So, I've joined a new group, and am going thorugh the process of figuring out how they play Ars - one of which, of course, is arguing about the rules. 
Anyway, was under the impression that the current canon for a Minor Magical Focus was basically a TeFo - while a Major Magical Focus was functionally a Form (although both can be spread out over a number of TeFo's). The rest of that group seems to disagree. Is this not the case?
Minor Magical Focus: "In general, the field should be slightly narrower than a single Technique and Form combination, although it may include restricted areas of several such combinations." AM5 46
Major Magical Focus: "This area should be smaller than a single Art, but may be spread over several arts..." AM5 45
Emphasis added.
In other words, they are narrower than you thought.
Yeah, but "slightly smaller" technically means 9.99999 < 10. As such, I was wondering if there were any official rulings (such as official character write-ups) that have a MMF as a TeFo, or a MajorMF as a Fo.
EDIT - I was under the impression that later books clarified this, slightly.
EDIT II - also, I though I had heard that MajMF had been used as the formal "how much a Major virtues should be worth" in later books, by being roughly equivalent to 5 minor foci, or something like that. But that's hearsay, at this point.
That's way too broad. Perhaps you can present your idea for the focus and it can be adjudicated here. Although that may not work with your group.
Jonathan.Link - nah, it was mainly just us discussing rules - mainly in the context of how most Major virtues kinda weren't worth it.
I've usually interpreted "slightly less than a TeFo" to mean "up to a TeFo", simply to avoid arguments - although if you want to be technical, you could drop a single guideline and still be within RAW. Of course, figuring out a simple phrase to describe that would be a bit of a challenge. For example, I imagine "creating weather" would work for CrAu, as there area few CrAu spells that aren't actually weather - such as that one that creates healthy air around you.
Similarly, I've interpreted "less than an Art" (Form, really) to mean "slightly less than an Art" - so basically 9/10 of an art would be valid, if you could figure out a way to phrase it in such a way that wasn't just silly.
But that starts to get into the whole "well, what if my focus just happens to match up with a Form?" - as it's not unreasonable to say that someone focuses on Plants, or Animals, or Vim. (ie, those do seem to be meaningful categories.) Thus you start to get into the difference between "less than a Form", "just a little bit less than a form", and "a form".
But again - I thought there was a later clarification that addressed this, if only slightly.
Well, Animal and Herbam also include thinks made of animal and Herbam Products, so a focus on Animals, probably doesn't affect those things that aren't actual animals. Similarly with Plants, it has to be a plant, not a plant product.
It's not really hard to find spells that don't fit within a focus. I have a maga with a weather focus, there are very many Auram spells that aren't in her focus. Of course, there are a lot that are. I disagree that the major virtues aren't "worth it."
From the examples given and the way we play MMF:
A minor focus could be up to half the legitimate spells of a single TeFo combination, but not typically more than that. For example, 'creating fire' would be a valid minor focus. It covers about half (well, a little less) of the Creo Ignem TeFo combination. It doesn't touch the creation of light or heat, which excludes some CrIg spells and effects.
A minor focus could also be a small percentage of an entire form, but we're talking a small percentage. For instance, a minor focus in Wolves would affect any Animal spell cast on a wolf. Wolves is a tiny fraction of the Animal form, but in this case it hits everything from creating a wolf to harming a wolf to controlling a wolf.
A major focus could be up to half the legitimate spells of a single form. For example, 'fire' with Ignem. It's big and broad, but it still excludes heat and light. This means the focus won't help with things like PeIg cold spells, or MuIg light-related trickery.
A major focus could also be the equivalent of a minor virtue across a number of forms, such as Necromancy or Elemental Spirits. Each of these could be seen as a combination of minor foci across a group of forms.
And yes, Magical Foci are absolutely worth it. To the extent that they cast a huge rules-shadow across the entire game.
I'm creating a Bjornaer with the Wolf of Virtue Mythic Blood (HoH:MC page 37) which gives me the minor magical focus with wolves. In which of the following cases can I use the bonus?
