Instead of using Sorcery in its standard BWG form, I was thinking of converting it into a “training skill” costing 2 points to open, (training skill root for aptitude only) this would allow mages to then learn to do spell casting. Each spell would advance as a seperate skill rather than all at the same time as with the current sorcery skill. Smaller obstacle spells wouldn’t be as highly skilled as the High obstacle ones, (high and low obstacles depending upon their opening root which is still half of the perception stat.) This way, the spells you cast most often have the greatest chance to advance through testing while those that are not as practiced give the greatest chance for error. This also ensures that no matter how well rehearsed even the low obstacle spells still have their risks as it is doubtful that one could get enough tests for an obstacle 2 spell to ever raise that skill higher than a B4 or B5 where success is far from guaranteed. Also, it makes wizard types choose what spells to start out with, and at what exponent level (purchasing spells with resource points still opens them up but they could then use skill points to advance individual spells in character burning) as opposed to buying Sorcery up to expert or near mastery level (B5 or B6) and taking on any new spell at that level and advancing all spell skill with one skill. Elven songs are learned and advanced on at a time, as are DoW skills, Weapon Skills, Artists Skills, Forestry, Peasant, Academic, (ect) are all learned one at a time. Why not sorcery spells? (or am I over complicating things again?)
I’m not clear how you would ever advance a spell skill using this system, since you need a mix of obstacles to advance. (I can see some corner cases like being injured allowing advancement, but it would still be a LOT harder). Also, are you thinking of making a new set of very broad spells, or the existing one? You make the comparison to Elven songs, but those are typically much broader than Sorcery spells, having a half dozen or so different effects. They are closer to other skills in that respect.
What are you hoping to get out of this system? Would it be simpler to just replace the sorcery system with elven spell songs?
It might be easier to have the basic spells associated to individual spell effects (Destructions, Alterations, Illusions, ect.) instead of the Sorcery skill. That would still cause diversity of magical skills without the spell by spell advancement problem you mentoned. I could open skills up for each discipline of magic and those skills would handle the application of their spells (Illusions for spells like “The Fear” or “Force of Will”, Destructions for spells like “Shards” or “Fire Fan”, Alterations for spells like “Mage Sight” or “Falcon Skin” and so forth.
The Sorcery Skills would have to be well defined, as would their allowable spell lists, but it might be worth trying. I would still want to have a way to improve individual spells though (maybe a die trait).
Larkin, I have been working on a hack for traditional sorcery that does exactly that - split the sorcery skill up into a handful of different sorcery skills, each of them representing a “school” of sorcery.
My intent is to make sorcerer’s advancement a little more balanced with other character types. Sorcerers have the issue that advancing a single skill (sorcery) makes them better at wide range of things, whereas advancing other skills makes you better at a (generally) much smaller range of things. A number of spells are essentially the equivalent of having an entire skill (Chameleon, Phantasmagoria, Mask, etc).
I have found that it is hard for sorcerers to acquire new spells unless things are done in the game to specifically accomodate that - they need huge chunks of downtime. If there aren’t huge chunks of downtime, sorcerers will not get new spells. This is partially a good thing, because the difficulty of getting new spells is part of what prevents sorcerers from dominating the game too much.
Anyway.
From fiddling with it, I have found that D&D style schools fits the spells in the BWG book fairly well. There are 67 spells in total and with 7 schools as there are in my current attempt, each school has wide range of obstacles and a clear theme for effects.
So far it looks like most sorcerers would want to pick up 2-3 different schools for their effects, or if they stick to one they will face some limitations on what they can do.
There are a few issues with it…
To advance a school you probably need more than one spell from that school. Sorcery is very flexible with regards to obstacle, once your skill is 4+ you can make almost any spell into a routine test and with fast-casting you can make any spell into a harder test. Almost.
Still, if all you have from the school of “Earth, Wood and Beasts” is “Shards” you will have a hard time advancing that school.
Splitting this up means spells acquisition can become easier, but how easy? I am leaning towards 25% discount on spells in burning and ½ the time required, but it’s tough to figure out.
The assumptions of the system are difficult to pin down. I can only go by my own experience from playing BW, which are fairly extensive, but still limited to games I have been in and the assumptions and practices we have.
The thematic cohesiveness of the schools varies a lot. One like the school of fire is very clear thematically - it just makes sense. Another like “the School of Eldritch Will aka the School of Random Bullshit” was a school I had to make up for the spells that I didn’t want in other schools.
Anyway, the skeleton of the system is here: https://docs.google.com/document/d/10JExP0eUJWM305CGQBoj-onE-SB4jl6mUyMCVGzSaRk/edit?usp=sharing
It is a work in progress and not edited yet, but it might be worth checking out.
As for your other point, I think small die traits or call-ons would be an excellent way to represent mastery of specific spells. A call-on for casting White Fire is quite potent. If you also create schools, different sorcery skills or something similar, it might become a bit redundant - if I have affinity for the Phantasmagoria spell, and that is my only “illusion” spell, then what is the difference between that and a general affinity for illusion spells? I know that one is wider than the other, but depending on spells on my sheet and what spells are under the same skill… the difference can be very small.
This is more or less how elven Spell Songs work.
It would be great if Sorcery had its own Lifepath Schools that would have not only the spells of that school but also, the necessary skills of that school. (Enchanters would mix craftsman and educational skills in with their Enchanting spells (makes enchanting more like the way elves and dwarfs do things). That, plus they could then earn more school specific traits.
