The Tolkien fan community broadly agrees on three levels of canon:
- Works that were published in Tolkien's lifetime (so The Hobbit and The Lord of the Rings
- Works published after Tolkien died (typically excluding the drafts of Lord of the Rings; it's a rare fan who'll argue that Trotter supersedes Aragorn in the canon)
- Non-Tolkien works, like the Jacksonverse movies (which have the own internal canon, which is wholly out-of-scope for this question) or The Last Ringbearer
But calling these "levels" of canon is abusing terminology a bit; these "levels" don't really imply a hierarchy, but are more about our degree of confidence in the canonicity of the given work:
- Most everybody agrees that works in this level are canon1
- There's some debate about works in this category; the debate is mostly around the published Silmarillion versus the History of Middle-earth drafts, but there are also arguments about whether Tolkien's essays should be considered canon
- Most everybody agrees that works in this level are not canon (or at least not in the same canon as the novels). While they may be amusing or interesting on their own merits, few (if any) fans will seriously argue that they can be true simultaneously
Of course the question is focusing on the debate surrounding Tolkien's posthumous works, so that's what I'll focus on as well.
Is there an official canon?
Yes, but it's not a helpful one.
The thing about canon is that, in order for it to be useful you need someone to arbitrate it; there needs to be somebody all fans can trust who says "this is canon" and "this is not canon". In Star Wars, for example, this is the Lucasfilm Story Group, a division of Disney with no other purpose but to manage the Star Wars canon.
With the Tolkien Legendarium, the only reasonable person to take on this role is Christopher Tolkien (and the Tolkien Literary Estate more generally). The problem is that he isn't interested in a cohesive and internally consistent canon, as he writes in the foreword to The Silmarillion:
A complete consistency (either within the compass of The Silmarillion itself or between The Silmarillion and other published writings of my father's) is not to be looked for, and could only be achieved, if at all, at heavy and needless cost. Moreover, my father came to conceive The Silmarillion as a compilation, a compendious narrative, made long afterwards from sources of great diversity (poems, and annals, and oral tales) that had survived in agelong tradition; and this conception has indeed its parallel in the actual history of the book, for a great deal of earlier prose and poetry does underlie it, and it is to come extent a compendium in fact and not only in theory.
The Silmarillion Foreword
See also the structure of the History of Middle-earth series: Tolkien's notes are presented, warts and all, with minimal editing and surrounded by commentary that provides context and narrates the changing conceptions.
While interesting academically, this isn't really helpful for fans; we want to know which version is "correct", something Christopher Tolkien is wholly uninterested in.
Is there an unofficial canon?
In the absence of an authoritative voice saying "This is what is canon", it falls to individual fans to decide on their own. Ultimately you have to take every inconsistency on a case-by-case basis, and decide for yourself what bit is canon. You can look at what other people have decided to give yourself a guideline, but saying that one fansite's interpretation is more objectively correct than another fansite's is wrong on many levels.
As one might expect, this is something fans argue about a lot, and a cursory Google will reveal no end of attempts at reconciling the canon. A personal favourite is this discussion on Michael Martinez's blog; while I don't necessarily agree with everything he says, I think his ultimate point is a good one:
"How do you pick and choose your texts?" I am sometimes asked.
I like to say, "Carefully."
"Is Your Canon on the Loose?" Middle-earth and J.R.R. Tolkien Blog by Michael Martinez
Probably the two most common (broad) approaches are described on Tolkien Gateway:
Final intent. Basically, Tolkien's later writings take priority over his earlier ones. This is the version I personally favour, because it allows for the fact that Tolkien's ideas shifted as he wrote The Lord of the Rings
Height intent. This version prioritizes the final version of the Legendarium as written in History of Middle-earth V, everything pre-Lord of the Rings. I'm not a fan of this one personally, because it seems to fundamentally misunderstand the nature of writing2
However, probably the most useful I've seen comes from a fan named Michael Kane . Kane proposes three levels of Tolkien canon, which depend not on the works themselves but on the purpose of the discussion. Kane's levels are:
This is the arm-chair level of canon and the easiest one to use and talk about. This includes the major published works, The Hobbit, The Lord of the Rings, The Silmarillion, and probably the Children of Hurin (Not previously mentioned). This is the canon that anyone can pick up and have a conversation about with their friends. It takes The Silmarillion as is.
We can presumably lump The Tale of Beren and Lúthien into this group as well.
