Lets say you’re trying to counter a spell that is being MuVi’ed into a different spells. For arguments sake lets say it’s a InVi spell being changed into a CrIg spell and you’re trying to fast cast a defense. Which spell are you countering, the InVi, the CrIg, the MuVi, any one? The rules say a fast cast defense of half the level is enough to protect the maga, deflecting the spell, and a fast cast defense that exceeds the level of the spell completely neutralizes it.
I think a full defense or a half defense on either the original InVi or the changed CrIg spell would simply stop the spell. A full defense on the MuVi would leave the original InVi spell cast.
Would a half defense on the MuVi ‘deflect’ the spell so it doesn’t target the original InVi spell?
On a side note. The book doesn’t say what you’re casting. I’m assuming it’s PeVi or PeForm, which ever is stronger but it’d be nice to have an actual explination or whats happeneing aside from the strict mechanics. .
There is another alternative: if your own spell is about to be changed, you can always interrupt your casting. If your spell is not cast, it cannot be modified.
The spell you want to counter. There may be some troupe discussion as to whether you’re allowed to counter the CrIg spell because there is some ambiguity as to whether you can correctly interpret the form of a spell radically changed by MuVi into another TeFo.
The fast-cast defense is fluid enough to be able to use most arts, but the chosen combination has to make sense in the context. PeVi and PeForm tend to always make sense, but using CrAn to conjure a cow between you and an incoming Crystal Dart is something that I would allow, much like I would allow other Creo spell, mutoing the air into something solid, mutoing the target of a spell into an invalid target, and so on. On the other hand, there are art combinations which are hard to justify - Mentem tends to need to penetrate, Ignem doesn’t really block a Terram attack, etc. I see the targets as rough estimates of what you need to roll to avoid having to look up every guidelines the way you would if you were gauging a spell. And I use the type of art used in counter spell to describe what happens and gauge any side effect of spell deflection… Perdo Vim tends to have no side effects.
Would be living in the 19th century when pure magnesium was actually isolated? In Mythic Europe we’re dealing with “magnesia” which was probably magnetite (natural magnet) or maybe either magnesium carbonate or manganese dioxide.
The literalism wasn’t the point. Realisticallt magnesium in Ars Magica is just metal with a highly unussual property (burns brightly when ignited) which MuTe can easilly accomplish. The real point is that you cannot categorically say that Ig cannot block Te is to ignore all kinds of possibilities, especially when in some contexts Te includes ice as an inorganic solid. Similarly PeIg on many forms of Te will make it more brittle. Heck one of the most primitive forms of mining as flame setting, using fire to break down and erode rocks that were too hard to attack with a copper pick.