Can a Specialist Wizard multiclass to cast spells from his prohibited schools?

Question

I've had DMs rule both ways on this..I haven't seen any official RAWs on this so I was hoping someone here could point me in the right direction?

If a Wizard specializes (giving him 1-2 prohibited schools) and later multiclasses can his cross class use the prohibited class?

ie, an "illusionist" gives up Evocation & Conjuration and later crosses into Cleric, would he be prohibited from casting healing (conjuration) spells or would it be ok now that it is divine magic and not arcane?

Or does the arcane vs divine source even matter? So the same Wizard instead crosses into Sorcerer, can he now cast Sorcerer spells from the prohibited schools?

Answer 1

Yes, you can. Specialization is a Wizard class feature that affects Wizard spellcasting only. It has no effect on spells from other classes. Complete Arcane, for example, explicitly suggests multiclassing with Sorcerer to get your missing spells.

Complete Arcane pg. 185

One way around at least part of this restriction is for a specialist wizard to take levels in sorcerer, using her sorcerer spellcasting ability to master the spells and magic items she cannot use as a wizard.

The FAQ (which is not a real rules source but may be good for convincing DMs) explicitly answered this question as well.

Specialization would be much clearer if they simply said that the spells were removed from your wizard spell list, and even effects that add spells to your spell list cannot add spells of your banned schools to your wizard spell list. That's what all the specialization rules sum up to, they just chose a long and complicated way to describe it.

However, note that Wizards, like all spellcasters, multiclass poorly. Being behind on spell levels is a very serious blow to your power. The addition of lower-level spells from another class is not nearly enough to justify this, from a purely-mechanical perspective. There are exceptions, but they involve dual-progression PrCs that can be entered with only one level lost, and that have their own class features (like Anima Mage from Tome of Magic or Ultimate Magus from Complete Mage).