I have toyed with the idea of adding new aura's to my campaign to represent ancient and possibly largely forgotten forces- it seems to me, for example, that Faeries tend to represent the Vedic pre-genus spirits, while magic auras represent the genus spirits of the ancient greek philosophy, the divine is obviously a more medieval paradigm, the infernal is an anti-paradigm, so I'm trying to decide where else I can go that doesn't seem petty- an epic paradigm of ancient Sumeria? Something Egyptian, or perhaps shamanic? Any ideas, or does anyone else even see where I am trying to go with this?
First off the four auras cover a lot of bases. Notably Magic and Faerie cover most everything. The Divine is Monotheism. The infernal is the dark side of human nature. Magic is everything in the natural world made more awesome, and Faerie is human dreams made real. Magic and Fae pretty much cover everything non-human. The only reason why the Divine isn't Fae, is because it got its own little aura type carved out. If you tried to remove the Divine from Ars Magica Faerie would subsume it.
I think that means you are basically left with auras being human based. Like the Infernal. Their used to be auras of Reason in past editions. You could do something in a similar vein. In past editions they were a rather silly rejection of all the other auras, reason would conclude that the other auras exist and figure out ways to exploit them. You could bring back those. You could also make auras of Reason that actual were reasonable.
I could certainly see some form of aura of epicness. Aura's based on human achievement and greatness. Really that is what the old aura of Reason was supposed to be if I got the writer's intent. I have a hard time seeing forgotten forces though that wouldn't go under Fae or Magic. Maybe some sort of Cthulu-esque Elder Gods would make a good 5th force? Magic isn't alien to the natural world, they weren't imagined by humans (fae), they don't care about sin like the infernal, and they sure as hell aren't divine.
From what I understand of HP Lovecraft, the Elder Gods are very much a physical part of the universe. But they are beyond our understanding, and they simply don't care one whit about our existence.... which is functionally the Magic realm, in AM. Specifically, the Ancient Primordeals (The Pillars, I believe they're called) would be considered the Cthulluesque entities in an AM world, and they're pretty much the definition of "ancient, powerful Magic".
But, yeah - to go for the OP's question - some variant of Reason might be the way to go, or some proto-Humanist aura, or something. However, according to the Mideval paradigm, both Divine and Infernal are completely Rational, so they likely wouldn't be affected by it. (The Divine gets the additional bonus of intuition, whereas the Infernal doesn't.)
An aura of Reason would probably give a bonus to everything, IMO. Its understanding and using the natural world to your benefit. In Ars Magica that very well does include Magic and Faerie. Maybe the Infernal would be penalized. Or perhaps it would give a bonus to humans while oppressing everything else.
Probably not the latter. Again, The medieval paradigm considers Reason to be complimentary to the Divine, and the Infernal has completely incorporated it as part of its toolbox to tempt humanity. Of course, both Farie and Magic certainly operate by a general set of principles - although Farie is "story" and Magic is likely "Idealism". I would argue that such a Reason aura would probably grant a 1/2 bonus to Magic and Farie, and a full bonus to the Divine/Infernal.
I've toyed with a new Aura that has a sort of steampunk magitech feel. It starts the Renaissance, and changes how Giftedness and magic works in the areas which are infested with it. Mainly this is to allow a new set of genre tropes to war with the conventional genre tropes of the game.
When we were having a shot at a China book, we had Civilised and Wild auras (the first being part of the Celestial Bureaucracy and centred on towns (Faerie with the Western associations shaved off), the second being the primordial forces of the world (Magic, effectively).
Almost any human civilization not covered by the Divine should get a Faerie aura almost instantly. And it should conform to the local beliefs.
It also occurs to me that a source of auras could be Faerie "fragmenting". Someone gets a bunch of ideas about "Rationalism" and "Reason", (Which are totally contrary to actual Reason) and you suddenly have Reason auras from third edition. Sure, technically they are really just Faerie auras making reality conform to the story, but it certainly seems like the world runs without any mystical influences in them. It would also give evidence for the Divine really being an oversized Fae.
It's a houserule - You don't have to give evidence to justify it.
Evidence to the Denizens of Mythic Europe. They don't justify stuff via "houserule".
Your saga, your rules. You can have the NPC's believe whatever you want them to.
And like people in the real world NPCs have reasons for believing stuff, not just because the Troupe said so.
Which begs the question as to why you think they should believe that. Which implies that you're ACTUALLY saying that your proposed houserule is "The Divine is a giant fae", and you're looking for additional houserules to support THAT claim.
OK - your saga, your houserules. I don't have any particular in mind that would help with that, at the moment.
