The premise of "Potter and the Methods of Rationality" is what would have happened if aunt Petunia married a scientist instead, and Harry was raised in such an environment?

Is this the only difference at the branching point of the two stories (the original and the fan-fic)?

It seems, at first glance, that everything happens as it did in the original Harry Potter universe, and everyone has the same personality as in the original, until Harry arrives and the butterfly effect kicks in.

However, this does not explain why Professor Quirrel, Dumbledore and Voldemort have vastly different personalities/behavior compared to the original.

I could understand Dumbledore, as he might have been observing Harry before he turned 11, and acts accordingly.

But why does Voldemort in this universe differ so much from the original one even before really interacting with Harry??

Are there other differences between the two universes besides the husband of aunt Petunia, or it's just Harrys scar/connection having an effect on Voldemort?

  • 1
    Tom Riddle, in the original novels, is shown to be quite insane because creating a horcrux splits the soul according to JKR. But in HPMOR, Voldemort has diamond-clarity intelligence, even after creating more than 100 horcruxes. Tom Riddle is just not worthy to be called 'Voldemort' in the original novels.
    – user88577
    Commented Aug 19, 2017 at 8:15
  • To my mind, the single point of departure is that the characters are at least level-1 intelligent characters (the minimal intelligence of an ordinary person outside of fiction) as described at yudkowsky.tumblr.com/writing. Harry and Quirrell are of course more intelligent than that (as are many other characters), but that is the minimum, and it's more intelligent than a lot of fictional characters (in and out of Harry Potter). Commented Jul 9, 2018 at 10:13
  • 1
    There's also a great thing that I can't find now, where Yudkowsky explains that HPMOR (unlike HP canon) is NOT children's literature and as such just can't have flat-out ridiculous things like Peter Pettigrew hiding out with the Weasleys for 12 years. (He put in the bit about Bill Weasley in HPMOR specifically to dispose of that example.) All part of an essay where he claims that writing children's literature is too hard for him, so he had to write something that makes more sense instead. Commented Jul 9, 2018 at 10:16

5 Answers 5


In the first chapter it says:

This is not a strict single-point-of-departure fic - there exists a primary point of departure, at some point in the past, but also other alterations. The best term I've heard for this fic is "parallel universe".

The text contains many clues...

From the mysterious phrasing here, not to mention the following paragraph, it seems like the primary point of departure is unknown, and one of the puzzles of the story is to work it out.


Yes, there are a considerable number of different 'background events' that are different, but I'm hesitant to list them all as they are spoilers for anyone who hasn't spotted them yet. (Specifically, the kind that give you a satisfying 'Ah ha!' moment.. I really hate stealing those from people :) )

One obvious one, however, is Voldemort, and his method of applying the Horcrux concept.

Voldemort made the Pioneer plaque a Horcrux. Good luck reaching THAT and destroying it.

This world has characters whose back-stories have them acting in what the author considers to be a much more 'sane' manner, and even Voldy (or an unresolved possibly Voldy stand-in) is rather genre-savvy, going so far as to quote the 'Evil-Overlord list.'

Also, more significantly, the nature of 'Good' and 'Evil' characters is far more questionable, including their deeds in the past. Many 'Good' ones have done things that the Canon HP version would never have done, and the Evil ones (at least some of them) may not be quite as evil as they are perceived. (Bellaxtrix Lestrange being a simple, but effective example. Her motives are not what they were in Canon HP.)

One way to think of the HPMOR stories is this: The same cast, but, for the Major Characters, starting at each of their births, acting more 'rationally' by the definitions the author uses. Many places things are the same.. But not all, by a long shot.

  • The question is not about the "different background events" per se, but whether there are different background event which are completely independent from the differences between the old and new Harry. A lot of characters start exactly as they were in the original, and start developing differently because of Harry. The only exceptions I found were Dumbledore (who might have observed Harry before) and Voldemort (who might be affected by their "connection")... However, you might be right about Bellatrix, I will rethink it after reaching the chapters featuring her more.
    – vsz
    Commented Apr 16, 2013 at 6:07
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    Well, keep reading.. :) As you farther into the story, there are a lot more back-story difference, involving people who have never met Harry, yet lived very different lives from how JKR had them live. It's much harder to see, early on, as the author was giving us a 'familiar setting' to work from, but even the magic that is taught shows some fundamental differences that pre-date Harry. (Transfiguration, for example, is MASSIVELY different.)
    – K-H-W
    Commented Apr 16, 2013 at 13:47

Yes, the universe of "Harry Potter and the Methods of Rationality" is not an alternate history branching off at a certain point, and differs not just in the behaviour of characters: it works differently than the one of J.K. Rowling.