This is the one that mostly leaves out The Silmarillion in lieu of other manuscripts. This canon is comprised of late versions of The Silmarillion. Whatever Tolkien wrote later in his life is generally expected to be accurate in this case. (The Hobbit and LotR are included here as well, with a special understanding of The Hobbit that may come up on a later day.) This is the canon that Tolkien enthusiasts talk about, waxing eloquently about specific versions of specific stories written at specific times. Most people aren't interested in this one.
This one doesn't actually exist. This is The Silmarillion as Tolkien would have eventually published it. Perhaps even more accurately then that, this is the version that Tolkien would have considered to be the “true” one, the events as they actually occurred with Tolkien's human meddling. Why do I consider this canon important? Frankly, while the Academic Canon is fun and entertaining to talk about, there is a fundamental flaw in it. Simply because a given writing was the last on a particular subject does NOT mean that Tolkien, had he lived longer, would have changed his mind again. The Histories of Middle Earth document many such changes over the course of decades. We don’t and never will know what the ideal canon looks like.
However, this strategy isn't exactly useful when trying to arrive at an internally-consistent canon; it's a place to start a conversation, not where you go to end one.
Should there be a canon?
I want to return to a comment by Christopher Tolkien that I quoted earlier:
[M]y father came to conceive The Silmarillion as a compilation, a compendious narrative, made long afterwards from sources of great diversity (poems, and annals, and oral tales) that had survived in agelong tradition
The Silmarillion Foreword
This introduces the interesting idea that not only isn't there a definitive Tolkien canon, but that there shouldn't be. Obviously that doesn't hold for our purposes on SFF.SE, but it's worth thinking about: very few (if any) mythologies have a single, self-consistent canon; the kerfuffle over King Arthur's sword(s) is just one example out of many.
From this perspective, attempting to wrestle the Tolkien Legendarium into a single box is an exercise in missing the point.
I mentioned this flippantly in a footnote, but it's worth pointing out that there is a more-or-less recognized pecking order for non-Tolkien authors, particularly works of Tolkien criticism. Although the number of people studying Tolkien is legion, I'll describe some of the more commonly-cited here.
Wayne Hammond and Christina Scull are generally recognized as the leading Tolkien authorities, after Christopher Tolkien himself. In addition to editing several publishings of Tolkien's own writings (including The Letters of J.R.R. Tolkien), they've produced several reference and critical works; the most famous of these is The Lord of the Rings: A Reader's Companion
Douglas A. Anderson's The Annotated Hobbit is viewed with some authority. While not strictly speaking a work of criticism, it does include some insightful analysis of the work, and of its connection to the greater Legendarium
John Ratlieff's The History of the Hobbit is also well-regarded; it was written in similar style to the History of Middle-earth series, and has been endorsed by the Tolkien Estate (Christopher Tolkien wrote a foreword for the second edition)
Karen Wynn Fonstad's Atlas of Middle-earth is a pre-eminent work (iwhat it covers is pretty self-explanatory), and based on extensive research and knowledge of geography and cartography
On a sour note, David Day is a Tolkien writer of dubious repute. His books, especially A Tolkien Bestiary are criticised for deviating from Tolkien's writing. Day's defence, that his books provide a good overview to casual readers, is true, but nevertheless he is not regarded particularly highly as a source
There are more, of course: Michael Martinez's blog is rather good, though I find myself disagreeing with him as often as not; Robert Foster's A Complete Guide to Middle-earth is an excellent reference, and is what Day's Bestiary tries to be; Ask Middle Earth is a more recent entrant, and I don't have much to say about them.
It should be noted, though, that even the best of these isn't flawless, and so should be treated with some skepticism.
1 Though this is kind of a false confidence. As KutuluMike (correctly) points out (correctly) in comments:
[W]e tend to afford higher status to the published works because there's a least some sense that Tolkein [sic] was "done" with them. However, given the major revisions to the Hobbit to fit within LotR I think that's a false sense of finality: had he published another novel, who knows what changed he'd have made to the LotR books to match?
On some level this is, of course, true of every fictional work; that's basically what "retcon" is. But it's arguably more relevant with Tolkien's works, partly because he demonstrably changed "canon" in later editions of some of his books, and partly because he was a notorious perfectionist who spent the better part of his 81 years revising the canon
2 As one fiction writer said, "All writing is rewriting"