Covenants chapter 7 under "Hermetic Book Cycle - standard texts" states 'For nine of the Arts, there is a basic text that, over time, has come to be accepted as the preferred primer for a magus seeking the competence necessary to train an apprentice'. Lower down it reads 'In eight of the Arts, there are summae that are widely accepted as the finest works yet produced'.
Does it state anywhere what these arts are? Better still would be the names of the texts.
these texts were not defined. I believe that they were left undefined on purpose to allow individual storyguides flexibility. I suppose we could all suggest names for you if you'd like.
Yes, I think this is purposely left open for storyguides to fill in. For instance in our campaign, one of our Bonisagi Pater is famous for writing introductory text to all the Arts. These books are by no means the most saught after books in the Order. Quite the opposite, they are probably the most common book in the Order and nearly every book taught student has learned something from these books. We have always said they are "The See Spot Run" books of the Order of Hermes. Incredibly simply and incredibly accessible. Having authored these books has resulted in the Magus become super famous because everyone knows his work, even if it isn't particularly exceptional or technical.
This sort of nuance is left open for individual campaigns to fill in as they like or need. The story is about your characters, you might as well make them important or related to important people in the Order. Perhaps in your campaign, one of the magi is linked to the lineage of one of these exceptional authors.
My concern was that somewhere they've been listed, causing later problems. I like a certain amount of guidance and am REALLY enjoying the Ars5 supplements but I am concerned that they are coming a little restrictive. (And I do know that I can, as Storyguide, always ignore what I don't like.) (And I do know not to start a sentence with And.)
Assuming no one pops up with a reference to a published list then I'll be inventing these as the idea seems very reasonable to me.
I think we should add a library section to the wiki where people can put book ideas and fluff text.
In our saga, one of our books is Foundations of Theory by Claudius of Bonisagus, which is a summa combining all the techniques at Level 5, Quality 15, and Magic Theory at L. 5, Q. 10.
I'd have my players drooling if they got your Foundations of Theory. Too scary for words - they'd fight to use it first ....hmmmm
If you treated skill levels as a continuum, there would be little difference between books of quality 14, 15 or 16. But if you assume that, beyond being a mere game mechanic, Mythic Europe writers have some awareness of the existence of discrete skill thresholds, the optimization metagame does carry over to the perceived value of individual books.
That means that, if your target audience is raw novices, a L5 Q15 summa is worth significantly more than a L5 Q14, while a L5 Q16 is only a marginal improvement.
Beyond merely maximizing Level and Quality, a writer needs to know his target audience, the goal being to let them reach a threshold as efficiently as possible:
Initial skill level
Target skill level
Expected study time
Reader's aptitude (Poor Student, Book Learner, Study Bonus, Affinities...)
While Roots should be at least L5 Q15 to fulfill their role, I am of the opinion that standard texts should benefit a wider audience than the "average magus", and thus should be useful to both poor and exceptional students. In fact, with L+Q=20, the guidelines in Covenants indicate that this would be a rather poor book, maybe justifying their relative cheapness ("Yes, of course I will let you copy it."), but probably not their status.
If you increase their quality to 18, they become useful even to magi with the Poor Student flaw. However, exceptional students will probably find them tedious ("Why did he waste so much time on something so obvious."). We can up the level a couple notches to L7, catering to all but the most exceptional (Book Learner + Affinity) reader, letting them squeeze a little extra out of the book.
L7 Q18 give a total of 25 points, in the "vain summa" range: neither treasured nor worthless, they can be available from many sources, magi won't mind letting you copy them, give them away when they're through with them... On the other hand, I don't think they should really be perceived as targetting level 7 (they would compare poorly with other level 7 summae), but rather as targetting level 5, with some extra insight for advanced students. That would alleviate the "vain summa" stigma.
I thus think that L7 Q18, with individual variation, is a fair guideline for "The Roots of (Art)", accepted standard primers.
For higher level books, such as the Branches, there certainly is going to be a lot more individual variation: the level of knowledge expected of the target audience, as well as the number of seasons the book is supposed to be studied for can vary widely. On the other hand, tractati become increasingly attractive as level increase.
