Harry Potter question...

I've been wondering about the Sorting process. Specifically I've been wondering about the requisites for being sorted in the Slytherin house. Until OotP sorting seemed to be just based on character traits, the emphasis was definitely on the student's qualities. However that changed with the fifth book, at least if the Sorting Hat Song is credible. While Ravenclaw, and Gryffindor were still more or less characterized by the same criteria (that is the brave, bold, daring etc for Gryffindor, the most intelligent for Ravenclaw), Hufflepuff's founder was basically characterized as having no special character requirements, since she'd teach "the rest" when previously Hufflepuffs were characterized as just, loyal, true, patient, hard-workers etc. and the most drastic shift of emphasis was in the Slytherin description, where cunning was still mentioned, but the focus was on "pure ancestry" which the Hat never mentioned in the two other songs, IIRC. In them it was cunning, ambition, and ends over means approach, hunger for power that distinguished the Slytherin house.

I can sort of reconcile the original intentions of the Hufflepuff founder, as described by the Hat, with what the later Hufflepuff characteristics, as described by the Hat, are. However, according to the Hat in OotP, Salazar Slytherin intended his house to be "pure-blood" only. Yet we also know that the Hat does not sort only pure-blood wizards into Slytherin: Tom Riddle/Voldemort had a Muggle father after all, and it considered Harry for Slytherin, who, though not Muggle-born himself, had a Muggle-born mother, which I doubt Salazar Slytherin would have considered "purest ancestry," so the Hat doesn't seem too concerned about Salazar Slytherin's "pure-blood" agenda when considering potential candidates. And I don't see how it could be, after all since Hogwarts admits Muggle-born students, there have to be those among them who are cunning and ambitious etc and generally fit best with Slytherin, it certainly would be a problem, if in the current set-up they would be sorted into Hufflepuff, because the Hufflepuff founder intended once to accept "the rest" (as they might have been way back around Salazar Slytherin's and Helga Hufflepuff's time). Yet it can't be easy for Muggle-born Slytherins, considering the history and the founder of their house and some of its current members.

So what are the opinions on this problem? Are Muggle-born Slytherins very rare exceptions (I don't remember any besides Tom Riddle), and generally only pure-blood students are sorted into Slytherin? How much is the Sorting Hat bound by the initial founders, who created it for sorting, and their intentions for their respective houses anyway?

Now, as a caveat, I've only read the books once, and I'm not involved in the fandom or on any discussion lists, so this may be a well-trodden area for HP fans -- in that case maybe someone could point me into the direction of essays or previous discussion about this -- or I might have missed/forgotten/overlooked some further explanation in the books. But I'm interested in theories about how this works.

finally...

Since this afternoon I've been looking for a word, not continuously, but the word's absence has been nagging at me. I just couldn't recall it. It has been very frustrating. The only word that would come to my mind was a colloquialism, an expression that roughly means the same, but in a broader sense, and I certainly couldn't write that one down in the context I wanted to use the word. I've never heard or seen it anywhere but in an informal context, and quite frankly it looks rather ridiculous when you write it down, but what I was looking for -- that much I knew -- was a foreign word, something with Greek or Latin roots.

I wanted an adjective describing expressions that have two parts/words saying the same thing, one of which would be redundant or used for rhetorical emphasis, i.e. I was looking for "tautologisch" (tautological in English). But for the life of me I couldn't remember that frelling word. All I could think was "that foreign word you can use for 'doppelt gemoppelt' when you're talking about rhetoric and word choice."

Eventually it occurred to me that English certainly would use the same foreign word, and it might just turn up when I put "doppelt gemoppelt" in an online dictionary. And indeed it did. I could have saved myself some annoyance, if I had had this simple idea earlier, not to mention that instead of tossing and turning I might have fallen asleep at a reasonable hour instead of thinking about Harry Potter questions and turning on the computer again to distract myself (see the previous entry). At least when I saw the translation I had a moment of fun when I imagined some hapless person using the rather highbrow "tautological" for some of the more everyday examples of "doppelt gemoppelt" as (strangely) "tautological" is the only translation given.