I guess number 3 doesn't apply, and thus I should make a wolf-specific version of those spells in order to take advantage of the bonus.
And another question: can I apply the MMF when choosing the spells during character creation?
Thank you!
What happens at your table trumps the rules, though. The answer literally doesn't matter in your particular case.
The game's meant to be very play-contracty like that.
As a suggestion: if the spell specifically targets wolves in the design (item 1) then mmf applies, otherwise maybe not by circumstance.
If casting a spell on a relevant target and only that target, then the mmf applies. If a spell happens to affect a wolf it shouldn't apply. In example 3 I'd suggest the Speak with Animals applies the mmf but the ward does not.
And yes, a wolf specific ward would use mmf.
Lastly a spell cast on yourself in wolf form isn't automatically going to include your mmf.
Although that does suggest a cheesy workaround using Shapeshifter virtue. "Why, yes. I AM a wolf currently, thank you."
Although to be fair, that means you just spent four Virtue points to get "self" as a MajMF.
Ha! Yup. It counts for wolf form from MuCo spells too and I'd be happy to allow that even though is a little bit of a rort. More like rewarding lateral thinking imho.
All three cases apply for casting the spell, provided the target meets the criteria of wolf.
For lab-work, however, only the first one benefits from the focus. 'Shape of the Woodland Prowler' is specifically relating to wolves, so the focus would apply for lab work. The other two scenarios are regarding spells that aren't exclusively wolf-y, so no lab benefit would apply.
Note that the lab benefit applies for any effect that you are designing that is fairly explicitly about wolves (e.g. summon a wolf), but also applies to any effect invested into a wolf. While not relevant for Bjornaer magi, this can be leveraged for familiars that match magical foci for other houses.
Would "Mercurian Magic" be a minor or major magical focus?
Depends what you want it to cover. If it covers all rituals, then I'd say its too broad for a minor magical focus. I could see some kind of focus relating to casting spells in groups using wizards communion but I'd prefer to use special circumstances for that as it seems to more closely match the mechanics.
Timothy's answer "What happens at your table trumps the rules, though." is of course the whole of it. The rest of us are left with discussion about specifics for the joy of discussion.
So, taking in mind that it doesn't matter what we say, we can look at the lists of examples on pages 45 and 46 of the core book.
They all look pretty good to me, (with the exceptions of the minor focuses for herbam; fruiting and wood those strike me as too small and too large respectively).
the majors: (women's bodies, salt water, trees, domesticated animals, metals) look to me like they cover a significant portion of a form - up to half of one.
the minors: (birds of prey. small steams, disease,erasing memories, the color blue) are pretty darn specific. while "erasing memories" doesn't come close to a whole technique/form combination the examples like canines can be used for every technique and form.
I imagine the intent of the rules runs like this: "imagine the set of all possible spells now imagine the fraction of this set that your focus applies to. A major focus should be about a quarter the size of a form (~2% of all spells) a minor should be about a quarter of a technique/form combination about 0.5%, but obviously you should choose things that will contribute to cool stores and not worry so much about individual power." (I also imagine this as a physical personification of the rules sitting in a comfy chair with a glass of brandy actually saying it followed by "yeah, that's what I was thinking,..huh... can you get me a refill?")
In my experience there comes a point in play after a few decades of game time (so irrelevant for all but a few of the sagas in which I've played) where any minor magical focus that involves a physical object becomes more valuable then any non-physical focus major or minor. In other words a minor focus in left handed asthmatic pinkish tree frogs is more useful than a focus in visual images, emotions, or disguise. This is because the maga of sinister wheezing rosy tree frogs will have spells to conjure up as many of them as needed and other spells to use them to accomplish most anything that she needs done (manual labor, building material, communication, combat, retrieving information, what have you) the master of emotions is going to find it a greater challenge to apply their focus to as many different problems.
The book assumes that the important issue is what proportion of the world that surrounds that magus their focus applies to. In doing so it misses the fact that magi are capable of filling their environment with any arbitrarily large quantity of their focus.