So I’m going to start off by saying that I’ve never quite understood the major complaints of Vancian magic. And maybe it’s just that I’ve never seen them presented clearly, but a quick moment of googling before starting on this post didn’t help clear things up.
Protip: use Divination to help prepare tomorrow’s spells
As near as I can tell, Vancian casting is the sort where a Wizard has to prepare spells ahead of time, and one fired off he needs to take time to rest and ‘recharge his batteries.’ A common complaint seems to be that a Wizard has to predict what sorts of spells they’ll need at the beginning of the day and if they guess wrong, oh well. That could be pretty frustrating, but as far as 3.X/Pathfinder goes (which seem to get the brunt of the complaints) that’s not actually the case. From the SRD (emphasis mine):
When preparing spells for the day, a wizard can leave some of these spell slots open. Later during that day, she can repeat the preparation process as often as she likes, time and circumstances permitting. During these extra sessions of preparation, the wizard can fill these unused spell slots. She cannot, however, abandon a previously prepared spell to replace it with another one or fill a slot that is empty because she has cast a spell in the meantime. That sort of preparation requires a mind fresh from rest. Like the first session of the day, this preparation takes at least 15 minutes, and it takes longer if the wizard prepares more than one-quarter of her spells.
In many places, the text talks about “preparing spells for the day”, the need for 8 hours of rest followed by 1 hour of preparation, and so on, but the above text notes that a Wizard can leave some slots flexible for when they do know what they’re up against. The Wizard still needs time to prepare, which is a key differentiators between them and spontaneous-casting Sorcerers, but it isn’t a “hope you guess right” situation.
Fire and Forget
Another common complaint seems to be that it doesn’t make sense* that a Wizard needs to re-memorize his spells each time he wants to cast them, that the memories of the spell are somehow ‘burned’ out of his mind as he casts. I did see someone note that this is a pretty interesting thing to think about, and kind of creepy, that casting spells can actually rip thoughts out of your head, or that a spell is a kind of entity that moved out of the mage’s mind and in to the world when cast. I agree that those are neat ideas, but I think they’re also unnecessary.
In many places, the rules talk about a Wizard needing to “memorize” spells, but they also use the term “preparation.” In a lot of ways it seems more reasonable that a Wizard essentially half-casts his spells during preparation, leaving the final 3-second trigger to be completed when he actually intends to use the spell. Under that interpretation it’s not that he forgets the spells he uses, but he has to set them up again. And part of the measure of a mage is how many different spells he can “hold” in that half-cast state at a time (and total, in a day, before being sapped of energy).
Spell Slots vs Mana
The last complaint seems to be that spell slots don’t make sense. This comes in two flavors: the one that argues that magic energy should recharge evenly over time, and the one that argues that you should be able to ‘fit’ more lower-level spells in a higher level spell slot. I don’t think there’s anything particularly wrong with either of those systems, it’s just those aren’t the assumptions that D&D Magic makes. it’s a fairly modular system, and you can pretty easily pull out Vancian magic and substitute any other system in it’s place without changing the rest of the game much t all. But I think spell slots are just as reasonable as any other system.
In the D&D mechanics, magic doesn’t recharge evenly over time; accessing those energies is taxing, and a Wizard needs an extended period of light activity or sleep before he can recover, mentally and physically, to work magic again. I’ve seen mana-point systems that work similarly, where mana won’t regenerate during combat, etc, and it’s really just a design choice. You could easily have X spell slots recover over Y hours if you want and essentially have the same thing as mana.
The question of how many spells should ‘fit’ in a spell slot is a matter of what that slot represents. If a spell slot is a quantum of energy, then I would agree that a slot which can power a 3rd Level spell should contain enough energy for several 1st Level spells. Instead, I think spell slots represent the Wizard’s capacity, both in terms of how many half-spells he can hold at a time and how much casting he can perform in a day. Higher level spells are restricted to the slots they ‘fit’ in because they’re harder to handle and maintain so the Wizard can only manage a couple at a time. And regardless of the spells cast, he can only channel so much energy in a day before he’d tapped out, likely drained physically, mentally, and emotionally.
No system is going to satisfy everyone, because we all have slightly different goals and preferences. I’m not saying that no one should dislike Vancian casting, but I am making the case that Vancian Magic is not less valid as a system than any of it’s competitors.
*While I do talk about the need for game systems to be realistic and “make sense” in order to facilitate role playing and decision making, there are limits — we’re talking about a world with dragons and demons walking the earth, and where a pinch of sulfur and a few hand motions makes a fireball; is it that much more difficult to accept that magic burns away memories as it’s cast?