An AI researcher called Eliezer Yudkowsky is writing a Harry Potter fanfic called “Harry Potter and the Methods of Rationality“. The summary of the summary: it’s really good, and I’m not one to usually recommend fan fiction.
Petunia married an Oxford professor, who raised Harry as his own son, and taught him about the importance of science. Harry is a Bayesian rationalist, and he employs that art, as well as the scientific method, in Hogwarts.
It took me, to my shame, quite some time to understand why this is not “single point of departure”: there are other changes which are not implied by this change alone. But all changes are implied by this change and one other rule, that the author quotes:
The First Law of Fanfiction states that every change which strengthens the protagonists requires a corresponding worsening of their challenges. Or in plainer language: You can’t make Frodo a Jedi without giving Sauron the Death Star.
It is hard to understand exactly how much making Harry Potter into a rationalist is like making Frodo a Jedi. Canon!Potter is, well, a moron. For example: here is how the plot of “Philosopher’s Stone” would have gone if Harry was not a moron:
Harry learned that the 3rd floor corridor is off-limits to students, and so kept out of it. When he suspected Professor Snape tried to break in, he immediately informed Dumbledor and McGonagall. When Professor Quirrel tried to steal the stone, he easily went through the first three wards, but the last stumped him. He saw himself in the mirror using the stone, but this did not give him any clue regarding its location. As he sat and puzzled, the owl that Harry sent reached Dumbledor, who apparated just outside Hogwarts, Accioed his broom, and flew in, and saw Quirrel trying to steal the stone. Soon, Quirrel was hauled off to Azkaban, Dumledor having summoned several Aurors to take him away.
If you make Harry into not merely a non-moron, but an actual Bayesian-optimization-junky, you have to give You-Know-Who the equivalent of the death star to stop MoR!Harry from revolutionizing magic while You-Know-Who languishes away. So, yes, MoR is not “single point of departure”, it’s “parallel universe” or “alternate universe”. But if you were continually frustrated with how utterly stupid all the characters in HP are, the author does a wonderful job of fixing all the idiocies and the plot-holes.
(Oh, also: It’s a vector for infecting your mind with rationality. Just FYI.)