Because it makes for good stories for them to believe that.
I'm a secondary GM, with no control over (or knowledge of) the divine realm's nature, but I still have a major NPC who believes that the "Divine" and "Infernal" are both the same faerie-esque entity feeding on people's beliefs.
She's almost certainly wrong, I wouldn't know, but it makes sense in character and it makes for good stories.
What Kingreaper said. If something makes sense in character why not? Plus its not like there is a particularly large number of people who are really right on the Divine anyway. Canonical Divine, is freaky in Ars, and seemingly outright contradictory. Very few people believe in Islam, Christianity AND Judaism in Ars. And, screw it, Pastafarianism because that absolutely does meet the definition of a Divine religion in Ars.
Finally, the idea of the Divine being a god like all the other gods that has gained run-away power, isn't even my idea. It comes from one of the Hermetic Theurgy inserts.
If that's the case, then you shouldn't need an additional house rule to get NPC's to believe it - as has been mentioned, other (in-game) folks seemed to have come to that conclusion by themselves. Some of the characters in the saga I'm currently in have similar views - they consider the Divine to be "just another god" (likely Farie, just because it seems interested in humanity), albeit one that's gotten It's act together better, and has a better PR campaign, than the others. The players didn't need to put together a house-rule to support this. Rather, this is considered the default assumption for all pagan/non-Divine views of the Divine. admittedly, it's a descriptive (organizes available data), rather than proscriptive (allows for predictions), view of it, but it works for them.
If you feel the need to add additional house-rules to support an non-traditional view which already exists within canon, for the express purpose of making that alternative view seem more valid than it already is - OK. Your saga, your house rules.
Personally, I'd question as to why the alternative belief is non-traditional: after all, there is now (retroactively) this piece of evidence that suggests that the alternative view is correct. Has this style of aura been here the entire time, and simply not been noticed? Is it some sort of Breakthrough that is just now appearing?
You seem to be coming at this from the wrong angle, and creating a disagreement where none exists.
At no point did Lamech propose creating the house rule for the purpose of making NPCs believe.
Lamech pointed out than an effect of the house rule would be providing evidence for the NPCs' beliefs.
Yes, I understand that. My point is that such a house rule is unnecessary, given the base conditions of canon.
The claim seems to be that the house rule in question (auras mutating/evolving/whatever into a fake-Reason aura), will, among other things, provide evidence for certain NPC's alternative belief system. My point is that if that it the primary motivation, it is unnecessary - the alternative belief already fully exists, and is at least moderately well-known in theological circles. As has been pointed out, Hermetic Therugy (TM:RE, pg 78) pretty much lays this out as an explicit set of beliefs for some in the Order. More generally, Gnosticism is already known to Mythic Europe - anyone who has read through the New Testament will see evidence of it.
Thus, there is no reason to provide additional evidence for this belief system in order for the belief system to exist. That minimum standard has already been met by means of a number of 1st century Greeks and their decedents. And, if anything, If anything, the schizophrenic nature of the Divine suggests that something is going on behind the scenes. A character can fully believe this, have stories based on this belief, etc. and be well within the basis of Mythic Europe as described by canon.
To summarize: you don't need a change in a game mechanic for someone to believe this or be given evidence for it. You only need for them to observe what normal people observe that lead them to Gnosticism. If that is what the purpose of having the new "mutant Reason aura" in your game is, then I would argue that it's unnecessary.
EDIT - and to clarify: I've gone through Mage: the Ascension/consensual reality/will-working magik-with-a-k. I've done that. It had some interesting game mechanics, and the World of Darkness was an interesting enough place (if you edited heavily for a single game line), but ultimately I found the underlying metaphysic of subjective reality to be uninteresting. Therefore, trying to get the Divine over into "just being a giant farie, subject to human belief like everything else" is, to me, uninteresting. As others have said on other threads, I find that it takes away from the flavor of Mythic Europe to give good evidence for that question. But (once again): your game, your house-rules.
EDIT II - I do consider Fairie to be fine in and of itself, as a sort of "magic by means of human psychic creativity", with Magic being "Magic as inherent mystic/idealized part of the world", with the Divine/Infernal being the "magic as truly beyond nature". I just don't care for "Oh, it's all just Fairie". it's flat and uninteresting to me.
THAT BEING SAID - I think the idea of a Reason aura (as described on the first page) to be fine, as otherwise I wouldn't have commented on this thread - jumping in just to say "your idea sucks!" is something I normally try to avoid. I just don't think that having a splintering farie aura, (and thus using that as evidence that other types of auras are similarly mutated) is a good idea.