedia page on surface energy gives values in the hundreds to thousands of mJ/m^2 for solids. I haven't a clue where meat and bone would fall in that table, and I haven't been able to find out with five minutes of Google, but even if we assume they're on the high side we're not talking particularly high total energies. (Tangentially, "surface energy of meat" is one of the better phrases I've Googled lately.)

Since HP erased all or nearly all LV/QQ's memories, how is it different from actually killing him?

It doesn't activate his horcrux network.

Memories don't include skills. Voldemort still knows all of his spells.
It's a question I've wondered about myself. Obliviation makes a big difference in terms of the horcrux network, but I'm not sure what difference it makes in terms of Harry's reluctance to kill humans. If we assume that our future selves want all of us around because we're cute-- that is, delightful and harmless, will they want both Voldemort and Quirrell? Is it clear that Quirrell was Voldemort all the time? Would they want to give all our past selves (say, a sample of each of us from every major psychological change) to be given a chance to grow and develop? Will they be willing to kill each other in extreme circumstances because they won't be harmless relative to each other?
Thank you. Yes, my question was about the moral difference, not the technical one, as other replies seem to interpret it. I understand that Harry had to have precautions in case his transfiguration fails at some point, but still, he destroyed the identity of his mentor without an immediate need to do so. He could have delayed irreversible actions until he has time to reflect. Rather un-Harry-like at this point in the story. Unless I'm missing something.
Harry deleted (or tried to delete, we don't know he succeeded) LV/QQ's episodic memory, not his procedural memory (skills and spells). In principle, this could be fixed - in canon memory charms could sometimes be reversed, and in HPMOR most of LV's memories are backed up by the horcrux network. Sufficiently advanced magic might be able to extract those.
Unfortunately, deleting episodic memory while leaving procedural memory intact would mean that Voldemort would no longer remember the things he's able to do.
He might, however, learn his old skills a lot faster than he otherwise would have.
Addressed to everyone, not just AnthonyC: if your episodic memory were deleted and your procedural memory remained (and you could look at it from the outside), to what extent would you consider yourself to still exist?
Approximately the same extent to which I'd consider myself to exist in the event of any other form of information-theoretic death. Like, say, getting repeatedly shot in the head with a high powered rifle, or having my brain dissolved in acid.
Right. This is why I said that total obliviation is worse than death. Not only are you removed, you can later be used to support purposes outright opposed to your goals, as Harry intends to do with Voldemort.
This seems odd to me, though I'm not saying you're wrong. From the inside, my values seem far more akin to habits or reflexes than to time-indexed memories. I imagine Obliviated!me still having a NO DON'T reaction when asked to support a purpose opposed to my previous goals, because verbalised goals flow from wordless moral habits; not the other way around. (assuming a possibly inconsistent scenario where I retain enough language for someone to expect to manipulate me)
Since Voldemort's goal set was extremely self-centered, I'm not sure results in a universe where he no longer exists can be stated to opposed to his goals in any meaningful way. They simply don't concern him.
Quite a bit. I have a very bad memory for personal history anyway - I have a vague timeline of significant dates in my head, and a handful of random "vivid" memories, maybe one per year, that have been nailed down by neural happenstance. But if you asked me what I was doing yesterday evening, I think I would end up randomly selecting an evening from the last three or so - unless I painstakingly solved it in the manner of a logic puzzle ("I go to the gym on Wednesdays, and yesterday was Thursday, so I guess I was at the gym").
It's close to the same thing, yes. (Unless we count the horcrux backups, but since Harry doesn't mean for them to come into play, they don't count in this moral calculus.) I am okay with that.
An aside: a couple replies to you mention "horcrux backups", but that's Horcrux 1.0, the kind that Voldemort disdains for their failure to preserve continuity of identity. I get the impression that Horcrux 2.0 is more like RAID, but RAID is not backup. It's quite likely that now there are no backups and this was indeed a partial death.
Actually killing him (including his horcrux backup system, I assume?) would obliterate the LV-that-is and any possible LV-that-could-be. Harry obliterated the LV-that-is, but can still restore him to full health and allow him to become any one of the LV-that-could-be. It’s a bit like taking a life but starting a new life, too.

