This post is a continuation of a discussion in the comboxes on Darwin's earlier Harry Potter post.
It seems to me that two discussions are going on at the same time: the question of the validity of Rowling's post-series revelation that Dumbledore is gay (as in, he once had a crush on a guy); and the issue of positivism as it relates to a text. The two may or may not be related.
First, what exactly is positivism? Commenter Zippy used the term in his first reponse:
"But the idea that Dumbledore's gayness is only pertinent if it can be verified in the canonical text (using some unspecified verification procedure) is a form of positivism; and you probably know what I think of positivism. Sola the canonical text doesn't work any better as a theory of meaning in literature than it does as a theory of meaning in theology." When I asked for a further clarification of positivism, he replied: "For the purposes of this discussion, by "positivist" I mean someone who believes that a text taken alone is meaningful."
Wikipedia tells me that "Positivism is a philosophy that states that the only authentic knowledge is scientific knowledge, and that such knowledge can only come from positive affirmation of theories through strict scientific method." The American Dictionary of Cultural Heritage defines positivism thusly: "An approach to philosophy frequently found in the twentieth century. Positivists usually hold that all meaningful statements must be either logical inferences or sense descriptions, and they usually argue that the statements found in metaphysics, such as “Human beings are free” or “Human beings are not free,” are meaningless because they cannot possibly be verified by the senses."
Now perhaps there is a theory of literary positivism not covered by my above sources, but I wonder if positivism can be applied to a work of fiction. Since the writing of fiction is an act of sub-creation (in that the author is [or ought to be] constructing a fictive world in which his characters and plot advance) it's incumbent on the author to develop his narrative in such as way that it's coherent enough to be understood in and of itself, and then allow it stand on its own. The story ceases to exist simply in the mind of the author and begins to exist in the mind of the reader as well, and the reader, before grappling with appendices, post-scripts or revisions, must first grapple with the book that is presented to him.
In The Mind of the Maker, Dorothy Sayers says that "For the reader, that is, the book itself is presented as a three-fold being": the book as Thought (that is, the book in the mind of the author); the book as Written; and the book as Read. The author is of course free to later expostulate on the ideas and motivations and sources that induced him to write the characters as he did, but the fact remains that the reader encounters what the author has chosen to write.
So positivism doesn't really seem to be a useful description of the kind of criticism that involves by comparing a statement about the book (even if made by the author) with the book itself and saying, "Eh, not so much." The text has to be jumping-off point for discussion, or else there's nothing to discuss. Perhaps a better comparison is that the text is magisterial, and that authorial press conferences are like private revelations?
Now as to Potter. The issue with Rowling's outing of Dumbledore (as I see it) is that it is indeed a revelation: the story that she created and published bears no reference to homosexuality. The events that would seem to justify her revelation -- a young man gets excited by the ideas of another young man, and is led into endorsing some Bad Ideas -- are more convincingly and satisfyingly explained by the motivation contained within the work itself: pride. "But I loved him!" is less interesting from the point of character development than "I'm better than all you fools, and the fact that this charismatic figure here agrees with me is proof!" If, as she was writing the novel (for given her plot innovations with each successive novel, it's improbable that she came up with the "gay" idea before she wrote book 7) she suddenly realized that Dumbledore was inclined to man-love, she was careful to put no hint of it into the book itself.
In that case, it becomes gnostic knowledge, unknowable except to the fans who will remember this press conference after it fades from public memory (say, next year). But frankly, evaluating literature in terms of gnosticism or positivism seems to stretch those terms far enough past their definitions that they just become jargon to sling around.