As far as Christmas and Easter goes, the first of these specifically has a non-religious explanation in HPMoR:
The atmosphere at Hogwarts before Yuletide was usually bright and cheerful. The Great Hall had already been decorated in green and red, after a Slytherin and a Gryffindor whose Yule wedding had become a symbol of friendship transcending Houses and allegiances, a tradition almost as ancient as Hogwarts itself and which had even spread to Muggle countries.
No similar explanation has been given for Easter, but I think it's reasonable to suppose that one exists.
I took that passage to indicate the tradition of green and red colors during Christmastide, not of the origination of any holiday,
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 96. The previous thread is at almost 300 comments.
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, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, .
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