Guess no more plot. Nothing is happening.

My hope is slowly dying, that we'll get Dumbledore back and we'll get to see him finally, finally relieved that the threat that gave him so much grief is ended, and that the hero he believed in really did live up to his hopes.

I'm still holding out at least for Hermione to return as a Speaking Character.

There may be some hope yet; HPMOR has still got ~20,000 words left to go.
She's alive. I'd have to assume that she comes back. Kind of odd that she hasn't already. And have they told her parents yet? Harry really should have been apprising McGonagall of the truth, between Dumbledore being trapped, and Voldemort riding around on his finger. Maybe getting Dumbledore out is time dependent, being easier the closer to his capture. Who knows? I'd want people looking at it as soon as possible.

She's alive. I'd have to assume that she comes back. Kind of odd that she hasn't already. And have they told her parents yet?

Sad ending: when Hermione died, her parents wanted to complain to the Muggle authorities, so they Obliviated her parents of all memories of her.

Wizards would do that. In fact, Hermione did this herself to her parents in canon, although she preserved their memories first.
McGonagall's wording ("trapped outside Time") suggested to me that she knows at least the basics of where Dumbledore went. There can't be too many spells or artifacts capable of doing that, or Dumbledore wouldn't have had to resort to an Atlantean relic in the first place.

McGonagall's wording ("trapped outside Time") suggested to me that she knows at least the basics of where Dumbledore went.

She's just repeating what Harry said in Chapter 116:

"Dumbledore's gone!" cried Harry Potter. "The Headmaster is gone, Professor McGonagall! The Dark Lord trapped him, he reversed some kind of trap the Headmaster planned and Dumbledore was caught outside Time, he's gone!"

I can't imagine she'd just accept that without asking for some kind of clarification, or putting the pieces together herself -- I get the impression that the presence and general properties of the Mirror were common knowledge among faculty (what with everyone in Gryffindor having run the dungeon), though the details of Dumbledore's plan couldn't have been. But fair enough, I'd forgotten that bit.
Note that according to Dumbledore in Chapter 61, Atlantis itself was also "erased from Time" (paraphrasing here). Coincidence?

So Dumbledore is not trapped but simply takes a well-deserved vacation in Atlantis!

The mirror is likely also the tool that erased Atlantis from time.
I wonder if Dumbledore briefed her on the trap.

My guess would be no. Generally speaking it's a good idea to let someone else in on a scheme like that, so that you have someone to scrape you out when things go horribly wrong; but wizarding culture seems a lot more secretive and heavy on information control than ours, which indeed may not be such a bad idea in context. You can't Legilemens something that someone doesn't know.

So, QQ was Ravenclaw and David Munroe was Slytherin (?)... Both facts are public record. Yet QQ is celebrated as "the best Slytherin that ever was".

Someone is bound to ask questions.

Isn't the official story telling that David Munroe usurped Quirell identity in order to teach Defense at Hogwart?

QQ can't be polyjuced, which seemed to be the Auror's earlier assumption, because it would have worn off now he's dead. So given that David Munroe looks different from Quirell, the obvious next hypothosis is that he is a Metamorphmagus. But still, that is extremely rare, which is suspicious. But next, surely some people who knew the real Quirrel are going to turn up to his funeral, and start asking questions like "what do you mean he's a Slitherine?"

