What is the average Tractatus Quality?

You still missunderstand i'm afraid. Communciation DOES NOT stack with essential virtue. Assuming your com is 0 or higher you use either your com score OR your essential virtue score to calculate the quality. This gives a maximum quality of 18.

I'll illustrate how the virtue works with an example. We'll use covenant rules so quality of the tractatus will be:
author's communication + 3 + 3 (for skilled professionals) + 3 (good teacher) + 3 (resonant materials + clarification)
We have four magi with different communication scores, they all have access to professionals, have the good teacher virtue and will use story aquired resonant materias and clarification. This will give a quality of: author's communication +12.
Person A has +5 com
Person B has +2 com
Person C has 0 com
Person D has -1 com

If they don't have the essential virtue they will write tractatus with the following quality:
A: Q17 (5+12)
B: Q14 (2+12)
C: Q12 (0+12)
D: Q11 (-1+12)

If they have the minor essential virtue they will write with this quality:
A: Q17 (5+12)
B: Q15 (3+12)
C: Q15 (3+12)
D: Q14 (-1+3+12)

If they have the major virtue they will write with this quality:
A: Q18 (6+12)
B: Q18 (6+12)
C: Q18 (6+12)
D: Q17 (-1+6+12)

As you can see the major virtue provides only a small benifit for the person with +5 com and the minor virtue provides no bonus at all. The guy with -1 com will always write at a lesser quality since a negative stat have a negative impact on the virtue. Major virtue + good teacher costs 4 virtue points and let's you write at max of Q18. If you sacrifice other stats you can write at Q17 for 3 virtue points while also being great anything else related to communication (or for 5 points if you don't want to sacrifice other stats which is a reasonable trade-off). Like i said earlier, essential virtue is far from overpowered and it's only for when you have a very specific character in mind. In fact, if you want to limit the quality of books in your saga good teacher is the first virtue you need to get rid of and not essential virtue.

Hopefully this will clear everything up regarding this virtue. :wink:

I get it. I was relying upon Lamech's understanding as he had presented it elsewhere. All that being said, I still don't like the virtue applying to writing, but at least I understand, were it applied to writing, the impact isn't as great as I had understood.

GHAA! If I presented it as stacking with Com, that's my bad. It does NOT stack with com. (Unless com is negative). Its not any better than com+6. You can use inner heartbeast mysteries and rituals to get that high. And in all honesty getting a resonance beyond +1 is going to take work. So that's 6+6+3+1=Q16 You could get better with a story, but... you could also dredge up the ghost of an archmage, or study from a post-Becoming Merinita if you are going to bother with that. The people who make them, unless they happen to be really nice, will probably try to keep fairly tight control so they can get the most from selling them.

Unless the PC is making it this is seriously expensive, or special favour territory. (Also if the PC makes it, I won't complain. I fully support team work.)

Because of the way the traits work you don't have to put any points in the stat so in addition to performing better in it's bailiwick a Major Essential Virtue is slightly cheaper then raising a stat to +5. The extra points can be used for sharpening a character's focus or branching out.

They can also be good for creating characters who are substandard except in specific cases. Clumsy archers, Dim magi who are almost savants at spontaneous magic, An overweight knight who gets winded climbing stairs but can still soak up damage like crazy.

Reread the section. Essential traits replace the Com score. They do not stack. Faerie Sympathies do stack, but with an ability, not a characteristic. Major writer +6 gives you a Com score of 6 for writing books.