Is there anyway possible a arcane spell-caster could cast a spell that is not on their list? Like say from Spell Research or reading another caster's spellbook, etc.? I've done quite a bit of research on this and I can't find anything definitive. I understand lists are created for a reason, but as a DM I'm having a really hard time drawing a line for my players. Specifically the Magus of the party. I've heard about the use of spellcraft checks or spell failure but I'd like some precedent to give me a better idea of the mechanics. Any advice would be appreciated. Gratias ago.
Specifically the Magus of the party.
Magus have two Arcana to help out with this:
Spell Blending (Ex) allows him to add Wizard spells to his spellbook and spell list.
Broad Study (Ex) allows him to cast spells of another class and still use Spellstrike and Spell Combat. He must have multiclassed in order to do this.
Wizards can use Independent Research to come up with new spells, or duplicate existing ones. It's highly up to DM discretion.