I had an idea for a new virtue, and am wondering whether to consider it a minor or major virtue 9and whether to allow new characters to have it mid game)
Great author: When you write a summae on a subject, the level of the text begins at 2/3 of your level in the art or ability instead of 1/2.
That's essentially a restatement of the ArM3 one point virtue Strong Writer, although that also increased your writing speed. I believe Good Teacher pretty much replaced it with a different mechanic, and for both those reasons I would vote for Minor. However, if you combine both Good teacher and Great Author you might redefine the power level of your saga, and thus if you intend NOT to have a high powered sage, I would suggest bumping it to major.
Hi,
I would suggest at least considering to ban this entirely.
In previous editions, I'd strongly recommend banning this kind of virtue. It is easier to add xps to Arts in AM5, so boosting summae is less of a big deal.
But it still Doesn't Belong.
What the virtue effectively does is make good summae quite a bit more common. That great summa that used to require an Art of 40? That's now an Art of 30.
The character himself does not become very much more powerful, except to the extent that other magi are likely to consider the guy who writes the best books in the Order to be untouchable, but the game changes.
This belongs with other virtues that don't have a huge effect but that probably don't belong, such as Minor Virtue: Can effect a class of Essential Natures.
Anyway,
Ken
As I recall, it was one of the reasons 3rd edition was never as popular as the 2nd edition, wasn't it?
It's minor if you use it, but I wouldn't go for it because it breaks the existing curve for academics and especially the Hermetic Arts. For a top-tier writer, the power of this Virtue is roughly ten points, which means that any Hermetic author without it can only write extremely vain summae.
It only breaks the current academic curve if you assume that it's not unique to the player character. If it was, I'd argue it as major if it is going to have a big effect on the plot (House Bonisagus supports you politically, and if anyone declares War on you they rally around because you are vital for Original Research which will break the order's training curve.) then it is Major. If you have it and no-one really notices, you just get to make some books which are better, and eventually write a new Root or Branch, then it's Minor because honestly most sagas fall apart way before then.
That's true. I was assuming that it was a virtue being added to the List of Available Virtues instead of a special bonus to one PC.
I thought it was the demons and painful sex toys. 
But please do elaborate.
You think it was problematic that there is a way to increase the levels of summae in 3rd ed because it led to power inflation?
4th ed only had this possibility through Twilight effects. And the way this worked here had a natural limit because it led to Final Twilight.
But since 3rd ed only had one number stat for Summae it makes the situation with writing higher level books different than 5th ed rules. And I wouldn't like this in 5th!
Probably the main reasons, yeah.
And Reason.
I vaguely recall it being one of the complaints at Berklist, against the 3rd edition when it came out. It was available via virtue or via Twilight (which was new to that edition).
4th edition was a nightmare.
3rd edition made greater Art scores more available because you could write that increasing fraction of your Art. But the Arts would still generally increase slowly.
Then 4th edition brought in Arts based on XPs (by popular demand), which gave rise to ... exactly the increase in powerlevels that it was predicted it would. No more wasted seasons, essentially.
Which combined with early versions of the current guideline/parameters-system to make for an exceedingly powerful edition. I still have the notes I think, for the straight-from-Gauntlet character who could and would build flying castles. Or the fireball to level England.
At least the current edition makes the worst of those somewhat harder.
Agreed.
Magister in Artibus ex Miscellanea. 
Nowhere near as broken as some of the stuff you could do in 4th.
Hi,
A Magister Ex Misc seems a great idea to me rather than overpowered. Nothing about Magister breaks a magus, and the required Hermetic Flaw is probably going to be quite annoying.
Magister/Doctor, Strong Faerie Blood all make great Ex Misc major virtues. They all are very good, as they should be, being major virtues.
Regarding 3ed and book levels, I don't remember anyone other than me complaining back in the day. That might just be my memory though.
Tangentially, I think a decent house rule would be to allow any magus to take 3 extra non-Hermetic virtue points at the cost of a single, major Hermetic flaw.
Anyway,
Ken
Agreed.
I remember having read complaints. I don't remember from how many sources.
I know I didn't complain back then. I wasn't much of a poster then.
Without limit?
In 4e, I recall that Magister Ex Miscellanea was a fairly cheap combo (noble's parma as I haven't had a copy of 4e for a while and CBA to even look and see whether it's still available) because the Ex Misc had a high number of XP but low stats in Latin and other mage-academic skills, a Magister in Artibus had high stats in the latter (note: the MiA didn't get extra XP, he got specific skill levels handed to him), and a magister-mage gets an extra bunch of XP to represent the fact that his parens can spend time teaching him magic instead of Latin and Artes Liberales.
A magister-mage in 5e is legit, albeit a bit spendy. (If you want a tradition using Academic Status instead of a Supernatural Major Virtue, though, I'd go for Magisters in Medicina with some useful knowledge of natural philosophy and a knack for Rego-craft.)
I was thinking of AM5, not 4.
Of course, for the same major virtue, be a Doctor of Something. More xp, though with some spending restrictions. Still, it makes for a great Ex Misc tradition. And if you're the fourth magus of your lineage, you get to wear a long scarf.
Anyway,
Ken
What about a combination virtue that allows writing at 2/3 level and includes a reputation as a great writer and book learner? Or maybe a bigger reputation? That makes it closer to what you are paying for with a major virtue but still makes it more rare and less likely to break the curve.
I'd still Just Say No.
It isn't about character power: On these forums, I tend to be way out there in favor of magi having power and supporting bleeding heart liberal rules interpretations and modification to make that possible. I don't believe that powerful characters break the game, though certain GMs do break.
