Flawless Magic + Affinity with Spell Mastery

I would like to ask your ruling in the following case:

The character has the Flawless Magic Virtue and by Ars Goetia Binding he bound the spirit of a former magus. The former magus had the Mastery of Pilum of Fire - as one of his signature spells.

How would you calculate the XP when the character puts 5 XP of practice into the Mastery ability - Pilum of Fire ?

FM doubles the amount of XP and the bound spirit gives you an Affinity. Would both of the modifier be valid?

My gut feeling is no.

  1. I would not normally allow affinities with spell mastery; take flawless magic instead.
  2. Ars Goetia says that the magus can take XP as if they have an affinity; there is no suggestion that they get an affinity on top of what they already have. If they already had an affinity, they also get XP «as if».

Thus, if you allow a character to take flawless magic and a cumulative affinity on top, the answer has to be yes. Otherwise, no. I don't think Ars Goetia changes anything here.

Binding specifically calls out Affinity for Abilities the spirit and the person share, and since Mastery is treated as an Ability, it should RAW, benefit from this.
Whether it would, in a given troupe, is a different matter.

Affinity modifies the Advancement Total when studying that ability (which includes practice). Flawless Magic doubles any XP you put into the ability.

Should you have both they should apply independently of each other. I can't think of any reason why they shouldn't.

So Practice with a Source Quality of 5. Affinity applied to the Advancement Total gives 5xp x 1.5=7.5xp which rounds up to 8 xp. Finally Flawless Magic doubles this to 2 x 8xp=16xp

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I was under the impression that Spell Mastery were separate skills, one for each spell.
ie Spell Mastery for Pilum of Fire is a different skill than Spell Mastery for Palm of Flame.

In fact, since each magus invents their own version of each spell, would one maga's Spell Mastery for Pilum of Fire be a different skill than some other mage's Spell Mastery for Pilum of Fire?

Books on masteries are canon enough, so no, they have to be the same ability.