Harry Potter and the Methods of Rationality discussion thread, part 14, chapter 82

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The new discussion thread (part 15) is here.

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 82. The previous thread passed 1000 comments as of the time of this writing, and so has long passed 500. Comment in the 13th thread until you read chapter 82.

There is now a site dedicated to the story at hpmor.com, 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 hpmor.com.)

The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13.

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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Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).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.

The new discussion thread (part 15) is here.

As a reminder, it’s often useful to start your comment by indicating which chapter you are commenting 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Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).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.

you should also consider the amount of cases where people said the same "he's kind of a weirdo", but that person did not go on to do something horrible. And also the amount of cases where people did not say it, and yet the person did something horrible. All three are necessary to calculating the strength of the evidence "people say he's kind of a weirdo" in favor of the hypothesis "he will do something horrible"

Well, yeah, I agree, but I wasn’t trying to do that. At least I don’t think I was, and if it’s an implied assumption in what I said I don’t see it.

My original comment just said that I suspect many of the “I had no suspicion” after-crime statements are false (consciously or not), and was based mostly on how I suspect people’s brains might react, not on the rates of horrible acts.

My second comment I think said the same thing your quote above does, except adding that I also suspect a certain ordering of rates. But as I said in my first comment, I don’t have the actual rates and I believe they’re hard to obtain, so it’s just a suspicion.

After all, I don't expect a random stranger on the street to suddenly commit a horrible deed; why should I expect it more of an acquaintance unless there are concrete warning signs, which would make me say "I always knew he was up to no good".

The true opposite of "I always knew..." would on this view be like Harry's reaction to Hermione confessing attempted murder: "I don't believe she did it, it's a priori so improbable there must be another explanation or very special circumstances".

That’s true. I guess there are just very few people with this kind of reasoning (à la the Wizengamot); once they heard it happened, most probably take it for granted it was so, and they have only the “knew it all the time”/“didn’t see it coming” alternatives.

After all, I don't expect a random stranger on the street to suddenly commit a horrible deed; why should I expect it more of an acquaintance unless there are concrete warning signs, which would make me say "I always knew he was up to no good".

For a random stranger you have only the base rate to go on, you’ve got no other evidence. (Though for specific strangers you might have stuff like “he looks like a mobster” or “I’m in a dangerous neighborhood”, or maybe “he’s black and wears a hoodie”, which are a bit different as signs go.)

My claim is not quite that “weird people murder more often”. Instead, I suspect that “of the people who murder, a big majority were not stable/calm enough before and did give signs before”, and many if not most of the cases of people claiming there were no signs are because they just forget or ignore those signs.

(The two sentences are different if it so happens that there are very few people that give no signs, enough so that the fraction of them who do horrible things is less than the fraction of those who did give signs. Which I believe unlikely but not quite impossible.)