Basically, it represents the author's attempt to fix things where (in his view) Rowling's story and world are illogical, inconsistent or the consequences of things not sufficiently thought-out (And I consider the willingness to go to such lengths in this a great compliment towards Rowling's truly amazing world-building).

In some cases, such flaws are merely pointed out, usually by Harry (whose different upbringing allows the author to use Harry more like an avatar than a Mary Sue):

  • Quidditch scoring (which is just bad game design and should lead to tactics that are rather different than what we are shown).
  • Wizarding currency and the unused arbitrage opportunities it represents.

In others, the consequences of plot points are explored in some detail and cause actual differences in the story:

  • As K-H-W mentions in a comment, Transfiguration is logically way more dangerous than described by Rowling, which is explained in detail, and

    Harry uses it as a deadly weapon

  • The nature of Azkaban should be considered too horrifying, deadly and inhumane to be tolerated by modern wizards; MoR shows this

    through its portrayal of Bellatrix, who is consequently a very different character, at least in chapters she appears in so far

  • 2
    “And I consider the willingness to go to such lengths in this a great compliment towards Rowling's truly amazing world-building” — There’s not really any good reason to think this. For instance, it could be a compliment towards her good storytelling instead. Case in point: the worldbuilding in Harry Potter is mediocre or worse in many aspects (and some of the problems are highlighted in HPMOR). Rather, it’s the excellent storytelling that makes Harry Potter so special. Commented Jan 29, 2016 at 16:50

In the presence of new chapters, I think this question deserves a new answer. Unfortunately, there's little that can be said without spoiling. You are incorrect in assuming that Petunia marrying a professor is the greatest point of departure; while it is certainly one of the points, the following is a far greater one:

Voldemort is (and always was) far smarter than he is in canon. When he came to the Potters, he had different intentions, and the result of that night was also rather different. The difference in Harry's personality is as much a consequence of that as it is of him being brought up by different people.

If you want to figure it out for yourself, I advise supposing for a moment that Eliezer Yudkowski is a perfect writer. If you get the feeling something sounds wrong, don't blame it on bad writing; instead try to come up with a world in which it sounds right.

  • I want to know a lot more... What is the primary point of departure? I've tried to trace it back through the timelines and it gets really muddy when you consider the centuries long backstory the author puts on certain artifacts. I've also not been able to puzzle out where the author is saying "This is definitely different from what JKR wrote" and "This is a perfectly logical explanation for events JKR wrote".
    – Dacio
    Commented Jan 10, 2018 at 20:50

No, the changes from canon are too great for the single event of who Aunt Petunia married to have reasonably caused.

I believe the premise behind MoR is to show how people would really react to magic outside of fiction, and what they would try to use it for (provided everyone is also super genius Batman who plans out moves years in advance and lies constantly).

EDIT: To clarify, any changes to character personalities come from the idea of "how would people actually act in this magical world?" instead of any specific in-universe events.

  • 3
    I'm not familiar with the work in question (MoR), but I'm not sure if you're distinguishing between 'branching points' and 'actual differences'. I think the OP is talking about events prior to the beginning of either HP or MoR.
    – AncientSwordRage
    Commented Apr 15, 2013 at 22:18
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    +1 just for "everyone is also super genius Batman who plans out moves years in advance and lies constantly". The Harry in MoR would be such a Mary Sue it wouldn't even be funny, except Every. Other. Character is also a Mary Sue.
    – Martha
    Commented Apr 15, 2013 at 23:18
  • 2
    Heh, not to mention that Harry in canon is a Sue-a-saurus Rex. I love him, but he does register quite easily on the Sueometer. Commented Apr 15, 2013 at 23:48
  • "the changes from canon are too great ..." , yes, but if they are caused by interacting with a different Harry, than there is still only one difference at the branching point. I'm looking for differences which might not be caused (solely) by a different Harry.
    – vsz
    Commented Apr 16, 2013 at 4:32

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