It is interesting (at the opposite of what I found about your laboratory houserule).
In your exemple, why do you divide by 20 not 22?
In your system, where do the level of knowledge of the writer come into account?
Is it possible, for example, to write a 0 - 40 book?
Thank you
A botched proof-reading. edits
"Author's Magnitude of current art (alternatively the author's score in the corresponding mundane skill)" in the last bullet point.
Of course you can. But it's time consuming like writing encyclopedia britannica. I imagine that house Bonisagus could coordinate a project like that. For example by letting, say 20 magae, writing at the same time (writing different Ranges and then collecting them in hundreds of volumes)
Also. As a rule of thumb, I imagine that every book on arts/skills is one volume per 10-20 exp.
They´re meant to be different after all so no surprise really. Tractatus is meant to be a short work on a specific and narrow subject within an Art or Ability while Summae is supposed to be a comprehensive coverage of the whole Skill.
Personally i find it highly preferable to keep different rules for different books.
Well, the skill you can gain from reading about a narrow subject only goes so far.
I just about never do that anyway. It´s a tiny "flavour" bonus for a lot of work.
And someone outside of that range gains absolutely nothing?
Mmm, that´s a version of calculating time to write i hadnt seen before. Interesting variant. Although i dont think i would use it as it becomes silly hard to write something really broad, and it makes for a rather odd "plateuing" of subjects, ie. it makes you specify that writing about this or that within this Art i get a level 18-19...
Gets rather strange.
Zero bonus from Language?
That´s an interesting limitation. Perhaps slightly "over the top" but i do agree that it makes AL more useful and that it should be.
My rules for books uses Ability/2 and i think you might prefer the same, gets unbalanced with books on Arts otherwise.
While i use Art Lib. in my houserules as well, i dont let it decide quite so much most of the time.
Mmm, that´s a nice addition.
You realise that 0-40 would be 820 XP? And that´s what decides the write cost...
I expect he meant that things not mentioned stays as with the original rules. Then you would need 80 in an Art first to write that 0-40 book. 
It would appear so, but having an 8 in Artes Liberales isn't without cost. He's the pure academic, research for research sake, with no ability to apply what he writes about. One can read and understand concepts without being able to efficiently apply them in the field.
So using the rules, as I understand them on a character I'm running. It's Ra'am ex Bonisagus from Phoenix: Ra'am ex Bonisagus
Com +3 Creo 15, Auram 11 Artes Liberales 5, Scribe 2 and Good Teacher virtue.
He could write a 20-25 (21+22+23+24+25=115) level summa on any Art (and I presume a 5th level on any Ability?), but let's presume he'd do it on Creo, as it is his strongest Art.To do the range from 20-25 he needs to write 115 xp worth of information. His skills allow him to write (5+2)*2=14 xp per season, it would take him 9 seasons to write the book. The Quality is where the Art or skill in question comes int play, which in this case it would be 5 (AL) +3 (Mag of Cr) +3 (com) +3 (Virtue)=14
I generally like this. As an academic (and perhaps one who teaches, too?) you should know that one often knows more than they actually end up teaching. Being able to write in excess of one's skill isn't really possible, so it should be limited to the ability/Art in question. Or maybe not, the ability/Art score could represent the capability to implement said knowledge in the field under stressful conditions, something that the academic researcher doesn't usually contemplate. I'm going to ruminate on this for a while.
And it means you need an Artes Liberales of 8, too! Which requires an 180 xp expenditure...
But yes, there's some clarity necessary to this. Being able to write in excess of one's Art or ability seems off...
Direwolf: if it's possible, then someone will do it. In fact, I have a NPC who has 13 in AL and 8 in language and profession scribe (as well as bookbinder and illustrator). BUt his arts are at 5. Hence my questions, I was pushing the author to see what can or not be done.
HIs treatment of this subject is interesting.
Based on my understanding on the rules as he's written them, the NPC could write it very quickly. He could write (AL+scribe)*2, (8+8)*2=32 xp per season. His quality is at least 9 (AL 8 +1 for magnitude), plus his com plus any virtues... So, he could crank out a summa of L18Q9 in six seasons. Something's not working for me on this. I'm not against it, but like I said, I think there are some fundamental issues. On the other hand, I like the ability to write to the score of one's Art or ability.
Thank you for a lot of interesting input. Some clarifying.
Precisely. It's too easy. OR, you already know the concepts, or you know other types of concepts/traditions that are better. A more skilled magus will flicker through the books and say: "nah/meh/tehlolz"
My philosophy when designing the house rule was that A Magus with Ignem 35 would have nothing to learn from ANY form of tractatus of an CrIg 5-spell? Why? Because that was something that the magus could do in his sleep when he was an young apprentice. It's like trying to impress Gordon Ramsey with your own special recepy of boiling eggs.
Yes. Its all good. How long does it take for one person to learn EB? How long does it take to write?
The original rules are (IMHO) a little bit optimistic about how quick you can make orginial text. Also. A 39-40 book is 40 xp. It represents 4-6 seasons of high end research whith huge amounts of Vis. I do not find it strange that it translated in to books, will take about 4 volumes.
[BUT most importantly. Given the philosophy of Reveresed detailing; This "books" can be anything: Maybe its four articles of hypothetical spells and one giant index. Maybe its ten volumes of the travelogue "Dances with Vulcanos". Maybe it is a small elaborate cube with layers upon layers of writing, impossible to open if you have a MT score of less than 7. Summa and Tractates is (imho) an inhibiting way of creating the wonders and marvels of a hermetic library.]
Post Script for GMs
Also. Think of all new intricate (as in fun) problems this causes for players. Imagine your spring covenant stumbles upon the Masterpiece of Mentem by Tremere himself. Say that the score is 45-50. The characters (and players) know the have stumbled upon a priceless collection of books. Problem is, they initially don't know how powerful it is (to low MT scores), and when they know - how will they reach 45 in Mentem? Maybe they will get there in 80 years. Are the books supposed to collect dust for that time? They should be able to profit from it, but how? Who can they trust? Maybe it's just easiest to give it to Coeris and have a huge boon from Tremere. But what if the mages hate house Tremere?
Or give them a starting covenant with superb 15-25 books in all arts and watch them eagerly collect Vis and blowing them selfs up in the lab.
//erik. I'm sure I missed some important questions. Please remind me and I will happily answer.
Oh.
The whole add-your-magitude-to-the-quality-thingiee is because I figured that it's somewhat (not much) easier for a higher skilled person to know (in hindsight) what is important.
//erik. at least from my own experience as a lecturer.
Couple of problems with this philisophically. One, you can always learn something new, no matter how deep your knowledge of the subject is. Perhaps it attacks a problem in a new and novel way. Say a Perdo tractatus that attempts to show you 10 different ways of mimickingn an effect achievable through other Techniques. A master of Perdo might find that very attractive, if he hadn't written it himself.
Secondly, your Ramsey analogy is flawed. He is almost always impressed with people who can cook simple food well, and this is borne out by Master Chef. IIRC, his standard test to new chefs (not on competition shows) is to test their ability to make scrambled eggs. It's a pretty simple dish, and it can be easily ruined or not cooked to his standards. That establishes a base line for him. Additionally, I've seen contestants on his shows cook things very well and he asks detailed questions about how they prepared something. To think he hasn't learned something from the exchange is unlikely. He may not learn much, but he's added yet another technique to his vast repitoire. This is what I think tractatus represent in game terms.
While one can always learn something new, I don't think it follows that one can always learn something new from any given neophyte, nor that the amount that you learn is independent of how much you already know. Those are the two largest issues I take with the RAW book rules: the notion that someone with Cr1 but great communication can write a tractatus on Cr that every high-end Cr master is going to want to read. They don't want to read it because of the great insights that the neophyte has, but the clarity with which he writes. That detachment of the author's ability from the resulting text strikes me as going too far, and leads pretty directly to many of the book-prevalence arguments that are so popular on this board.
IMS, I mitigate this slightly with a house rule: Tractatii have levels, just like summae. If you are below or equal to that level, you get the full value of it. If you are above it, the quality of the book when you read it is:
Quality * author's score/your score.
Thus, the early elementary texts of even the best authors tend to be of less interest to masters, who prefer the writings of brilliant journeymen or (more average) other masters.
In my experience, both professionally and academically, I've learned from people who know less about a given subject area than I do. I may not learn much, but I do learn something. It may be that they have a different perspective about the subject matter than I do, causing me to re-evaluate something.
Case in point, heated Ars rules discussions: have you ever learned that you're doing something IYS that expressly violates the RAW? Yes, the likliehood of it happening is less over time, but it is still possible.
As ndkid said. Sure you can learn from neophytes. But it's from 1 of 100. That could (or is?) just as well be experience from exposure from hundreds of small encounters.
Learning another way of boiling your egg is not going to make you any better in what ever Creo Food lvl 40 dish you are making.
//erik. I realize learning IS a complex thing. For me the main function of this house rule is to have one formula instead of two, and to make summae closer to how you really would write a larger volumes of textbooks for medieval academics.
Except you DONT write tractatus about spells but about an Art or Ability. IIRC, you´re mixing up with a 4th edition book rule.
If it covers something simple that "you" have never dealt with before, it should benefit you.
Uargh... Step by step books... NOT fun in my opinion. Extremely NOT fun, and not at all realistic in most subjects either.
Of previous houserules similar to this, i like the ideas around Comprehension level much better, where you get MAX XP only in the correct range, but you get some regardless, how many depending on which version you like best...
:mrgreen:
Yup, made use of that myself. It´s a very nice addition overall.
Well, you can write about Spell Mastery on a given spell.
Myself, after earlier discussion about this have pretty much adopted a similar version.
A level 10 tract, if you have level 11-20 you get half the XP, if you have 21-30 you get 1/3 and so on.
It´s kinda funny, i´ve simply added more variants, each with different formulas rather than try to have one covering all...
Yes but i REALLY dont think that´s what he´s referring to.
He did mention Abilities, it's an ability. You split hairs on his meaning, I split hairs on your meaning. 
I don't think learning is a linear experience. You don't learn bits 1 2 3 4 5, then bits 6 7 8 9 10. Moreover, maybe the bit you learned is merely that 5 other bits exist and you can learn them when you need them.
Even if you know all the bits in the tractatus, maybe you never connected them together and saw how the overall picture formed more bits. Most real-world example of tractatus are readable in a week or so, if it takes a whole season it must be because you have to form your own insight into the work. And why should your insights be the same as the next reader?
If you believe a lowbie tractatus can never teach anything to a experienced reader, you are falling into that linear trap. Even a master at Animal might have never studied owls, maybe the bits he hears have little value but it might make other bits click together.