Being a member of a tradition has mechanical advantages, including giving you Favoured Abilities / Arts and Magical Defenses. However, it's not entirely clear to me how traditions are formed in the first place.
Unless I've missed something, there aren't any rules for creating your own tradition. There is a canon example, though: Bonisagus. His approach appears to have involved some combination of original research and integration.
So presumably the process for creating your own tradition involves some similar combination of research and investigation of existing effects. You would need at least one relevant successful project for each ability / Art of the new tradition. Questions I have include:
What level would the breakthrough need to be? I was originally assuming it would be a "Hermetic" breakthrough, but I'm wondering if that actually needs to be the case, or if a Major Virtue would do (if you don't meet any of the other qualifications for being a Hermetic breakthrough, such as the tradition breaking a lesser limit). HoH:TL does note that the Parma is the only Hermetic breakthrough that has occurred in the 450 year history of the Order (you can quibble that the invention of Hermetic Magic was outside that period, but so was the invention of the Parma).
Can you get a Magic Theory as part of the breakthrough, or does that have to be a separate invention? You clearly don't always do so, as a number of traditions don't have one. It does look as though Bonisagus may have done, though?
Getting insight when you don't have a Magic Theory is hard: Int + Insight Bonus/ Penalty + stress die vs EF 18. Inventive Genius adds +3, and is more or less obligatory, but is there anything else that will help? Presumably you can't get a teacher, because they would have to be part of your non-existent hedge tradition, but I'm wondering if the rules for using a Gifted person with the relevant ability as a lab assistant would work? They'd only be adding their intelligence, but that could be substantially better than nothing. I'm wondering if they would also add Inventive Genius if they had that too?
It feels like creating a new hedge tradition with a number of things that Hermetic magic couldn't do would be easier (or at least, require fewer breakthrough points) than integrating those things into Hermetic magic. Is that reasonable? The main argument in favour I can see is that it's easier to structure your tradition around them than it is to rework them into a Hermetic framework.
See the sidenote in HMRE p. 16 "Hermetic use of Hedge Theory" for inventing a hedge magic theory. It is a hermetic breakthrough, but can be simplified by being skilled in an existing MT or hedge theory.
As far as I know, it doesn't apply, no. The check for insight on original research isn't a lab total. The one advantage of working together would probably be pursueing seperate sources of insight and then sharing with each other.
With the caveat that you will probably be using your Magic Theory score to make that original research. I'm not sure, I tend to lean towards the no, but I'll read here to see what is said on this point.
Ah, yes, of course, (Hedge) Magic Theory is an arcane ability, which makes creating a new one an automatic "Hermetic" Breakthrough (although, weirdly, so is Code of Hermes...)
So you definitely can't create a new tradition with a Magic Theory with a Major Virtue. In which case:
Can you create a new tradition complete with Magic Theory as a "Hermetic" breakthrough, or do you have to:
Create the new tradition first (with either a Major or Hermetic breakthrough), then create the Magic Theory as a second ("Hermetic") breakthrough?
Obviously the second approach will always be an option, but is the first? It could make some sense for it to be possible to create a basic tradition with no Theory as a Major breakthrough, or a more "refined" one with a Hermetic breakthrough, but requiring multiple breakthroughs also works. Did Bonisagus make two great breakthroughs, or three? He's generally only described as having done two (e.g. page 9 of the corebook, ""He made two great discoveries, either of which alone would have ensured his place in magical history. The first was the discovery of the Parma Magica...the result of these studies was Bonisagus' second great discovery, they theory of Hermetic Magic".
So I'm leaning towards it being possible to combine the creation of a tradition with its magic theory?
Sorry, "lab assistant" was the wrong phrase there. I was thinking of the quote from Hedge Magic (pg15):
"In addition, a Gifted teacher can act as an assistant to the Hermetic magus, in which case add the teacher's Intelligence + (Hedge Magic) Theory to the magus' when making rolls to produce an Insight Lab Text. A teacher may only assist one magus in a season, and a magus may only be assisted by one teacher each season when attempting to find an Insight - this is because additional teachers tend to confuse the issue with their own interpretation."
This is ignoring that before he even invented the Parma he studied ways in which to use the magic he knew, the Mercurian Tradition, in new ways that were less dependent on large, group rituals. This may not have been so much of a discovery in the Original Research sense as collecting diffuse knowledge spread around and then he continued this work and integrating the magic of other traditions (Diedne and Bjornaer and, presumably the Witches of Thessaly via Trianoma) after he collected those folks to teach him but the initial work that was likely almost solely a refinement/modernization of the Mercurian Tradition should not be overlooked.
I was treating "Discovery" as a fairly broad term, which included "integrating various bits and pieces into a new tradition".
It does raise the interesting question of whether Bonisagus actually switched traditions, though, or whether the entirity of Hermetic Magic is just an extension of his original tradition (presumably a Mercurian offshoot). I'd lean towards "entirely new", on the basis that it appears to have different magical defenses (and presumably also a different Twilight response, although given that that's meant to be an addition from Criamon you could probably make an argument for "integrated it which changed the existing tradition").
For reference, the character I'm currently thinking of who's trying to create a new tradition has no existing tradition, just some accelerated abilities she's trying to form the tradition round (along with new abilities she's trying to pick up).
In "The Mysteries" there are rules for creating one's own cult based around some mysterious discoveries. I would suspect the easiest path would be the create a Mystery surrounding a breakthrough, and then grow it form there?
I've always though that Bonisagus' genius was divinely inspired, given how well the Order of Hermes has worked out for Christianity in general. Pagan cults were absorbed and basically stripped of all religious elements (or eradicated as the Diedne were), leaving a group of relatively isolationist magicians with pro-Christian tendencies. The Order also smacks down any Gifted individual who deals with Infernal powers and harvests dangerous magical beasts (and faeries) who might otherwise threaten ordinary Christians. And while the Gifted might not be exactly what you'd call well adjusted, they're much better socialized than non-Hermetic Gifted and less prone to things like murderous rampages and cataclysmic displays of power, despite being FAR more powerful than most non-Hermetic magi.
When I was actively running games, and came across an observation like this, you always go back to the "Ineffibale and unknowable Divine Plan" (And the fact it is possible to become a Dominion Magus in the RAW shows the plan can include conversion of Magi)
A also think that one possible endgame of a Criamon character is becoming a Dominion oriented Magi, given the 5th Ed treatment of them.
But there is an undercurrent that Magic and Dominion are more on the same side than not. Though the relationship is asymmetrical since the Dominion is far more powerful and doesn't actually need allies ultimately in the RAW.