I'm not even sure if I'm correct. It seems like if fast-cast MuVi could affect an opponent's casting (and it can by the guidelines box) and could seemingly potentially so with a non-Form-specific spell since that box seems to apply in general, then PeVi ought to be able to, too. I just can't reconcile those with the statement about needing to know the Form.
I'm ready for AM6. /5
No, I had started with only thinking of Hermetic Magi.
I see, other Traditions and Realms makes the Awareness roll more difficult, and may upset the choice of counterspell.
It's always a little shocking to see such disagreements over basic core mechanics after dozens of supplements and expansions have been published.
Personally, I can't see any form of magic being more appropriate for counter spelling that PeVi. I'd assume that the text in the corebook about needing to know the form of the incoming magic applies to basic counter spelling, not generalized PeVi.
And more than 10 years!
I would tend to agree with you on principle here.
Plus, I still cannot get the MuVi rule block and the statement about needing to know the Form to reconcile. Yes, some MuVi spells don't need to be Form-specific, seemingly the ones that don't change Range/Target/Duration/Base/Arts/size/etc. However, not all MuVi need be Form-specific, seemingly the ones that alter the stuff not written into the spell, like the sigil. And if MuVi is an exception to that one statement in this regard, I can't see why general PeVi spells wouldn't be as well.
If you want to counterspell without knowing the Form with a PeVi, I would infer from the core PeVi guidlines that if possible, it needs to be more difficult than a normal counterspell (since dispelling is four magnitudes easier if you target a specific type such as "Hermetic Terram magic" rather than "any magical effect"). Something like matching the level of the spell disrupted would seem about right.
While I disagree with the math, I see what you're getting at. The rules for countering that say you need to know the Form also say you need to use roughly half the level of the effect. Meanwhile, non-Form-specific PeVi works off being roughly double the level of Form-specific PeVi. Without the restriction of knowing the Form, you lack that benefit and so much use a much more powerful spell. I'd buy that argument. I feel like it keeps a fairly consistent interpretation between the countering rules and the PeVi rules.
MuVi Guidelines says explicitly that you can cast on spells cast by another magus either cooperating or fast casting the spell, so yes you can.
But you have to fast cast, do it at R: Voice, with the duration of at least the target spell's, never after the target spell had been completely cast, beat target spell's penetration with your fast casting, and as it also says "All Muto Vim spells require some tailoring to the specific use", I guess that either you have a bunch of mastered counterspells already designed for frequent spells and get lucky getting one of these, or you definetively will need to to all that stuff with spontaneous magic, and being it spontaneous.
And after that, Muto Vim effects make changes on spells, either superficial, which doesn't seem enough for any effective defense, significant or total. As only total changes can alter either Technique or Form, I wouldn't ask for a roll to determine the arts if doing only the Mu-Vi-Significant-Change-Defense of, lets say, changing the target of that incoming Ball of Abysal Fire from me to that beautiful rock over there. But I would require the exact same roll to determine the spell parameters properly (the target), maybe with a reduced dificulty if the target is pretty obvious (like a Flambeau standing in front of you, grinning and screaming that you are going to burn like a torch soaked in oil), or make the magus guess it on the fly and add him some botch dice in return. Considering it all I would say that the MuVi defense is probably doable but pretty hard to achieve unless you are a MuVi spontaneous specialist. Considering all these troubles within the Vim defense, I would definetively let it get ridden of the Form requisite.
I agree. I consider changing the target (not Target) to not be changing anything of the essence of the spell, like changing the sigil. So I think that works without being Form-specific.
Yes, it might well be, though Flawless Magic plus a retargeting MuVi formulaic spell is probably more effective than even such a specialist with an appropriate Focus. More importantly, it's impossible against non-Hermetic magic, and in many sagas that's commonly the most important stuff to counter.
Indeed, you would end with a highly specialiced magus which have nothing to do against any nasty creature power...
But I just ended editing that post above and thought of another way of defend yourself against spells while not being limited to work as a Quaesitor bodyguard: a Glamour specialized Merinita! Ball of Abysal Music points a pretty good way to counter rival spells. And to be good with Glamour will definetively be more versatile than to be a MuVi specialist.
That is the pre-errata rule. The rule was edited because of some other complications. The rule is now that the duration must last through the casting, for which Momentary should be enough in a combat setting.
Sorry, my mistake, I never really looked to the errata corrections (and it seems I shoud). Anyway, sounds good. MuVi countering is hard enough wihtout needing the duration extended.
Just a note about changing a MuVi spell to effect another spell.
I don't think that MuVi have to be spontaneous, you can have them as formulaic. The text mentions that MuVi can't be put into items, because items do a spell exactly the same every time. Formulaic magic is different. Each time you cast a spell, there are many tiny variations in it. Formulaic MuVi spells work on spells as they are cast. This is directly implied by the rules in the MuVi section.
It occurs to me that this could make magical combat much more interesting and balanced between attack and defense. The attacker would have to choose between a powerful spell, which could only be countered if the Form is successfully detected but which will have trouble penetrating Parma, or a weak spell, which can be countered by general PeVi but which will have more penetration behind it.
Anything that reduces the effectiveness of the "death by 1000 cuts" strategy of pinprick penetrations is good in my mind.
For counter spelling you really can't beat mastered formulaic spells (with fast cast ability) designed for the job. Muto Vim can change the target of the spell, including turning it back on the caster, Perdo vim can dissipate the spell before it takes effect, and you can use all the other forms for tailored defences such as creating walls to intercept oncoming magic projectiles, teleporting oneself out of the way of danger and so on.