Likewise, I'm sure.
Yes, it is. Or it can be. Words often have more than one meaning, but you're aggressively ignoring any except one narrow use, in your narrow context. And the fact that you're refusing to admit that doesn't change the truth of it.
Only authorities determine canon - we agree on that. In this case, the Authority is Atlas and their editorial staff. And that staff allows writers to create canon - we agree on that. They edit it, but the canon comes through that process. Cool.
Then who is it for?
Because "canon" is meaningless until its applied. It cannot exist in a vacuum, since "correct" is meaningless unless "incorrect" is a possibility. In religion, "canon" is doctrinal interpretation and world view, as practiced and understood by priests and the faithful. A priest does not create canon, but he does practice and preach canon. So altho' religious canon is not affected by the masses, canon does exist in and through those masses.
And that's paralleled by StoryGuides and players. And just as canon can be changed by religious authorities (How "saints" are viewed/created, as a recent RL example), so the AM authorities can change game canon. But until you do change it, it remains constant as played and previously understood.
If the Pope decided that Saints needed revising, but didn't tell anyone, there would be one canon according to the Vatican, the (for sake of argument) "Authority", but there would be another "canon" as understood and practiced by the priests and the masses. And they're both "canon" in one sense of the word (just not the same sense). The moment the Authority announces the change, that second "canon" now becomes heresy and outdated - but not until then.
(And while this change in "edition" raises questions with other parts, no other part is changed unless officially changed.)
Because just like RL religions, unless you claim that 5th ed AM is an entirely different and completely unrelated game (and then we wonder why it's called "Ars Magica"), those relations exist - and part of that is the carryover of previous understanding of canon. You can deny it (and I'm sure there is some RL religious parallel there between practitioners and authorities changing religious doctrine), but the fact remains that in practice until it's changed, it's not.
There is canon as decided by the authority, and that canon is then understood and practiced by the masses. These need not be different - hopefully they are not, until a new version comes out. And then, oddly enough, only what has changed has changed.
(Edit - In hindsight, comparing AM to a religion is, perhaps, not the best choice. Certainly some parallels fail. But the dynamics of "canon" within the hierarchies works for me.)
Ah - I see. All this is based on your assumption of that. Or perhaps on some unpublished knowledge, not available to players. Or can you point somewhere in 5th ed core book where I should have understood that?
I'm happy to admit that I'm assuming the opposite, but based on pre-existing canon, as opposed to... whatever your view is based on. If that's the only difference in our views, then... meh.
Not only that, but that has become mainstream acceptance by previous editorial decision (as opposed to any confusion or misinterpretation).
The Houses, the Tribunals, even the Spells, all had quirks and personalities from previously established AM doctrine, from "canon" - I'm saying that those were not changed by default until they were changed by act. The moment a new book came out, they changed - but until then, for players, they had been continuing exactly as they had been pre 5th ed. Call it intertia, call it "assumption of facts not in evidence" - butcha can't say it didn't happen - because for every 4th ed player (who was not privy to internal Atlas secret ninja stuff), it did.
The problem is that the word "canon" is dancing between usages, between an editorial theoretical canon and a player's practical canon.
When you or any editor states "there is no canon", that makes sense if it means that no writer should feel constrained by what was written before - it's open season. If you want to write that House Bonisagus were the ones to become vampires, or that Tytalus are lepers, go for it (might not eventually be accepted, but "there is no canon", so don't let anything previously written stop you as a writer - "no canon").
However, for players, there is an effective canon until those changes are published, even if writers are encouraged to ignore it. There has to be, because players don't know what will/won't be changed. There even has to be for editors, because unless they are, indeed, creating a brand new world from whole cloth, they view the new writing in the shadow of the previous (...say it with me...) "existing canon". They are free to ignore that shadow, just as a new tide ignores sandcastles, but it's still there until it's not.
So - concerns of canon are the concerns of players who care about meshing their world with published material. But concerns of canon are not concerns of players who are not advancing that canon for the product line. And concerns of canon are not concerns of writers if that "canon" is from a previous ed, and the editorial policy is one of change. But concerns of canon are of concern to writers with regard to any aspect that's been concretized, that has been given the official editorial "this shall not be changed" stamp of approval.
The only "wrong" statement is to claim that only some of these apply, or that some are false because others are true.