I suppose "elementary" in the sense of "fundamental" or "simple" or "not relying on other skills before you can learn it", rather than in the sense of "easy" or "widespread".
Contrast literacy. Being to read and write one's own language is elementary. It can be grasped by a small child, and has no prerequisites other than vision, reasonable motor control and not having certain specific brain dysfunctions. Yet one does not have to cast one's mind that far back through history to reach the days in which this skill was reserved for an educated minority, and most people managed to live their whole lives without picking it up.
New chapter!
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 102.
There is 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.)
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: