I start by declaring that Arcane Spells are of the Divination, Transmutation, and Universal schools. Any sorcerer or wizard can cast spells out of those schools.
The Conjuration school is also available to both sorcerers and wizards, but is not an Arcane spell for reasons I'll get into later.
Sorcerers can cast Evocation spells (plus Arcane spells and Conjuration spells).
Wizards can cast Abjuration and Enchantment spells (plus Arcane spells and Conjuration spells).
Alternatively, both sorcerers and wizards can opt to be either illusionists or necromancers. If this option is taken, then the base spells lists for each class are not available in lieu of either Illusions or Necromancy. They would still get the Arcane spells, but not Conjuration. The choice of sorcerer or wizard for an illusionist or necromancer would determine the basics of how spells work for that particular class.
So available schools look like this:
Sorcerer: Divination, Universal, Transmutation, Conjuration, Evocation
Wizard: Divination, Universal, Transmutation, Conjuration, Enchantment, Abjuration
Illusionist: Divination, Universal, Transmutation, Illusion
Necromancer: Divination, Universal, Transmutation, Necromancy
This makes sorcerers and wizards quite different. I feel bad that wizards can't cast fireball anymore, but their access to Enchantment and Abjuration spells still makes them quite useful.
I'm not sure that illusionists and necromancers should be able to cast Transmutation spells. And perhaps I should move that school out of my Arcane spell class and into both sorcerer and wizard.
Really, Transmutation is a hard one. There are spells in it I'd like to go to wizards, and other spells I'd like to go to sorcerers.
And now, I'd like to hear what all of you think of this thought experiement?