Thus far, I've only had my players dealing with books and tomes related to only one art or ability.
I've seen plenty of published books out there that act as summae or tractati of multiple arts or abilities.
I realize that a book solely on IGNEM with a quality of 8 nets a player with 8 experience points towards that ability for a season of reading, but what about the others?
A player finds a hefty tome that is a Summa is Magic Theory (Level 6 quality 5), and a summa of Ignem (level 7, quality 5). Does a season of reading this tome grant 5 exp in both Magic theory AND ignem, or does the reader have to choose which gain he takes?
For as long as we've been playing, you'd think I should know this by now, but I've looked the Long-term events chapter over twice without finding a real answer.
It is 2 books in a single tome. You have to choose which one you read. It is 2 summas, after all. You can only read 1 suma per season, so there you go (I also think that is a questionable simplification, but it is how the system is designed and... it works! Quite fine, actually. After tinkering quite a bit with the system I have my preferences* but IMS books are played as per the RAW and they work fine when it comes to advancement et al.
I fail to see why a rules issue is a silly in game question
= My preferences are about using only tractati and puting a 15 points limit to the amount of tractati you can read per season; a summa is a collection of tractati. No level anymore, only quality matters. Quality is 6+com + modifiers from covenants. Roughly it would be that Most books are quality 9-10 or so. It was declared "non kosher" by my buddies, so it fell to the sidewalk. I still think it is a neat idea to simplify the issue, but hey.
I don't think there is an official rule on the subject, so you would have to decide for your saga. I personally like the idea that a compilation tome, when read, would randomly give you a bit of both for the one season of study. As in your example of Magic Theory and Ignem, the reader would get 5 experience points total, and the allocation between the two subjects are given at random. This gives me the feel when reading through a book that covers two subjects, linking them together, you get knowledge in both at the same time, and you don't know what you will get when you sit down and study it for a season.
In a single season, you can only get experience points for a single source. Each different summa or tractatus represents a single source. A single book can contain multiple summa and/or tractatii but since you can only gain experience points from one source, you can only get benefit from one of the summa and/or tractatii contained in the book.
I can see perfectly logical arguments for both YES and NO.
I see what Lucius is saying, and I see wisdom in it, but my counter-argument would be due to the rules text organization in the 5th edition book. Under the advancement section, the headings that actually serve as sources are: EXPOSURE, ADVENTURE, PRACTICE, TRAINING, TEACHING, BOOKS, and VIS.
Yet, as a counter-argument to that, a tractatus and a summa could have different source qualities, therefore a different "source" of advancement.
Considering the present Ars Magica campaign I'm running (my most successful to date, as people other than my players are beginning to show up JUST to hear the story in real time!) is "unorthodox," full of house rules, each player is a magus, extra stuff you can do with confidence points, and injecting a little extra "high fantasy" into Mythic Europe...top that off with the fact that I gave all players "Mythic Blood" for free...I'd say that the option for allowing reasonable multi-advancement from a single book is not uncalled for.
In a standard Ars game, I'd rule on the side of those who say you have to choose.
I think, for right now, at least, I'm going to allow the multi-advancement option. We play a very slow-moving (time-progression-wise) game...and the players absolutely love it. I've kept all of them balanced with each other, and I've always found suitable challenges for them.
I'd still love to know one of the writers' opinions, but thanks everyone for your input! 8)
Usually when I design multi-subject books, I require the student to split xp's between the topics. For example, lets us say that a codex contains a L4 Q8 Parma Magica Summa, combined with a L5 Q10 Penetration Summa. You gain 4xps in Parma and 5 in Penetration. If you have the Booklearner Virtue, you split the bonus too for another 1Â½ xps in each subject (I keep track of half points for experience).
The authors tend to go out of their way to leave many of these issue undefined. Some have preferences, almost all have house rules and personal interpretations, but most equally advocate no single "right" or "wrong", except for each individual SG or Troupe.
That is the bottom line.
Then it's time to look beyond mere logic. Think of what it will do to/for your game.
And MM has done just that.
Anything else opens the door to huge abuses. Imagine the ultimate apprentice summa, all 15 Arts in one tome, Level 5, Qual 15 in each - hey, that's gotta be pretty easy to write... And how is that book different from reading 15 summa of Level 5, Qual 15? In my opinion, only in the munch factor.
So long as they do not upset the balance of your game, multi-topic texts are fine. But they should be the exception, not the rule, and handled carefully, and with an eye how they make sense vs the norm.
AM tends to be a slow-advancement game, focusing on the long storyline more than the character's development, especially considering that "seasons" pass. In certain other games, it's quite possible to go from novice to thug in a week's adventure - stomp a few orcs, take their treasure, then ogres, then a dragon - hey, woohoo! But in Ars, one game session, unless it's book-keeping of several/many years of advancement, is unlikely to see any huge changes. Players should savour the small advancements - and a book like what you're talking about could make the usual advancement even more frustrating.
Note that, as far as I know, there aren't any rules covering writing multi-subject books. Like other people, I merely treat them as separate books in a single package - they could just as well be separate volumes.
(For what it's worth, I do the same - you either read a book to learn A, or to learn B, not both at once.
A bit forced and artificial, but it works well with the RAW - and remember, it is designed as a balanced game, not a RL simulation. RL would be far too complex to model, so I suggest not even going there.)