Alex I was going for more of a elder scroll spell definition, but I think we are on similar strategies here. If I get anything decent worked up I’ll post a link. Although, I would really like to have the mages work more like Spell Songs and Skill Songs. But that would require new Lifepaths. (Wouldn’t it?)
My thoughts on individual spell advancement were that some spells just wouldn't advance very far, they are simple basic spells that just are practiced to the point of good enough and it's time to move on to bigger and better things. This not only keeps the experts and master spell casters from being overly confident with a simple Wyrd Lights spell, it mirrors how we do things in real life. Once we have the basics of how to light a candle or lighter we pretty much move on to other things and trust in the skills we have already learned to see us through.
I was also thinking that any spell used on a regular basis would advance over time just like any other practiced skill. But I’ve given up on this line of thought in favor of different dchools of thought and spell categorized by their effect rather then their components (Currently looking at Destruction, Divination, Conjuration, Alteration, and Illusion) I am also considering Alchemy as a Sorcery Skill to brew poitions, (using Herbalism to acquire plants for poition antecedents) and Enchanting for not only making items but using them as well (for actively used items like wands and spell matrix things). Restoration magic would fall under the Faithful Trait. A mage could be schooled in any type of magic that they could afford in burning or learn in play. My mage could start with Alteration, Destruction, and Illusion and then purchase Turn Aside the Blade (Alteration), Shards (Destruction), and Force of Will (Illusion). Each skill would advance separately according to how the magical forces were being shaped and used.
I meant how would it ever advance even a single point. It would seem like I could only ever roll against one obstacle, so I would have all routine checks, or all difficult, or all challenging, but not a mix of them. I suppose things like working carefully and casting while injured make it possible but it seems incredibly hard, compared to other skills which have a range of obstacles.
Yeah, if you go the spell songs route, where each individual spell is a skill, then you would need to rework the spells almost completely. Each skill needs a range of obstacles, so each spell becomes more of a handful of different effects.
How narrow and how broad the effects should be is a matter of theme and balance I suppose.
If Eldritch Shield is a skill, then you might be able to cast it at obstacle 1, 3, 5, etc, corresponding to 1, 2, 3 Ob shield or something like that. If forking and casting carefully/quickly is possible, then that’s a fine range of obstacles.
Don’t think you would require new lifepaths. I mean, it would be neat, but not required. Simply make it so that having access to the sorcery skill allows you to open a number of spells and advance them and perhaps allow sorcerers to convert resource points from sorcerous lifepaths into skill points for the sorcery skill.
You could also go somewhere in-between, make a large number of skills to replace the sorcery skill, with each individual skill having a handful of different spells as part of the skill itself, so you wouldn’t have to learn new spells as such but your skill would just gradually have more and more applications.
Sort of like this: https://docs.google.com/document/d/1fhcdnPXF2WEd9wi6Tyjpfx1RxaLCfoi9KP5hKusT1vA/edit?usp=sharing
(been in a sorcery hacking mood lately :P)
In character burning you spend resource points on reputation, affiliation, and relationship with the guild as per Gangs and Crews (page 96 B.W.G.) and either circle up the instructor you need to learn new spells and or school of magic from or just buy that relationship at the start. (In my previous example I could spend 32 resource points to have a reputation as a guild mage, an affiliation with my local guild hall and a relationship with each of my three instructors: Alterations, Destructions, and Illusions. I could then seek out my teachers for further training, advice, and recomendations to other guild halls. If I wanted to become truly invested in the guild, I could also buy property as my rooms at my guild hall, as well as a work shop to represent my access to the enchanting and poition making labs within my guild hall (this provides resource dice and could possibly raise your circle exponent if the property and relationships cost you 50 resource points or more in character burning. The reputation and affiliation cost 17 resource points plus whatever you spend on property). I like the guild option as it provides a great spring board for quests, a way to find/learn new spells as well as teachers, and a reason for mages to adventure in the first place (Guild Dues/Guild Tax). I would use this with or without the alternative Sorcey skills we’ve discussed.
Well… under traditional sorcery you would be left with a sorcerer who couldn’t really do magic. Of course with enchanting that might not be a problem 
Still, the sorcerous lifepaths have such a high number of resource points exactly because sorcerers tend to spend resource points on spells. A lot of resource points. I did not intend to replace all the resource points of the lifepaths with sorcery skill points, just part of them. Without spells costing resource points there is no reason for the sorcerer lifepath to have an obscene 32 resource points
Ymmv and all that, but the difficulty of acquiring new spells (unless in a campaign designed with sorcerers and downtime specifically in mind) always made my players and I spend almost all their resource points on spells. Also, spells are just awesome and neat 
My first wizard burn was a four lifepath noble mage with 89 resource points, I think I spent around 30 on spells, 28 on gear, and the rest on reputation, affiliation, relationship, and property. (B3 Resource)
WOW!
My memory was a tad off on that, (it was 2D Resource plus 1D Cash). Less “wow” but not too bad. (My biggest mistake was the B4 Sorcerer trying to cast Obstacle 4 spells (at least he got a test, and a Zombie, then a ghost, then a garbled.)
I have since learned to vary my spells to skill exponent, skill exponent -1, skill exponent -2.
That combination seems to let a mage aquire game legitimate testing for quite some time as his spells get easier he still can challenge himself by casting quickly or downgrade a test by casting carefully. This also alters the Fort test for Tax.