If such people existed, they might have shown up during the school year, when it was publicized that QQ was teaching at Hogwarts. Voldemort may have removed them before he started teaching.
People often turn up to funerals even if they haven't seen the deceased for a decade or more, all the more so if the deceased died fighting a dark lord. Plus, this is going to make the news in a way that the appointment of a new defense professor would not.
The Officials involved have believed Quirrel to be David Monroe for a long time (chapter 84), that seems to have become the Official Story over the last couple days, and Mad-Eye Moody knew that Quirrelmort should have been fired out of a cannon into a sun as soon as he took the Defense position, so they've been asking questions and taking the first reasonable answer for a while. I'm fully expected Moody to dive through a door with stunners flying, yelling "Not paranoid enough!" because /someone/ didn't expect door transfiguration, but most of the other people involved have already gotten suspicious and had their suspicions allayed.

On Harry's left hand, a tiny emerald glowed bright beneath the morning sun.

He's wearing Voldemort's Transfigured form on his hand? Wouldn't another toe ring like the one he used for Hermione be more secure?

The fact that he's wearing it at all stuns me. It needs to be maintained by a coven of the greatest wizards around.

Imagine: Harry dies (heart attack, stroke, stabbed by Goyle, whatever) Handless amnesiac Voldemort appears, dies of human transfiguration sickness after a few deeply confused minutes Horcrux network activates.
Best case, this amnesiac being can't figure out how to possess anyone. Medium case, somebody gets possessed by the clueless shade.
Worst case: network was built to supplement current memories with dump of previous ones (we can see by the part where Voldemort Confounds himself before the Mirror that he had thought about the concept of changing his mental state), and the Dark Lord is back in business

we can see by the part where Voldemort Confounds himself before the Mirror that he had thought about the concept of changing his mental state

Note that it was Harry, not Voldemort, who came up with that idea. (Chapter 109) So, no, Voldemort most likely did not think of that.

The fact that he's wearing it at all stuns me. It needs to be maintained by a coven of the greatest wizards around.


But Harry tends not to see other people as PCs, or as able to add anything to his plots.

Kind of an interesting mirror to Voldemort, yes? The one Tom has trouble thinking of ideas that involve him being helpful to other people; the other has trouble thinking of ideas that involve other people being helpful to him.

The fact that he's wearing it at all stuns me. It needs to be maintained by a coven of the greatest wizards around.

An excellent point. Harry could catch some disease that leaves him bedridden and incoherent for a few days. Or one of his experiments with magic could end with him waking up in the hospital the next day. He's taking an extreme risk here.

Still, this isn't out of character for HPMOR Harry. His inexperience and reluctance to confer with older wizards went a long way to helping Voldemort return.

Oh yeah, its definitely in character, and, also, to be fair, he's a traumatized child and its only been a little while. I'm sure he'll find a way to keep it safe once his mind kicks back into gear.

Agreed, and add to all of those risks that Harry is an obliviation noob and he may not have gotten the wipe right. We don't know what Voldemort will or will not remember if he wakes. Even in the medium case of possession by an amnesiac, V might figure out who he probably is, or get briefed by a servant who figures it out. The list of recently deceased epically powered wizards in the world is pretty short. And Harry is being naive again: The issue with psychopathy is not that these people are not happy, but that they are not capable of empathy. Not that it needs to be taught, but that the brain circuitry for empathy is not functional. Being raised in a kind versus abusive environment matters, but the difference that produces is between someone who is merely cold, selfish, manipulative, and calculating versus someone who is all of those things in a serial killer kind of way. Muggles have no therapy for it. Maybe magic does, but it isn't a question of teaching Quirrell to be happy. Quirrell will have to be changed into a person who is a capable of genuinely caring about people who are not him.
Brains are flexible, so why can't psychopaths learn empathy using different circuitry? If sufficiently motivated, that is.
It's not nearly that simple. In a nutshell, their brains are very noticeably different from normal brains, the track record of treatment has been not only ineffective but sometimes counterproductive, and the problem is considered by many to be intractable. The studies done were not done well, and there have been some promising results with "decompression treatment" for juveniles who are mild to moderate in their psychopathy, and no other group. It would be a great boon to society if adult psychopaths could be rehabilitated, but no one knows how to do it. I encourage you to peruse the whole thing if you have time, but here are some excerpts:
Thanks, that's very interesting.
Watching Charlie Rose this weekend, they briefly discussed recent findings on brain scans of psychopaths. Shriveled amygdalas so they felt little fear, but amped up goal pursuit system (sorry, can't remember the brain area).
If Harry would give it to Moody and Bones, they would very likely go through with the mirror plan and remove Voldemort from time. Harry seems to hope that he can later recover part of Voldemort's magic.
That does seem the best long term disposal. Preserves his current state indefinitely.
Meh: It's been like a day and there are tons of steps Harry need to take longterm. He might even have started taking these steps offscreen.
What would happen if he used the Philosopher's Stone on Voldemort's transfigured form? I guess the transfiguration would become irreversible. He wants to figure out how to restore Quirrel, but is the risk of accidentally releasing Voldemort worth it?
People have speculated that making the transfiguration permanent would risk activating the Horcrux network.
I wondered the same thing, But couldn't he also later use the stone to reverse it by re-transfiguring it to Voldemort's body?
You can't transfigure (via free transfiguration) anything into a target you don't understand completely. Otherwise it will be just an imitation.

