In the Nineties, the fictional land Narnia existed.
The description "existed" might be too strong—more on that later. Without doubt, though, adapted textual representations of it showed up for long time periods on the internet thanks to MUSH software. As suggested by its lighthearted name Multi-User Shared Hallucination, it resembled interconnected advanced chat rooms embedded in an expanding multiplayer "game". Through their role-playing dialogue and software commands, MUSH "players" (world builders?) collectively fashioned virtual realms. By their mostly implicit mutual agreement to collaborate and follow that realm's distinct mythology, they populated/enriched it as they wished without transforming it into something unrecognizable...and therefore no longer appealing to them.
I recalled MUSHes after a point I raised at the start of the the last entry's penultimate item. I noticed that if "[...] followers of deeply organized/defined faith-beliefs still depend on unstated tradition spread through attitudes and norms and conventions," then their efforts to enjoy, preserve, and develop their joint faith-beliefs are analogous to the efforts of MUSH players. Inside the boundaries of a Narnia MUSH, players instinctively know that centaur characters may not carry laser guns or complain about the Seinfeld series finale. One might say that a "Narnia MUSH" with those elements wouldn't be a Narnia MUSH.
Meanwhile, inside the conceptual boundaries of joint faith-beliefs, followers abide by their own collection of unbreakable principles, not all of which are plainly described. For example, in practice they may forbid one another to propose that their supreme supernatural entity could experience surprise. Like MUSH enthusiasts they delineate the content that unites them, so their process and their content are fairly "MUSHy".
Indeed, their content cannot avoid being MUSHy, i.e. socially determined, as long as the customary methods for extending and/or corroborating it are largely non-transferable among ordinary followers. Individuals cannot even imagine how they could fully comprehend, recheck, and reconstruct their joint faith-beliefs without counsel. They cannot explain or recreate the mystical realizations contributed by elite past/present followers. They might have designated texts to analyze, but they cannot plausibly translate the texts into an identical detailed set of joint faith-beliefs, unless they have the necessary supply of standard guidelines/clues/addenda. (At first guess, a Narnia MUSH seems like it would have an utterly simple relationship to its "source texts". No, the "Narnia" lands in the MUSHes, in accordance with players' consensus, purposely improved the book series' original Narnia in a few aspects. Plus, blanks needed filling. Although the series had "Chronicles" in the title, it was tightly focused on the adventures of selected characters, not on an exhaustive account of the lands' history and geography and ecology.)
Consequently, MUSHy content has a self-referential nature. MUSHy content is valid...because the MUSH declared that it is. Each piece of content's acceptability builds on nothing beyond the pooled verdicts of past/present followers and its consistency with the rest of the historical, conglomerated, favorably rated pieces. Coherency is paramount, and it's assessed by trusted insiders. An external or standalone objection to their content is prone to being assessed as incoherent. And that negative assessment isn't necessarily affected by promising bases for the objection, such as alternate readings of their authorized texts or followers who have alternate views than theirs but major tenets in common.
Broadly speaking, MUSHy self-referential pieces of content are cultural realities, which interact with the real mental and physical actions of the culture's members. Sometimes the members are passively swayed by cultural realities. Sometimes they actively adapt the cultural realities in return. Money functions as a medium of exchange because everyone is willing to exchange money. Rulings on legal matters cite previous rulings on legal matters. The conversational rules for a language dialect are laid down by the conversations of the dialect's speakers. A cultural reality is bigger than the humans who live in its shadow...yet its sole toehold on realness is whatever humans do about/with it.
So, Narnia did "exist" in the MUSHes...but only in the shape of a cultural reality. It certainly interacted with the MUSH players like a cultural reality, such as consuming their time and creative attention. While the effects on players are enough to convincingly demonstrate existence as a pastime and as an artifact of bytes, these aren't nearly enough to convincingly demonstrate a land's existence. To be clear, aside from this very blog entry, nobody has contended that the content of the Narnia MUSHes existed in the same ways that a land does.
And that's the pivotal distinction between this analogy and joint faith-beliefs. By definition, faith-beliefs are ideas whose implications cannot be sufficiently verified using substantial corroboration. But faith-beliefs can thrive anyway as ongoing social projects. Like the Party of Nineteen Eighty-Four, followers can reinforce each others' visions. They can share the burden of adroitly harmonizing their earnestly desired faith-beliefs with unverified (or contradicted!) implications. Unfortunately, also like the book, they can become menacing as soon as they aspire to forcibly pulverize the whole outside universe of human understanding into the MUSH they adore...