This is for Arcane Magic and I will cover Divine Magic in the next post. Remember I am adapting the spell list found in the d20 SRD including the spell levels. For the arts of magic see this post. I am still working on the list of spells and when that done I will post a list of what spells goes into which art.
In a Nutshell
The character can cast any spell found in his spellbook with a Thaumatology roll. The higher the spell level is the more difficult the spell is to cast. Casting is fatiguing and repeated casting without rest will cause the character to pass out. A spell can be cast as a longer ritual without fatigue. Casting spells also require the expenditure of components. Spontaneous magic is more flexible and doesn't require spell books. Learning magic and spell casting are more difficult.
With the right aspect a mage can cast a spell as a single combat action. Casting requires a successful Thaumatology roll based on the difficulty of the spell. Casting is fatiguing unless a critical success or a high degree of success is rolled.
To successfully cast a spell, the result of a Thaumatology roll needs to be equal to or greater than the spell level plus one.
In order to successfully cast a spell, components costing 10d times the spell level squared are consumed. One pound of spell components equals 100d.
The casting of spells from memory is fatiguing. Unless there is a +8 degree of success or a critical success (a natural +4). The character must make an endurance check or pass out. Afterwards the character’s endurance is reduced by 1. It takes 15 minutes of rest to regain each point of fortitude.
In order to cast a spell caster must scribe into a special book incantations and rituals of the spell. The cost of scribing a spell into a spell is 100d per level of spell. In addition to the cost it takes a number of days equal to the spell level to scribe the spell in the spell book.
The caster must set aside one hour of study per spell level per spell per month in order to cast spells from memory.
At character creation the caster buys his initial spells from his character's starting funds.
With the right aspect the caster can use spontaneous magic. Instead of casting spells learned from a spell book, the character performs a series of meditations and rituals to memorize and attune to one of the ten arts of magic. This requires 1,000d worth of components and ten weeks of time.
Afterwards the character can cast any spell from that art with an additional -4 to his Thaumatology roll. The character can only attune to as many arts equal to his Intelligence score in addition to the Art of the Forge.
Starting characters are attuned with one art plus the Forge.
Any spell can be cast as a ten minute ritual. In general mages can cast any spell in their spell book as a ritual without incurring fatigue except on a critical failure (-4).
For mages practicing spontaneous magic they can cast any spell out of a spell book or any spell in the arts they have learned. Any spell cast from their knowledge of the arts is cast at a -4 penalty.
Saving Throws and Spell Effects
The degree of success of the ritual roll is used as the target number for any required saving throws. For example a mage cast a sleep spell and rolls a +4. Since sleep requires a 2 or better to cast the degree of success is 2. The target now needs to make a will save of 2 or higher. The degree of success is also used in some spell to determine how effective the spell is.