What does it mean for school of magic to be prohibited?

[ChudoJogurt]

When creating a wizard character, one can specialise in certains schools, while "giving up" others.
But while the mechanics of it are very simple, I'm not sure what sort of in-game reality is it supposed to reflect.

Is it a deficiency of education?
Is it a deficiency of wizards talent?
Is it something else entirely?

[Kelb_Panthera]

Standard fluff is that he's chosen to so thoroughly neglect the school that he can't work with it at all unless he makes a special effort to do so by either multiclassing into another arcane class that does have access to those spells or by taking a chain of feats from Lost Empires of Faerun that restores a prohibited school.

You can adujst that to a lack of interest or talent in that field if you want. The exact logic behind the mechanics doesn't have to be perfectly static from one instance to the next.

[Odin's Eyepatch]

It can be whatever you want, but my own view is that it's a conscientious decision not to learn the spells from that school.

You cannot cast spells from your prohibited schools, not even via wands or scrolls (unless UMD). Effectively, they are not on your wizard spell list. Furthermore, you take a -5 penalty on any spellcraft check regarding your prohibited schools. Since wizards are usually defined as characters who gain their magic by studying, I feel like the above effects are best explained by the wizard just not spending the time to study those schools of magic.

I feel like it's fair to say that specialising in one school just doesn't allow enough time to study in every other school.

It's a bit like dropping history and arts at school to focus on maths and advanced maths. There's only so many hours in the day.

[schreier]

From a crunch perspective - it seems that it redefines your class list so as to exclude that school.

Extrapolating to fluff - why can a wizard not cast spells from other classes anyways? In Forgotten Realms, you have the weave - and you learn to access the weave in certain ways as part of your power. I would think that, the way you access the weave with a prohibited class does not allow you to access the part of the weave related to that school any more.

[Psyren]

Complete Mage has some detail around the in-universe fluff for spell schools and specialization. The limitation appears to be "time and energy."

SCHOOL SPECIALIZATION

Wizards understand the school approach to arcane magic so well that they can use a single school as the focal point for their magical efforts. Doing this is commonly known as specializing in a school.
...
A few scholars maintain that some schools naturally oppose each other; however, few wizards believe this is truly so. In fact, a school specialist can choose any two prohibited schools. Specialists must choose prohibited schools for the simple reason that opting for a specialty doesn't leave them enough time or energy to learn spells from all the schools. Still, rivalries between students of particular schools have arisen over the years, and certain schools appeal more to some practitioners than to others.

[Jay R]

It is a balancing measure to keep specialist wizards from being totally superior to generalists. The rules do not give a clear in-world reason for it.

So feel free to make up your own reasons for your character, or ask the DM for why it works that way in his universe.

My in-world assumption would be that it takes a certain amount and type of mental ability for your brain can hold onto all eight schools of magic. It takes a greater amount and different type to hold onto one on a specialist level. The brain is simply incapable of doing both, for a reason that is analogous to the fact that a human can't wield more than two swords. We can see the two arms, and we can't see the various brain areas, so it doesn't look similar, but somehow, it really is.

Just don't believe that your reason can be used to change the rule.

"OK, I didn't have enough time and energy to study necromancy and evocation when I was becoming an illusionist. I'm fifth level now and already an illusionist, so I have time and energy now. I'll go back and study those spells now, so I can be an illusionist and use all spells." No. Your in-world justification cannot change the actual rule.

[Odin's Eyepatch]

Looking at other reasons why a school be prohibited: they could be personal reasons too.

A wizard swearing to never learn necromancy because necromancy is evil?
Maybe a wizard deems that enchantments is forcing others to act against their wishes, and therefore never wishes to learn from such a school?

I've even seen a wizard refuse to learn any spell from the teleportation school because he gets "teleportation sickness".

[Falontani]

What about classes that require you to specialise further by dropping more schools of magic later?

And can a specialist wizard use their prohibited schools when casting spells from another class? It doesn't specify wizard spells, but specifies spells, scrolls, and even wands

[Psyren]

What about classes that require you to specialise further by dropping more schools of magic later?

And can a specialist wizard use their prohibited schools when casting spells from another class? It doesn't specify wizard spells, but specifies spells, scrolls, and even wands

The answer to both of these questions is energy, which is mechanically represented by spell slots.

A wizard at a given level has a finite amount of personal energy, determined primarily by their class level and affected by their Intelligence modifier (which provides bonus slots) - either higher Inteliigence translates directly into more of this energy, or it means that that wizard can more efficiently use the finite energy they have, getting more bang for their buck. Either way, this energy gives them a discrete number of slots for any given spell level.

Specialist Wizards are individuals who learn how to focus this energy on specific schools of magic, thus getting additional slots they can use to prepare extra spells aligning with that energy. However, the techniques they use make that energy unsuitable to preparing other schools, which effectively become prohibited for them.

[Clementx]

One thing from fluff is that wizards devise their own spell language/shorthand when creating their spellbook, hence deciphering another's taking a Spellcraft check.

Assume your master never taught you anything about Illusion. You never took a class in it. When writing your foundational system for channeling arcane energy, you never thought to incorporate perception as an aspect of reality.

Take early atomic physics. No one knew about radioactive decay, so there was an entire fundamental force, the weak nuclear, missing. There are particles and quantum fields completely ignored, but they cobbled together something that explained a lot of what they knew so far. Now imagine having to learn an entire new language to doctoral levels to even start talking about it, rather than math being international.

[schreier]

The real fluff challenge, as listed above, is explaining how you forget spells you knew in a banned school

[Kelb_Panthera]

The real fluff challenge, as listed above, is explaining how you forget spells you knew in a banned school

You don't. At least not with any of the classes that leap to mind. They say you can continue to use the spells you've already learned and any items that produce them but you can't learn any more from that school or use items other than those.

[Powerdork]

You don't have a game tagged; I'm going to assume you're talking about 3.5, and note that Pathfinder wizards treat opposition schools differently, using two daily spell charges to prepare the one ready-to-cast spell and taking a skill check penalty to craft magic items using spells from opposition schools.

In my eyes, a wizard's understanding of arcane theory weighs on the mind; triply so if the wizard wants to devote herself to a school so intensely that she can prepare a spell of each level from it on top of normal spell allotments. It's a matter of not having the time to learn the basics and practicalities of another field related to yours because you're devoting so many waking hours to the practice of your passion.