Likewise, the major Hermetic virtue Secondary Insight also gives you secondary XP in other Arts, but does not appear to change totals during character creation.
Actually, I am not even clear if Secondary Insight gives the bonus to the same Arts every time, or you get to choose which Arts get the bonus each time you get XP.
Secondary Insight is a virtue that needs to be rewritten in a way similar to Elemental Magic. However, I think David Chart ran out of time in the last round of errata to fix it properly.
I have time now. The Virtue appears massively underpowered for a Major Virtue. We should probably buff it to look more like the new version of Elementalist.
Do people have specific ideas of what it should look like, and what needs to be clarified? And are there any other problems?
I will come up with a proposal once we have agreed on the shape of the problem.
I have always been unclear if you choose the Arts that get secondary advancement at character creation, or each time Advancement points are put into an Art.
My reading has always been that you get to choose anew each time you study an Art.
One could certainly just scale up Secondary Insight like has been done for Elemental Magic.
But it feels just a bit too bland for a Major Hermetic Virtue. Just a bunch of extra xp without any kind of theme or anything.
While mechanically Elemental Magic is also mostly a bunch of extra xp, it has a lot more flavor.
My opinion is that Secondary Insight as written would make a good Minor virtue. A bit on the strong side, but not overly so I think.
Or one could rewrite it significantly to change it into a suitable Major virtue, but that would essentially be a new virtue, and I am not sure what it would look like.
You're not entirely wrong. Often, book learner is more powerful, because while it's restricted to books alone, so long as you don't run out of tractatus to buy, it isn't a problem and you can benefit in your non-hermetic studies too. The one problem with this approach is it would leave Study Bonus in the dust. But Secondary Insight as written as a Minor virtue, and Study Bonus getting 3 xp instead of 2, would balance out fairly well with Book Learner. The alternative is, as you say, buffing it so it's worth a Major virtue.
Study Bonus and Book Learner also have the minor advantage compared to Secondary Insight in that the extra xp is for the Art you study - which is presumably the Art you are most interested in raising at that time.
Fair comment.
I think secondary insight is (just) slightly to powerful for a minor virtue. You can advance your primary form/technique every time you read any form/technique. Once upon a time I suggested that, as a minor virtue, it would always add xp to the forms/techniques with the lowest score.
Not that I am as convinced as I was.
Just throwing out ideas here: What if it were minor, but the additional XP had to go into abilities that one already had a score in?
Secondary Insight as a Major Virtue, in my opinion, should look something like this:
Secondary Insight
You see some connection between all Hermetic Arts, and when studying one of them, can glean insights into others you are less versed in. Whenever you gain experience from a source dedicated to one Art, you gain one third the Source Quality in experience points in your lowest three Arts, other than the one you're studying. In case of a tie, you can choose which gets the extra XP.
For example, if you studied Creo from a book with a Source Quality of 13, you would gain 5 experience points in each of your three lowest Arts. (This would not change if, for example, you also had Affinity with Creo.)
As it stands, I think that Secondary Insight is vastly underpowered but clear. I had never thought that the choice of which techniques/forms benefit from the Virtue had to be made once and for all at character creation. That would make the Virtue even weaker, and in Ars Magica the need for one-time choices tends to be explicitly spelled out.
As for re-writing it, I think the easiest (but not the best!) path is to turn Secondary Insight into a Minor Virtue. It would be neither a particularly strong, nor a particularly weak Minor Virtue. It provides a +2/+4 xp bonus each season spent learning Arts from a teacher (unlikely beyond apprenticeship), books, or raw vis. Crucially, those xp are "dispersed" into the Arts you are not studying - this is a very significant weakness in a game where being a generalist is a weakness.
Thus, I think that as written Secondary Insight is somewhat stronger than Free Study (+3xp to the Art you are studying from raw vis), but definitely weaker than Book Learner (+3xp to the Art you are studying from books, and to everything else you are studying from books) and Affinity (+50% xp to a single Art when you are learning it from any source including adventure and exposure, and also applies to starting xp).
The more difficult, but I think the most satisfying solution is to rewrite Secondary Insight as a character-defining, Major Virtue: we already have almost too many "get a few extra xps" Minor Virtues. In this case, the first step is to understand how we would like it to define a character.
It seems the original idea was to make it a good Virtue for generalist magi. Now, generalists are currently extremely underpowered. This has three consequences for a generalist-defining Major Hermetic Virtue:
a) it's a great idea that opens up a wide niche of currently unappealing character concepts
b) it has to "go big", because applying a "fair" Virtue to an unappealing concept leaves it unappealing. In this sense, a good question to ask preliminarily is the following. Consider a Te/Fo specialist with a score of, say, 30 in the specialty Technique and Form, and 5 in every other Art. Now compare it with a generalist with a score of X in every Art. What X makes the two balanced? In my opinion, X=20 is about right. But note the vast disparity in xp: the first character has 1125xp, the second has 3150xp, almost three times as many.
c) because of b), the Virtue must be carefully designed to ensure it can only be channeled into a generalist concept, or it risks producing overpowered non-generalist characters.
