I have always been confused on the whole "Pure-Blood" issue and HBP didn't help.
Various points (paraphrased cause I don't have my books):
In SS, at the robes shop, Draco asks Harry if he is "the right sort." Harry replies that his parents were a witch and a wizard. This appears to be acceptable to Draco. Conclusion: a child of muggleborn magic-users would be considered "pure."
In CoS, some guy, who's name escapes me, announces that he is pure-blooded back seven generations. He apparently is attempting to defend himself. Conclusion: more is better, though that doesn't go against the conclusion of the first book.
Don't recall anything particularly from PoA.
In GoF we discover it is acceptable to interbreed with non-human magical creatures, though some (veelas) are better than others (giants). The offspring is still pure.
In OotP, they discuss how inter-bred the group of "pure" families is. Most everyone is second or third cousin to everyone else. This doesn't seem sensible to me.
In HBP, we see how stupid overbreeding is: the Gaunt family has continuously married first cousins. There is not enough genetic material left to scrape together a full person (as Eddie Izzard would put it). This can't have gone unnoticed by the magical community.
Also in HBP, Hermione says something to the effect that "There are no pure bloods." This tends to go against the conclusion of the first book, since it implies there is some number of generations one must have without muggles.
So how pure is pure? Where is the cut-off?
I think those that are completely muggle born are the ones that are suspect. If Hermione and Ron marry, their kids would be considered pure blood. My guess is that other familes (without the Slytherin insanity) have intermingled with Muggle-borns to some degree (how else could there be so many Muggle-borns with magic?), but they aren't discussed in polite pure bred society.
I read the whole pure-blood family tree thing sort of like royalty. The Blacks simply ignored half-bloods or Muggles so that they could SAY they were pure.
As for Draco and Harry's first encounter, Draco didn't ask about Harry's grandparents. He's been brought up as a pureblood, but at the age of eleven, it might not have occurred to him that one of Harry's parents might have been Muggle-born.
And I didn't think half-breeds were considered pure by either side. Madame Maxime goes to great lengths to hide her giant blood, remember, and Hagrid doesn't exactly go around announcing his heritage.
I think the idea is based largely around nobility (you'll recall that numerous lines of the British and other European nobility literally died out because they simply inbred themselves to death, think of George II). If both of your parents are wizards, you're pure-blood, but you may not be one of the old wizarding families. When Hermione says there are no full-bloods left, I think she means that none of the wizarding families could have lived this long without occasional new blood from muggle-borns.
When Hermione says there are no full-bloods left, I think she means that none of the wizarding families could have lived this long without occasional new blood from muggle-borns.
I agree. As we've seen with the Black family those who didn't 'keep it in the family' were blasted off the tapestry and ignored. It's possible that many 'pureblood' famlies have the same attitude meaning they may have muggel blood but they're not going to tell you about it.
In GoF we discover it is acceptable to interbreed with non-human magical creatures, though some (veelas) are better than others (giants).
That's a good point, but I have to wonder--is it widely-known that Fleur has veela blood? I guess I was under the impression that the only reason anyone found out was because she admitted that the magical core of her wand was a hair from her grandmother, so those present at the wand-weighing would've put two and two together. I guess I didn't think it was common knowledge.
Even so, it's pretty easy to accept that the child of a human and a veela would garner more acceptance in the world at large than the child of a giant and a human, simply because veelas are not nearly as intimidating and/or frightening as giants (depending on who you are, of course ^^).
If I could find a good picture of the Gaunt family near the very end of their line, I'd love an icon with the phrase, "Because it's a bad idea when cousins marry!" :P
As for the 'blood' question, that's something that I've been curious about, too. I guess I find it hard to believe that as long as there is one degree of separation between Muggle and magical folk, it's okay. Another thing that I find is interesting is that while spontaneous generation of magic powers in children of non-magical parents is scoffed at, the child of a Muggle and a witch/wizard is not. I'd think that a half-blood would get as much flak as a non-blood, when you consider the vitriol directed toward the latter.