My theory is that potions which don't involve magical ingredients are obscure because they're usually less powerful and because they require a greater investment of energy from the creator to do the reshaping (explaining why Harry doesn't do very much in that battle). Given that Flitwick and McGonagal had suggestions of books to make at all after hearing what Harry wanted, it seems very likely that such potions do exist, just not in the standard textbooks. It seems very likely that Harry got his potion out of a book, because potions research is dangerous and presumably very time consuming, and because Harry with the ability to invent potions would be powerful enough to wreck the story.
Harry with the ability to invent potions would be powerful enough to wreck the story.
Harry with time travel would be enough to wreak the story. Harry with an invisibility cloak would be enough to wreak the story, Hell, harry with rationality would be enough to wreak the story.
That is, unless the other obstacles were ramped up to deal with it. Give Harry a time turner and enemies clever enough to know how to check on him. Give harry an invisibility cloak but add spells that can detect the presence of a deathly hallow. Give Harry mastery of potions but make creating them slow or just plain difficult.
(The HPMOR discussion thread after this one is here.)
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. There haven't been any chapters recently, but it looks like there are a bunch in the pipeline and the old thread is nearing 700 comments. The latest chapter as of 7th March 2012 is Ch. 77.
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.
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: one, two, three, four, five, six, seven, eight, nine.
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: