Dual-School Spells for Advanced Learning (Dread Necromancer)

Question

A player in my group plays an evil cleric/dread necromancer. He now gets Advanced Learning. It says in the dread necromancer class description:

The spell must be a cleric or wizard spell of the necromancy school[...]

My PC has chosen a dual-school spell (abjuration/necromancy) and asked me, if that's okay. Honestly, I can't find anything about that in the rules - neither confirming nor denying. The only thing I found is in the PHB 2:

Effects that prevent a spellcaster from accessing one school of a dual-school spell prevent all access to that spell. For example, a specialist wizard cannot learn a dual-school spell if either of the spell’s schools is one of his prohibited schools.

But the dread necromancer doesn't have prohibited schools. So, can he take dual-school spells as long one of the schools is necromancy?

Answer 1

The Dread Necromancer can learn a dual-school spell with Advanced Learning, so long as one of the spell schools is Necromancy.

As well as the text quoted in your question, the PHB II also states, of dual-school spells:

In all cases, treat these spells as if they belonged to both schools simultaneously.

A dual-school Abjuration/Necromancy spell is treated as if it is both an Abjuration spell and a Necromancy spell. Since it's treated as if it were a Necromancy spell, that means it is a valid choice for the Dread Necromancer's Advanced Learning class feature. That it also happens to be treated as an Abjuration spell doesn't matter, because as you've correctly surmised, nothing prevents the Dread Necromancer from learning Abjuration spells (or any other kind of spell).

If the wording of the Advanced Learning feature was like "The spell must not be of any school except Necromancy", then the argument would be that the choice is not valid, because as an Abjuration spell it would happen to be a spell of a school that is not Necromancy. Luckily, the real wording is nothing like that.

Answer 2

Dual-school spells never really caught on; I don’t think any were ever printed outside of Player’s Handbook II. So it’s no surprise that Heroes of Horror doesn’t cover them. There simply aren’t any rules for this situation. The one you quote about prohibited schools is closest, but as you say, that doesn’t really apply.

Ultimately, the restriction on the dread necromancer’s advanced learning is thematic; it’s not about balance. And the dual-school spells really aren’t very good anyway. So really, it’s up to you whether you want to allow it or not, whether the particular spell seems appropriate for a dread necromancer. I would certainly allow it.