If D&D's core magic rules were more Vancian.

[Agrippa]

A spell in essence corresponds to a code, or set of instructions, inserted into the sensorium of an entity which is able and not unwilling to alter the environment in accordance with the message conveyed by the spell. The entities are not necessarily, 'intelligent,' nor even 'sentient,' and their conduct, from the tyro's point of view, is unpredicable, capricious and dangerous.

The most pliable and cooperative of these creatures range from the lowly and frail elementals, through the sandestins. More fractious entities are known .. as 'daihak,' which include 'demons' and 'gods.' A magician's power derives from the abilities of the entities he is able to control. Every magician of consequence employes one or more sandestins.

From this you get the idea that magic is basically the reprograming of pre-existing entities (sort of like free roaming AIs), instead of a direct manipulation of the elements, life, time, gravity or energy. Unless of course you are reprograming the fundemental forces and building blocks of the universe and those are the entities you're reprograming. Oddly enough, as mentioned here, the Tome of Battle's maneuvers readied system would be a closer fit than the classic spells per day formula. Though some spells would have longer preparation times than others. So what do you think this would do for game balance?

[bhu]

It sounds like you have to deal with/control entities to get spells so limit spells by the entities you have sway/influence over.

[linklord231]

Seems like an invitation for a certain type of DM  to play "Mother May I" with wizards.
"The Sandestin don't feel like honoring your spell. Nothing happens.
At least the gods can't take back spells once they've been granted, according to the fluff.

[bhu]

Actually im thinking something like binder might be closer

[wotmaniac]

Actually im thinking something like binder might be closer

and/or sha'ir.

[veekie]

Seems like an invitation for a certain type of DM  to play "Mother May I" with wizards.
"The Sandestin don't feel like honoring your spell. Nothing happens.
At least the gods can't take back spells once they've been granted, according to the fluff.

As I understand it, the creature can't really make any choices as to the effects of the spell, because the spell itself is producing the effect by altering the creature. Still it looks like it'd probably take quite a bit of skill to learn the use and applications of each supernatural 'platform' you'd be coding on. They hardly all work the same way.

[RobbyPants]

There could be some type of d20 check if you want to represent the non-predictable aspect of it. A powerful wizard controls the lesser entities with no trouble, but the more powerful the source, the higher the DC.

Personally, I'm not sure the game needs extra die rolling, but it's probably the easiest way to frame it using existing mechanics. The trick is not allowing the caster to add a billion modifiers to the roll, pushing him off the RNG. It should probably be a flat-out caster level check against a DC based on spell level.

[veekie]

So basically a binding check to cast the spell, and failure gives certain penalties depending on the creature you're editing.

[linklord231]

As I understand it, the creature can't really make any choices as to the effects of the spell, because the spell itself is producing the effect by altering the creature. Still it looks like it'd probably take quite a bit of skill to learn the use and applications of each supernatural 'platform' you'd be coding on. They hardly all work the same way.

That's what I thought at first, too, but there were a couple bits that made me change my mind. 

A spell in essence corresponds to a code, or set of instructions, inserted into the sensorium of an entity which is able and not unwilling to alter the environment in accordance with the message conveyed by the spell. The entities are not necessarily, 'intelligent,' nor even 'sentient,' and their conduct, from the tyro's point of view, is unpredicable, capricious and dangerous.

The most pliable and cooperative of these creatures range from the lowly and frail elementals, through the sandestins. More fractious entities are known .. as 'daihak,' which include 'demons' and 'gods.' A magician's power derives from the abilities of the entities he is able to control. Every magician of consequence employes one or more sandestins.

I haven't actually got around to reading any of Vance's novels, so this is all I know about the system, but that's the conclusion I came to.  I can totally see it the other way, but the cynical part of me doesn't like even the remote possibility of DM fuckery.  In order to avoid that, you'd need some kind of hard and fast mechanic to determine whether or not you can control a given entity, and thus whether or not your spell is cast successfully.
Maybe something like: Spells with a level less than or equal to 1/4 your level (actual level, not CL) can be cast without any kind of check; the spirits just listen to you.  Spells with a level higher than that require some kind of check to cast properly.  Ideally, the DC of the check would scale such that you'd need to roll an 11 in order to succeed on your highest level spells, but not so much that you get off the RNG at high levels.  You couldn't do CL vs a DC X + spell level, because CL scales twice as fast as spell levels and is relatively easy to boost. 

[awaken_D_M_golem]

ninja'd on Binder and Sha'ir.
The Planar Binding / Planar Ally spells are ~similar.

Erudite needs helper Wizards and then has
higher expenses to get those "spells" and then
has the uniques higher choice costs to use them.
Although its a smidge Sorc-y compared to Vance.

[veekie]

I got a different emphasis out of it though

A spell in essence corresponds to a code, or set of instructions, inserted into the sensorium of an entity which is able and not unwilling to alter the environment in accordance with the message conveyed by the spell. The entities are not necessarily, 'intelligent,' nor even 'sentient,' and their conduct, from the tyro's point of view, is unpredicable, capricious and dangerous.

This indicates to me, a couple of things:
-Firstly, your spell is not the effect. Your spell is a particular corruption of the being's sensory data, in an attempt to get it to intervene. The actual effect is twice removed, your intent manifests as an alteration of the entity's sensory information, the entity decides to act upon this false data, and the actual action it chooses to use in reaction to the deception.

-Secondly, some of these entities have no agenda, it can act and react, but has no higher motive than an instinct. Regardless, your procedure remains uninterrupted, except that it'd be easier to predict the reaction of a creature driven wholly by it's native impulses.

[awaken_D_M_golem]

hmm ... like an Air Elemental -ish Thing
is happening by, gets some Magic thrown
at it, so it casts/creates a Wind Wall type
effect, because that's all it can figure out from
the "jibberish" that so-called Caster yelled out.
Then says hey I'm outta here, and goes back
to playing with pretty clouds.
(said Elemental has an Int of 0 or 1, low Wis)

[veekie]

Mostly like that yeah, to generate a wind wall, you create a false scenario where an air elemental would want to create an obstacle comprised of violent winds.

[awaken_D_M_golem]

Dude with decent Knowledge check:
Oh Pazuzu, by the power of the Anti-Pun-pun
create me this particular 6th level spell effect.
(please ... sir)

Pazuzu:  Oh not you again ... (sigh) ... whatever.

DM:  It'll happen but with a 1 round delay.

Dude:  (whine)

DM:  There's no whining in pazuzu-ball.

[veekie]

*Idle considerations which include convincing an air elemental it really needs to fart, right now.*

[awaken_D_M_golem]

  -- Mommy, where do "cantrips" come from ??

[Cheiromancer]

Vance's "Tales of the Dying Earth" are great fun. I encourage anyone who hasn't read them to do so.

The biggest difference between D&D casting (Gygaxian casting) and Vance's wizards is the number of spells per day. Wizards in the Dying Earth can only prepare a few spells, but they can be quite flexible and powerful.

[sirpercival]

RIP Jack