I have done a quick comparison between skills and arts based on the guidelines page 8 and the amount of experience needed:
basic skill 2 -> art 5
moderate skill 3 -> art 7
skilled 6 -> art 14
very skilled 9 -> art 20
Note that the minimum skill level (2) required for training someone (see page 164) exactly matches (15xp) the minimum art level (5) for properly training an apprentice. I don't think that's a coincidence. 
So, an excellent (Q+L=35) summa can take you from 7 to 14 in one year, with a bit of wiggle room for gifted readers (L15 Q20). Alternatively, Q20 L15 can take you from 14 to 20 in about two years of study, while still being better than most if not all tractati.
Anything in that range could qualify as a Branch, depending on your tastes.
Incidentally, for people who want to play with numbers in a spreadsheet:
xp = art*(art+1)/2
xp = 5ability(ability+1)/2
art = (square_root(8xp+1)-1)/2
ability = (square_root(8xp/5+1)-1)/2
I haven't really investigated numbers for ability summae.
Using the max of 21 points the obvious way to go for an intrductory summa is level 6 quality 21. This is a choice I might use for a root of an art (although I'd also be ok with 5/15)
I don't know... It's too obvious. 
I write this bit of the Library section, and no, these books are not defined anywhere.
The author has spoken - that's good enough for me. Thanks.
Serf's parma, but... A book of that quality requires an author with a Com of 5. Are there going to be enough Ciceronian authors in the Order to produce more than one or two of those books? (Perhaps CrMe rituals to boost Com are more common than I'd thought...)
Nathan
Well, the order has been around for four hundred years, and books persist after the death of the authors, and we are talking about a population of mythic people...
Does the Good Teacher virtue give a +3 to the Quality of books you write? +3 Comm and Good Teacher would have a base Quality of 12, not 11, and +5 Comm with Good Teacher would have a base of 14, with a potential Summa quality of 28. I don't know if the level limit on texts is supposed to be absolute or merely to keep starting covenants from having Really Good Texts; if it is absolute then, well, +2 Comm and Good Teacher is as good as +5 Comm, and probably a lot more common.
I think that com boosting rituals and good teachers are not uncommon. Also a quality of twenty one level 6 summa could be created by a character with com +3, art level 36, com +2 art 38 or com +1 art 40. I don't think that any of those scenarios are particularily unlikely for characters more than 100 years out of apprenticship.
I thought there was an issue with bonus not being more than double.
Summa quality: Com + 6 + character bonus + writing low text bonus.
1 + 6 + 14 (40/2 -6)
But the 14 is capped by 1+6, so it's really 1+6+7 = Quality 14.
I just checked my book. You're correct. I never noticed that rule previously. So it takes either +5 com (possibly by stat boosting spells) or +2 com and good teacher. (Or we could go back to the covenants rules and look at a glossed book with lots of resonance, was there ever errata posted on the covenants stuff?).
Of course, as I noted on another thread, I think one your warping score gets high enough there's less of a drawback to pileing on additional warping because one more twilight will finish you anyway. So I don't think stat boosting the communication of old fogies who know allot would be out o fthe question. (It may even be given freely in hope of a pile of quality 11 tractatus)
I'd figured that rule was the origin of the Quality 11 limit on tractati, and Quality 22 limit on summae. Com 5 + 6. But then I found Good Teacher and now I don't know how to regard the limits.
Serf's parma, but I believe that you'd only get 1 warping point since stat-boosting spells are momentary Creo rituals - and none if the spell was made specifically for you.
Again, serf's parma, but I recall one of the sidebars in Covenants noted that the maximum limit on a tractatus was 14 - w/o using the new library rules. My guess is that the suggested limit in the core book didn't account for Good Teacher.
What interests me about Covenants' book quality guidelines (in terms of Quality + Level) is the implications they have for the composition of the Order. Before Covenants came out, I had assumed that the power level of a "typical" book was a lot lower. Covenants' book quality guidelines would seem to indicate that authors are more powerful and better authors than I'd anticipated.
The second point - the higher standards of literary proficiency of Hermetic authors - would seem to imply either that CrMe stat boosting rituals would have to be reasonably common (for aspiring authors, at least) or that Great Com and Good Teacher are noticeably more common among Hermetic magi than they were in the characters generated by my saga's players.
Nathan
I assumed that the spell would be cast multiple times.
the limit in the core book IIRC was for the covenatant creation chapter it wasn't an absolute limit it was a limit of what you could by with your points.