I’d like to withdraw a theory in my OP, specifically the identity of the half-blood prince. I came across another theory today that fits all the facts so well, that I have to consider it a book 6 spoiler, and I am thus boxing it:
[spoiler]We know the following information about the book, right from Rowling herself: It’s called “The Half-Blood Prince;” we’ll hear more about Voldemort’s past, the Prince is not Harry or Voldemort, Chamber of Secrets was originally entitled, “The Half-Blood Prince,” and there is still a clue or clues in that book
Now, most people saw, “It won’t be Voldemort,” and read, “It won’t be Tom Riddle.” Bad mistake, this theory goes, particularly when you consider this pair of quotes from Chamber of Secrets:
“Harry: ‘Hang on – this hasn’t got anything to do with Vol – with You Know Who, has it? You could just shake or nod…’
Slowly, Dobby shook his head.
‘Not – not *He who Must Not Be Named, sir.’” (p. 18, British paperback edit)
Then later on,
“‘I’ve just got one question, Dobby,’ said Harry, as Dobby pulled on Harry’s sock with shaking hands. ‘You told me this had nothing to do with He Who Must Not Be Named, remember? Well–’
‘It was a clue, sir,’ said Dobby…‘Dobby was giving you a clue…’” (p.249)
Yes, indeed. And what else qualifies in this series as being a prince, if it’s not being The Heir of Slytherin? And isn’t Tom Riddle the very first character in the series to be refered to as a half-blood?[/spoiler]