I like this chapter quite a bit. I believe that, while consciousness is an important part of oneself, one's legacy also matters, and in this case, the good work Quirrell did is part of him.

A part surely overwhelmed by the legacy he left behind as Voldemort, which includes lots of orphans and lots of people whose own positive legacies he cut short by killing them. If you're going to count legacy as part of one's self, then anyone who kills people for any reason is going to end up in the karmic negative very very quickly, because they are taking away other people's legacies, and their potential children's, and their potential children's, etc.
The absence of those future people in the world means more resources for other future people. If the population is at equilibrium, the effect on getting rid of the legacies of the people you killed is exactly balanced out by the increase in the legacies of other people who now have the resources to exist and are using them instead. (If the population is growing, or if the population is in a steady state that is not an equilibrium because when it is pushed to one side it stays that way, then killing someone can take away legacies as you suggest. But you can't then conclude that this is bad unless you also want to accept that it is good to add people, which leads you to the repugnant conclusion.)

WTF was Harry forgetting when he grabbed the Remembrall?

That he is Tom Riddle. A whole lifetime's worth of stuff, which is repressed and forgotten by Tom Riddle Jr.

I hope Voldemort's "fallback weapon" also had sunlight-resistant skin. Otherwise Hermione might have issues with going outside...

I also take it that Harry's refusal to give Quirrell's eulogy even before he knew Q = V is because of his views on death in general.

Speaking of the eulogy, is Harry cheering at the end? And does he have any way of protecting his Transfigurations against Finite Incantatem?

The Stone would make his transfiguration permanent and thus presumably render them immune to Finite Incantatem. If he doesn’t use the Stone (e.g. in the case of Voldemort, which you are probably referring to), I don’t know of any conventional way to proof against F.I. (Knowing Harry, I’m sure he’d be able to think of some rather unconventional ideas if he sets his mind on it.)

I guess I'm still confused by something, hopefully someone can explain it to me...

I believe Voldemort stated he had some sort of fail-safe set up to kill the students at the Quidditch game if he did not get the Stone of Permanence. Was it ever explained how the fail-safe was dismantled?

It was briefly noted in chapter 111:

... ... ... someone else at the school knows that Quirrel was doing something weird, and called him lord.

Mind magic, or their own will? Obliviation, but was the entire inception of that loyalty during that six hours or does she remember anything?

Some usage of the Imperius curse seems most likely to me. Or a Death Eaters using polyjuice. There are so many ways for LV to manage such things that it doesn't really matter how exactly he did it. ;)
Thanks, not sure how I missed that.
He told another student to disarm it. He didn't need the stone to undo it.