OK, cool. So a spellcaster can have any number of spells on scrolls, grimoires, spellbooks, etc. But they can only use their full specializations and masteries on the spells that they "know". Correct?
Yeah, I believe so.
But I am kind of fuzzy on how many they "know". I am clear how many are known at character creation (half of power source MRV). And when the PC levels up, she has the capacity to learn one new bonus spell plus more for new die-ranks in Specialization or Mastery? Example: A 1st level PC with Arcanum D6 > Mystical D4 would know 2 spells. When she levels up, she adds ranks to her Specialization and also gains Mastery: Arcanum D6 > Mystical D6 > Wizardry D4. So she now can know 5 (from Arcanum tree: (6 + 4) / 2) + 1 (from leveling up) = 6 spells. Correct? And all of these 4 new spells must be acquired by game-play (training, discovered scrolls, etc.), not "automatically" Correct?
Figures are correct as far as I can tell.
I would guess that you would have to choose which spells are "known" at a given time? So using the example caster above, You can know and cast 6 spells at any one time but if you had a spell book w/10 spells in it for your power source, I would guess you would have to pick which ones you "know" and which ones you could only cast from the book?
OR it could mean that the ones you "Know" you can cast always but you are stuck with them. That seems a bit extreme.
I would go with my first thought. Say that the caster has to mark which spells they can use. If they wish to switch they will have to let go of one known spell and then study/pray/meditate for the new one (Takes 10 hours or something)...SO if you had Light, Fireball, Lightening, Flying, Know Languages & Armor, You could cast them as long as you have SPs/Resilience to do so. But say you have Acid Wave in your spell book as well and that you want to be able to cast it at full strength. So you let go of Armor and spend the requisite time to study/pray/meditate to play Acid Wave in your "known" group. Just a thought.