Allowing spells to have multiple schools, what would be the implication?

[Mastikator]

Let's say that we changed the magic system in a very small way, spells can have two or more schools of magic. Any spell that is ambiguous between two schools just gets both. So for example: summon undead is now both necromancy AND conjuration.

What is the implications? What are the downsides? One I can think of is that some class features lets you pick spells from specific schools, or gain benefits to specific schools and having a larger pool of spells to choose/benefit would boost those (sub)classes.

[Amnestic]

Potentially expands the pool of spells EK fighters and AT rogues can get.

Slight boost to wizards who are: abjuration (more wards), conjuration (concentration), divination (spell restoration), enchantment (split enchantment), evocation (sculpt+empower), and necromancy (grim harvest) depending on how much crossover there is.

Also scribing gets cheaper for all of the spell school wizard subclasses, albeit slightly.

[Valmark]

In addition to what Amnestic said the new sorcerers get more spells to pick from for their subclass bonus spells.

Non-detection would protect from more spells. There might be others like these but I can't think of any.

[Randomthom]

Let's say that we changed the magic system in a very small way, spells can have two or more schools of magic. Any spell that is ambiguous between two schools just gets both. So for example: summon undead is now both necromancy AND conjuration.

What is the implications? What are the downsides? One I can think of is that some class features lets you pick spells from specific schools, or gain benefits to specific schools and having a larger pool of spells to choose/benefit would boost those (sub)classes.

Posivite effect, Divination might actually have some spells in the 6th-8th level bracket! (For Wizards, there is precisely 1 divination spell in that range.)