On the other hand, I am sensitive to rules and rules changes that pertain to the entire setting. Probably overly sensitive. One doesn't need many characters with this kind of major virtue to completely change the literary landscape of Mythic Europe. So combining a "let's break the setting a little" virtue with a Reputation virtue and one of the best minor virtues in the game doesn't help me any.
It also isn't likely to win friends among the "anything that's good is too powerful" crowd. Putting on that hat for a moment, and only for a moment because the hat feels too tight and it itches, I start wondering why Good Teacher isn't a more appropriate virtue. Or maybe a minor Essential Whatever virtue that provides +3 Com when it comes to teaching. (Then tank Com for other stuff 
.) Or both. And then take a good reputation and Book Learner. All of this lets a person write awesome books, without changing how things work.
Of course, one can argue that things don't really work... /2
Taking off the hat, and looking at how AM5 does work, a virtue of the kind you describe sounds very much like a Breakthrough that transforms the nature of books or education in Mythic Europe. The level of Breakthrough? Probably not too huge a breakthrough. But also not something that anyone actually has.
As I write, I start wondering what an experimental book would be like. You know, publish experimental books to push toward a Breakthrough and let society react. Botch, and maybe the Dominicans show up or the book is so good that your apprentice is literally sucked into it....
Anyway,
Ken
I often find myself in the group who thinks "if something is this powerful is shouldn't be that easy, because then where is the fun?" And being an old fart in ArM and with a tendency to go look for clever combinations, hacks and synergy I often find myself here.
For me it's both a matter of what is best for the saga and stories and also what's best for the balance of the saga - balance between players. If one player is very clever it creates a chasm between his character and the rest. Some situations which should be a challenge to magi of this age, and which are challenging to the other magi, are a breeze for him. And what constitutes a challenge for him is lethal or impossible for the rest, so they don't want to participate. IMHO this ruins a saga. If all the player magi go down some avenue where utilizing a clever method means they become powerful together, and if the rest of the Order doesn't also do this, it changes their role in the saga. THis cna be a good thing, or a bad. Do it if you want to. And finally, if everybody uses the same hack PC and NPC magi alike then the general power level rises and the poor SG may need to rethink which challenges he throws at them, to ensure the stories flow the way the Troupe wants it to.
The way study works in 5th ed I would not like an "increased understanding" virtue.
In 2nd ed writing books was a binary thing, you either do or you don't. Only one type of book, only one number to rate it, a score up to half the Art of the writer. The more skilled the author was in the subject the better the book was. Advancement in full levels of 1-3 depending on what the book's score was compared to your own. A good book was not only faster to advance with it also was usable for a longer time. The author's ability to write, Communication etc. was not relevant.
3rd ed had the same writing and advancement method, but Strong Writer virtue could allow books of 2/3 your score rather than ½.
4th ed had much crunchier writing rules, and more detailed advancement rules. There were several types of books, but let's focus on the summae. Summae were rated for both Level and Quality. Writing was for level still capped at ½ Art score, but some Twilight Effects could lead to increased understanding increasing the cap through the fractions 2/3, 4/4, 5/6 etc. Quality was now based on Com plus the ability Scribe. Strong Writer virtue gave +3 Quality to books written, plus it allowed for faster writing and copying. Plus WGRE had rules for the book's physical quality, where the aestetics of the author's handwriting could play a part (based on rolls of Dex + Scribe, so there was a random factor), plus bonus for illumination, coloured inks, good quality vellum, binding etc. Seldom more than a +3 bonus, but it added to Stody Totals. But wear and damage to the books could reduce the Physical Quality.
Advancement was by exp not full levels, and included Int + Concentration ability. So you could invest expereince point in a ability in order to be better at styding for experience points.
WGRE had some rules for when a second magus added something to a a book he had read. Glossing was by far the potentially most unbalancing. A magus who had spent even a single season reading a given book could make corrections to the grammar and contents, effectively changing the book's Quality to what he could write. So if the original magus had huge Art scores, Increased Understanding (from Twilight) but was a horrendous author woudl write a summa with a huge Level but abysmal Quality. His friend who had but low Art scores rad the book for a single season and used his good Com + Scribe + Strong Writer to change this poor Quality to a high one. And if he had a little luck with his Dex + Scribe and combined with spending money on good vellum, inks, skilled illuminator and binder it would end up with a high Physical Quality as well. This could easily break.
in 5th ed, for a magus to write a really good Summae he would need not only good Art scores but also good Com and also really Strong Writer - if he wanted to compete with the masters from the past. More balanced IMHO. While I don't think adding a virtue enabling the author to write 2/3 his Art would be as unbalancing as the 4th ed example, it would certainly change things. It would mean a skilled author with increased understanding would either need lower Arts to write an book equivalent to his counterpart without this new, suggested virtue. Or at the same Art scores his book would be better.
While this would potentially change the upper end of the scale for Summae levels than what the RAW suggests, the really, really good books would only be produced by magi spending 4 virtue points (for Strong Writer, Increased Understanding, Great Com x2) and maxing Com. So wouldn't there statistically be less magi with this exact combination compared to magi with only 3 of these? Probably!
But would there be many of these seen among PC magi? Most likely, since this is a powerful concept. Writing awesome books means you have a lot to trade with, for vis or favours. So if a saga runs with 1-2 PC magi as legendary authors as the only ones on the tribunal, then things may get unbalanced.
Indeed. Some virtues tend to crop up together, especially in PCs.
Experimental books would obviously come with the risk of the book developing sentience and then eating all the members of the covenant.