I have seen a number of elegant proposals for re-writing Secondary insight in this sense. A few that appear reasonably balanced or slightly underpowered to me (and that can be justified with the usual "you view all the Arts as a connected whole"):
- In any season you study generate a Study total in an Art from any source, you can forfeit any xp gain, and instead add 1xp to every Art.
- In any season you study generate a Study total in an Art from any source, you also gain 1xp in every Art that has an equal or higher score (this is a very subtle mechanic).
- Whenever you gain xp in an Art without benefiting from any other Virtue, assign the same number of xp to each of your two lowest Arts.
- Double the number of Art xp you gain from any source, including those at character creation. However, whenever you use an Art, treat its score as if was equal to that of your lowest Art.
Need to think more about it, if I can, but, for what it's worth, I kinda agree with Ezzelino here 
We should also consider the name and mechanics relationship. This may sound dumb, but if the 2 cling together, it'll both make the virtue more thematic and easier to understand at a glance.
Hum... One possibility is to tie the virtue to Magic Theory.
Increase and art => Increase MT
Increase MT => Increase an art.
This, IMO, makes sense for a secondary insight.
And this could make the virtue very good for some types (boni, verdi...)
Having Art xp boost ability xp and viceversa is nice in principle, but very tricky to execute correctly: it's easy to leave loopholes open, and if you try to shutter those down, it's easy to leave the virtue underpowered. Also, it caters to a slightly different character concept from a generalist: a magus, possibly an Art specialist, who balances Arts and abilities and will learn both even if focusing only one one of the two. The best example of this (it's a very elegant and subtle balancing mechanic) I've ever seen is Ovarwa's:
In every season you read Magic Theory, you gain 15(!)xp in arts. A story, maxing at 10xp, would yield more arts xp than one would otherwise get total.
Just observing. No point made.
Sure. It makes sense thematically, if you are best at learning through secondary insights.
From a game balance point of view, it's not really game breaking. A magus who never studies the Arts, and spends 1 season/year in the lab (developing spells, enchanting etc.) will have earned 300xp in each Art 100 years after gauntlet. Ignoring the initial xps (that make little difference) that's a score of 24 in every Art. A strong generalist with a whole lot of ability xps, but hardly game-breaking.
I think this highlights a crucial, and oft underappreciated point: not all Art xps are worth the same. In particular, xp gains that are dispersed over many Arts are far less valuable than xp gains that you can focus into 2-4 very strong Arts.
One idea that could be part of (but not all of) a re-written Secondary Insight is something to make requisites have less impact, due to seeing connections between the Arts.
For example:
When casting a spell with requisites, you may count the score double of any of the main and requisite Art scores, but not higher than the highest of the Arts, before doing the normal requisites calculations.
Example:
Shape of the Woodland Prowler is a level 25 MuCo(An) spell.
If a magus has Muto 12, Co 16, An 9 he would normally get 12+9= +21 to his casting score from Te+Fo.
With this modified Secondary Insight he would be able to count his Animal score double, but not to more than his Corpus score. So the bonus to his casting score would be 12 + 16 = +28 to his casting score.
This has the disadvantage of making generalists even less competitive with specialists. In fact, a great way to support generalists is to go the opposite way: have a Virtue that provides huge xp bonuses while making everything a requisite (i.e. anchoring you effective Art score to your lowest Art, rather than to your highest).
It does have the advantage of making certain character concepts that heavily rely on requisites (e.g. shapeshifters) more viable.
The main effect that I see is that the magus can focus on all sorts of other abilities, and still develop fairly well as a magus. One can play the political Trianoma or the army commander Tremere or the artist Jerbiton, and still advance a lot in the arts.
Sure, it won't break the game in the short run, and in the long run there are so many potential game breakers in such a high powered game as ArM. I agree there is no reason to worry about game breaking.
I don't agree, but value is relative to purpose, so I would love to hear why you value the specialist.
To me, I find that the magic specialist is a little like solving every problem with a hammer. Nail, or screw, just hammer it in. Bigger hammer, you need no saw.
While I can enjoy the narrow-scope high-power magic, I find I get quickly bored. A generalist magus gets more stage time and achieve more in a wider range of stories. Doing a lab project with a lab total well beyond a hundred may be an entertaining achievement, but additional lab projects in the same TeFo combo tends to be more of the same and fail to entertain. YMMV.
No, I am not objecting to your idea. I do find it a problem that certain concepts, typically Tremere, Trianoma, and Jerbiton, take so much attention away from magic that they do not deserve the player's magus slot. Your controversially high-powered secondary insight might be just the fix we need.