I saw a reference to something involving Superman the other day that qualified something as "Canon" because it had occurred in a DC comics story at some point. And I laughed.
Superman first appeared in 1938, about eleven years after the last new Sherlock Holmes appearance in our Holmes Canon. Jerry Siegel and Joe Shuster, Superman's creators, worked on his comic book for about ten years, and then left it behind for other creators to take over. And in the ensuing nearly seventy years, a whole lot of writers and artists have worked over the character, changing his powers, his origin, his love life . . . you name it.
If you thought Dr. Watson had some inconsistencies . . . phew!
But that's because all of those Superman comics aren't his Canon. They're mostly pastiches of what Siegel and Shuster did in the 1930s and 1940s. Most of those pastiches are better than the originals, yes, but still pastiches. Copies. Professional fanfic.
This is where Sherlockians get to put on airs. There is a lot of talk about Canon in a lot of fandoms these days, but ours, in the original Holmes sense, comes in actual one-book form. It has a beginning and an end, and is not subject to corporate rewrites at any given moment. Superman, Star Wars, even BBC Sherlock could have a sudden decision by the powers-that-be to make the main character be turned into a cow by a magic fairy, t'were the wrong person to get into the wrong position at some point. Public domain, ironically, keeps Sherlock pretty stable, Canon-wise.
Was the word "Canon" used in a non-religious sense about a group of stories before the Sherlockians of the 1930s picked it up? I'd be interested to hear of such a thing. But getting us back to the religious origins of "Canon" gets us back to the real sense of the thing.
At the core of anything called "Canon" is that one person has defined that body of work as holy writ for their personal life choices. At least one actual person. The fact that we now have the term "head-canon" is kind of amusing, because it's all head-canon in a way Someone's head decided that something was their Canon.
But I do like "head-canon." Saying "my head-canon is this . . ." is a really nice, non-threatening way of saying, "I like to think of it this way" or "My opinion is this" without the listener fearing you're going to try to convert them. The subtle implications of "It's in my head and you probably have something different in yours" couldn't be more perfect.
Yet sometimes we do need a common point of reference for those things outside our head, and that's where "Canon" can get dicey, especially with corporate properties. Thank goodness that Sherlock Holmes got his dibs in early, and The Complete Sherlock Holmes by A. Conan Doyle got commonly accepted by all concerned before the modern era.
We may never see its like again.